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    Logs and metrics for backend services

    This document shows you how to configure and use Cloud Logging and Cloud Monitoring with classic Application Load Balancers, global external Application Load Balancers, and Cloud CDN.

    Logging

    You can enable, disable, and view logs for an external Application Load Balancer backend service . For external Application Load Balancers with backend buckets , logging is automatically enabled and cannot be disabled.

    You enable or disable logging for each backend service. You can configure whether to log all requests or a randomly sampled fraction.

    You must ensure that you don't have a logs exclusion that applies to external Application Load Balancers. For information about how to verify that Cloud HTTP Load Balancer logs are allowed, see Exclusion filters .

    Logs sampling and collection

    The requests (and corresponding responses) handled by load balancer backend virtual machine (VM) instances are sampled. These sampled requests are then processed to generate logs. You control the fraction of the requests that are emitted as log entries according to the logConfig.sampleRate parameter . When logConfig.sampleRate is 1.0 (100%), this means that logs are generated for all of the requests and written to Cloud Logging.

    Optional fields

    Log records contain required fields and optional fields. The What is logged section lists which fields are optional and which are required. All required fields are always included. You can customize which optional fields you keep.

    • If you select include all optional, all optional fields in the log record format are included in the logs. When new optional fields are added to the record format, the logs automatically include the new fields.

    • If you select exclude all optional, all optional fields are omitted.

    • If you select custom, you can specify the optional fields that you want to include, such as tls.protocol,tls.cipher,orca_load_report.cpu_utilization,orca_load_report.mem_utilization .

    For information about customizing optional fields, see Enable logging on a new backend service .

    Enabling logging on a new backend service

    Console

    1. In the Google Cloud console, go to the Load Balancingpage.

      Go to Load balancing

    2. Click the name of your load balancer.

    3. Click Edit.

    4. Click Backend Configuration.

    5. Select Create a backend service.

    6. Complete the required backend service fields.

    7. In the Loggingsection, select the Enable loggingcheckbox.

    8. Set a Sample ratefraction. You can set a number from 0.0 through 1.0 , where 0.0 means that no requests are logged and 1.0 means that 100% of the requests are logged. The default value is 1.0 .

    9. Optional: To include all the optional fields in the logs, in the Optional fieldssection, click Include all optional fields.

    10. To finish editing the backend service, click Update.

    11. To finish editing the load balancer, click Update.

    gcloud

    Create a backend service and enable logging by using the gcloud compute backend-services create command .

    gcloud compute backend-services create BACKEND_SERVICE 
\
    --global \
    --enable-logging \
    --logging-sample-rate= VALUE 
\
    --load-balancing-scheme=EXTERNAL_MANAGED \
    --logging-optional= LOGGING_OPTIONAL_MODE 
\
    --logging-optional-fields= OPTIONAL_FIELDS

    The gcloud compute backend-services create command supports the following fields:

    • --global indicates that the backend service is global. Use this field for backend services used with global external Application Load Balancers.
    • --enable-logging enables logging for that backend service.
    • --logging-sample-rate lets you specify a value from 0.0 through 1.0 , where 0.0 means that no requests are logged and 1.0 means that 100% of the requests are logged. This field is only meaningful with the --enable-logging parameter. Enabling logging but setting the sampling rate to 0.0 is equivalent to disabling logging. The default value is 1.0 .

    • --logging-optional lets you specify the optional fields that you want to include in the logs. These fields are supported only with global external Application Load Balancers.

      • INCLUDE_ALL_OPTIONAL to include all optional fields.

      • EXCLUDE_ALL_OPTIONAL (default) to exclude all optional fields.

      • CUSTOM to include a custom list of optional fields that you specify in OPTIONAL_FIELDS .

    • --logging-optional-fields lets you specify a comma-separated list of optional fields that you want to include in the logs.

      For example, tls.protocol,tls.cipher can only be set if LOGGING_OPTIONAL_MODE is set to CUSTOM . If you use custom metrics and want to log elements of the ORCA load report, you set LOGGING_OPTIONAL_MODE to CUSTOM and specify which elements must be logged in the OPTIONAL_FIELDS field. For example, orca_load_report.cpu_utilization,orca_load_report.mem_utilization .

    Enabling logging on an existing backend service

    Console

    1. In the Google Cloud console, go to the Load Balancingpage.

      Go to Load balancing

    2. Click the name of your load balancer.

    3. Click Edit.

    4. Click Backend Configuration.

    5. Click Editnext to your backend service.

    6. In the Loggingsection, select the Enable loggingcheckbox.

    7. In the Sample ratefield, set the sampling probability. You can set a number from 0.0 through 1.0 , where 0.0 means that no requests are logged and 1.0 means that 100% of the requests are logged. The default value is 1.0 .

    8. Optional: To include all the optional fields in the logs, in the Optional fieldssection, click Include all optional fields.

    9. To finish editing the backend service, click Update.

    10. To finish editing the load balancer, click Update.

    gcloud

    Enable logging on an existing backend service with the gcloud compute backend-services update command .

    gcloud compute backend-services update BACKEND_SERVICE 
\
    --global \
    --enable-logging \
    --logging-sample-rate= VALUE 
\
    --logging-optional= LOGGING_OPTIONAL_MODE 
\
    --logging-optional-fields= OPTIONAL_FIELDS

    where

    • --global indicates that the backend service is global. Use this field for backend services used with global external Application Load Balancers.
    • --enable-logging enables logging for that backend service.
    • --logging-sample-rate lets you specify a value from 0.0 through 1.0 , where 0.0 means that no requests are logged and 1.0 means that 100% of the requests are logged. Only meaningful with the --enable-logging parameter. Enabling logging but setting the sampling rate to 0.0 is equivalent to disabling logging. The default value is 1.0 .

    • --logging-optional lets you specify the optional fields that you want to include in the logs. These fields are supported only with global external Application Load Balancers.

      • INCLUDE_ALL_OPTIONAL to include all optional fields.

      • EXCLUDE_ALL_OPTIONAL (default) to exclude all optional fields.

      • CUSTOM to include a custom list of optional fields that you specify in OPTIONAL_FIELDS .

    • --logging-optional-fields lets you specify a comma-separated list of optional fields that you want to include in the logs.

      For example, tls.protocol,tls.cipher . Can only be set if LOGGING_OPTIONAL_MODE is set to CUSTOM . If you use custom metrics and want to log elements of the ORCA load report, you set LOGGING_OPTIONAL_MODE to CUSTOM and specify which elements must be logged in the OPTIONAL_FIELDS field. For example, orca_load_report.cpu_utilization,orca_load_report.mem_utilization .

    Disabling or modifying logging on an existing backend service

    Console

    1. In the Google Cloud console, go to the Load Balancingpage.

      Go to Load balancing

    2. Click the name of your load balancer.

    3. Click Edit.

    4. Click Backend Configuration.

    5. Click Editnext to your backend service.

    6. To disable logging entirely, in the Loggingsection, clear the Enable loggingcheckbox.

    7. If you leave logging enabled, you can set a different Sample ratefraction. You can set a number from 0.0 through 1.0 , where 0.0 means that no requests are logged and 1.0 means that 100% of the requests are logged. The default value is 1.0 . For example, 0.2 means 20% of the sampled requests generate logs.

    8. To finish editing the backend service, click Update.

    9. To finish editing the load balancer, click Update.

    gcloud: Global mode

    Disable logging on a backend service with the gcloud compute backend-services update command .

    Disabling logging entirely

    gcloud compute backend-services update BACKEND_SERVICE 
\
    --global \
    --no-enable-logging

    where

    • --global indicates that the backend service is global. Use this field for backend services used with global external Application Load Balancers.
    • --no-enable-logging disables logging for that backend service.

    Enabling logging optional fields on an existing backend service

    gcloud compute backend-services update BACKEND_SERVICE 
\
    --global \
    --enable-logging \
    --logging-sample-rate= VALUE 
\
    --logging-optional= LOGGING_OPTIONAL_MODE 
\
    --logging-optional-fields= OPTIONAL_FIELDS

    where

    • --logging-sample-rate lets you specify a value from 0.0 through 1.0 , where 0.0 means that no requests are logged and 1.0 means that 100% of the requests are logged. Only meaningful with the --enable-logging parameter. Enabling logging but setting the sampling rate to 0.0 is equivalent to disabling logging. The default value is 1.0 .

    • --logging-optional lets you specify the optional fields that you want to include in the logs:

      • INCLUDE_ALL_OPTIONAL to include all optional fields.

      • EXCLUDE_ALL_OPTIONAL (default) to exclude all optional fields.

      • CUSTOM to include a custom list of optional fields that you specify in OPTIONAL_FIELDS .

    • --logging-optional-fields lets you specify a comma-separated list of optional fields that you want to include in the logs.

      For example, tls.protocol,tls.cipher can only be set if LOGGING_OPTIONAL_MODE is set to CUSTOM . If you use custom metrics and want to log elements of the ORCA load report, you set LOGGING_OPTIONAL_MODE to CUSTOM and specify which elements must be logged in the OPTIONAL_FIELDS field. For example, orca_load_report.cpu_utilization,orca_load_report.mem_utilization .

    Updating logging optional mode from CUSTOM to others

    gcloud compute backend-services update BACKEND_SERVICE 
\
    --global \
    --enable-logging \
    --logging-sample-rate= VALUE 
\
    --logging-optional= LOGGING_OPTIONAL_MODE 
\
    --logging-optional-fields=

    where

    • --logging-optional lets you specify the optional fields that you want to include in the logs:

      • INCLUDE_ALL_OPTIONAL to include all optional fields.

      • EXCLUDE_ALL_OPTIONAL (default) to exclude all optional fields.

    • --logging-optional-fields must be explicitly configured as shown to clear any existing CUSTOM fields. The API doesn't let you combine a non- CUSTOM mode with CUSTOM fields.

    Modifying the logging sample rate

    gcloud compute backend-services update BACKEND_SERVICE 
\
    --global \
    --logging-sample-rate= VALUE

    gcloud: Classic mode

    Disable logging on a backend service with the gcloud compute backend-services update command .

    Disabling logging entirely

    gcloud compute backend-services update BACKEND_SERVICE 
\
    --global \
    --no-enable-logging

    where

    • --global indicates that the backend service is global. Use this field for backend services used with a classic Application Load Balancer.
    • --no-enable-logging disables logging for that backend service.

    Modifying the logging sample rate

    gcloud compute backend-services update BACKEND_SERVICE 
\
    --global \
    --logging-sample-rate= VALUE

    where

    • --global indicates that the backend service is global. Use this field for backend services used with a classic Application Load Balancer.
    • --logging-sample-rate lets you specify a value from 0.0 through 1.0 , where 0.0 means that no requests are logged and 1.0 means that 100% of the requests are logged. Only meaningful with the --enable-logging parameter. Enabling logging but setting the sampling rate to 0.0 is equivalent to disabling logging.

    View logs

    To follow step-by-step guidance for this task directly in the Google Cloud console, click Guide me :

    Guide me

    HTTP(S) logs are indexed first by a forwarding rule , then by a URL map .

    To view logs, go to the Logs Explorerpage:

    Go to Logs Explorer

    • To view all logs, in the Resourcefilter menu, select Cloud HTTP Load Balancer  > All forwarding rules.

    • To view logs for one forwarding rule, select a single forwarding rule name.

    • To view logs for one URL map, select a forwarding rule, and then select a URL map.

    Log fields of type boolean typically only appear if they have a value of true . If a boolean field has a value of false , that field is omitted from the log.

    UTF-8 encoding is enforced for log fields. Characters that are not UTF-8 characters are replaced with question marks. For classic Application Load Balancers and global external Application Load Balancers , you can export logs-based metrics using resource logs ( resource.type="http_load_balancer" ). The metrics created are based on the Application Load Balancer Rule (Logs-based Metrics)resource ( l7_lb_rule ), which is available under Cloud Monitoring dashboards instead of under the https_lb_rule resource.

    What is logged

    External Application Load Balancer log entries contain information useful for monitoring and debugging your HTTP(S) traffic. Log records contain required fields, which are the default fields of every log record.

    Log records contain optional fields that add additional information about your HTTP(S) traffic. Optional fields can be omitted to save storage costs.

    Some log fields are in a multi-field format, with more than one piece of data in a given field. For example, the tls field is of the TlsInfo format, which contains the earlyDataRequest field. These multi-field fields are described in the following record format table.
    Field
    Field format
    Field type: Required or Optional
    Description
    severity
    insertID
    logName
    LogEntry
    Required
    The general fields as described in a log entry.
    timestamp
    string ( Timestamp format)
    Optional
    The time when the first layer GFE receives the request.
    httpRequest
    HttpRequest
    Required
    A common protocol for logging HTTP requests.

    HttpRequest.protocol isn't populated for resource.type="http_load_balancer"

    .
    resource
    MonitoredResource
    Required

    The MonitoredResource is the resource type associated with a log entry.

    The MonitoredResourceDescriptor describes the schema of a MonitoredResource object by using a type name and a set of labels. For more information, see Resource labels .

    jsonPayload
    object ( Struct format)
    Required
    The log entry payload that is expressed as a JSON object. The JSON object contains the following fields:
    • statusDetails
    • backendTargetProjectNumber
    • overrideResponseCode
    • errorService
    • errorBackendStatusDetails
    • authzPolicyInfo
    • loadBalancingScheme
    • tls
    • orca_load_report
    string
    Required
    The statusDetails field holds a string that explains why the load balancer returned the HTTP status code that it did. For more information about these log strings, see statusDetails HTTP success messages and statusDetails HTTP failure messages .
    string
    Required
    The backendTargetProjectNumber field holds the project number where the backend target—backend service or backend bucket—has been created. This field is in the format: "projects/ PROJECT_NUMBER " . This information is only available for global external Application Load Balancers using custom error responses .
    integer
    Required
    The overrideResponseCode holds the override response code applied to the response sent to the client. This information is only available for global external Application Load Balancers using custom error responses .
    string
    Required
    The errorService field holds the backend service that provided the custom error response. This information is only available for global external Application Load Balancers using custom error responses .
    string
    Required
    The errorBackendStatusDetails field holds the statusDetails of the final response served to the client. This information is only available for global external Application Load Balancers using custom error responses .
    AuthzPolicyInfo
    Required
    The authzPolicyInfo field stores information about the authorization policy result. This information is only available for global external Application Load Balancers that have enabled authorization policies . For more information, see what is logged for authorization policies .
    string
    Optional
    The loadBalancingScheme field is only populated if you use the classic Application Load Balancer migration feature. This field holds a string that describes which load balancing scheme was used to route the request. The possible values are either EXTERNAL or EXTERNAL_MANAGED .
    TlsInfo
    Required

    The tls field holds the TlsInfo field that specifies the TLS metadata for the connection between the client and the load balancer. This field is only available if the client is using TLS/SSL encryption.

    Use the --logging-optional-fields parameter to specify which elements must be logged:

    • Optional: tls.protocol
    • Optional: tls.cipher
    • Required: tls.earlyDataRequest

    You can't set --logging-optional-fields to tls to specify all elements.

    OrcaLoadReport
    Optional

    The orca_load_report field contains some or all elements of the ORCA load report returned by the backend. This field is only present if the backend returns an ORCA load report and you configured the load balancer to log the ORCA load report.

    Use the --logging-optional-fields parameter to specify which of the following elements of the ORCA load report must be logged:

    • orca_load_report.cpu_utilization
    • orca_load_report.mem_utilization
    • orca_load_report.request_cost
    • orca_load_report.utilization
    • orca_load_report.rps_fractional
    • orca_load_report.eps
    • orca_load_report.named_metrics
    • orca_load_report.application_utilization

    You can also set --logging-optional-fields to orca_load_report to specify that all elements must be logged.

    TlsInfo field format

    Field Field format Field type: Required or Optional Description
    protocol
    		string Optional TLS protocol that clients use to establish a connection with the load balancer. Possible values are TLSv1 , TLSv1.1 , TLSv1.2 , TLSv1.3 , or QUIC . This value is set to NULL if the client is not using TLS/SSL encryption.
    cipher
    		string Optional TLS cipher that clients use to establish a connection with the load balancer. This value is set to NULL if the client isn't using HTTP(S) or the client isn't using TLS/SSL encryption.
    earlyDataRequest
    		 boolean Required The request includes early data in the TLS handshake.

    Resource labels

    The following table lists the resource labels for resource.type="http_load_balancer" .

    Field Type Description
    backend_service_name
    		string The name of the backend service.
    forwarding_rule_name
    		string The name of the forwarding rule object.
    project_id
    		string The identifier of the Google Cloud project associated with this resource.
    target_proxy_name
    		string The name of the target proxy object referenced by the forwarding rule.
    url_map_name
    		string The name of the URL map object configured to select a backend service.
    zone
    		string The zone in which the load balancer is running. The zone is global .

    statusDetails HTTP success messages

    statusDetails (successful) Meaning Common accompanying response codes
    byte_range_caching
    		The HTTP request was served using Cloud CDN byte range caching . Any cacheable response code is possible.
    response_from_cache
    		The HTTP request was served from a Cloud CDN cache. Any cacheable response code is possible.
    response_from_cache_validated
    		The return code was set from a Cloud CDN cached entry that was validated by a backend. Any cacheable response code is possible.
    response_sent_by_backend
    		The HTTP request was proxied successfully to the backend, and the response was returned by the backend. The HTTP response code is set by the software running on the backend.

    statusDetails HTTP failure messages

    statusDetails (failure)
    Meaning
    Common accompanying status codes
    aborted_request_due_to_backend_early_response
    A request with body was aborted due to the backend sending an early response with a status code. The response was forwarded to the client. The request was terminated.
    4XX or 5XX
    backend_connection_closed_after_partial_response_sent
    The backend connection closed unexpectedly after a partial response had been sent to the client.

    The HTTP status code is set by the software running on the backend. HTTP status code 0 (zero) means that the backend sent incomplete HTTP headers.

    The HTTP status code is 101 if the HTTP(S) connection was upgraded to a websocket connection.

    backend_connection_closed_before_data_sent_to_client
    The backend unexpectedly closed its connection to the load balancer before the response was proxied to the client.

    502, 503

    The HTTP status code is 101 if the HTTP(S) connection was upgraded to a websocket connection.

    backend_early_response_with_non_error_status
    The backend sent a non-error status code ( 1 XX or 2 XX ) to a request before receiving the whole request body.
    502 , 503
    backend_interim_response_not_supported
    The backend sent an interim 1 XX status code to the request in a context where interim responses aren't supported.

    502 , 503

    backend_response_corrupted
    The HTTP response body sent by the backend has invalid chunked transfer-encoding or is otherwise corrupted.
    Any status code possible depending on the nature of the corruption. Often 502 , 503 .
    backend_response_headers_too_long
    The HTTP response headers sent by the backend exceeded the allowed limit. See the Header size for external Application Load Balancers section for more information.
    502 , 503
    backend_timeout

    The backend timed out while generating a response.

    For a websocket connection:

    • For global external Application Load Balancer, a status code is generated when the GFE closes the websocket connection in idle state after the backend service timeout expires.
    • For classic Application Load Balancer, a status code is generated when the GFE closes the websocket connection in either idle or active state, after the backend service timeout expires.

    502 , 503

    The HTTP status code is 101 if the HTTP(S) connection was upgraded to a websocket connection.

    banned_by_security_policy
    The request was banned by a Cloud Armor rate-based ban rule.
    429
    body_not_allowed
    The client sent an HTTP request with a body, but the HTTP method used doesn't allow a body.
    400
    byte_range_caching_aborted
    The load balancer previously received a response indicating that the resource was cacheable and supported byte ranges. Cloud CDN received an inconsistent response (for example, one with a status code other than the expected 206 Partial Content ). This happened when attempting to perform cache fill using a byte range request . As a result, the load balancer aborted the response to the client.
    2 XX
    byte_range_caching_forwarded_backend_response
    The load balancer previously received a response indicating that the resource was cacheable and supported byte ranges. Cloud CDN received an inconsistent response (for example, one with a status code other than the expected 206 Partial Content ). This happened when attempting to perform cache fill using a byte range request . The load balancer then forwarded the inconsistent response to the client.

    Returned from the backend—any status code is possible.

    byte_range_caching_retrieval_abandoned
    The client canceled a byte range request or validation request initiated by Cloud CDN.

    Returned from the backend—any status code is possible.

    byte_range_caching_retrieval_from_backend_failed_after_partial_response
    A byte range request or validation request initiated by Cloud CDN encountered an error. Refer to the corresponding Cloud Logging log entry for the request initiated by Cloud CDN for the detailed backend status.
    2 XX
    cache_lookup_failed_after_partial_response
    The load balancer failed to serve a full response from Cloud CDN cache due to an internal error.
    2 XX
    cache_lookup_timeout_after_partial_response
    The Cloud CDN cache lookup stream timed out because the client didn't retrieve the content in a timely manner.
    2 XX
    client_disconnected_after_partial_response
    The connection to the client was broken after the load balancer sent a partial response.

    Returned from the backend—any status code is possible.

    The HTTP status code is 101 if the HTTP(S) connection was upgraded to a websocket connection.

    client_disconnected_before_any_response
    The connection to the client was broken before the load balancer sent any response.

    0

    The HTTP status code is 101 if the HTTP(S) connection was upgraded to a websocket connection.

    client_timed_out
    The Google Front End (GFE) idled out the client connection due to lack of progress while it was proxying either the request or the response.
    0 or 408
    client_cert_invalid_rsa_key_size
    A client leaf or intermediate certificate had an invalid RSA key size. For more information, see Logged errors for closed connections .
    0
    client_cert_unsupported_elliptic_curve_key
    A client or intermediate certificate is using an unsupported elliptic curve. For more information, see Logged errors for closed connections .
    0
    client_cert_unsupported_key_algorithm
    A client or intermediate certificate is using a non-RSA or non-ECDSA algorithm. For more information, see Logged errors for closed connections .
    0
    client_cert_pki_too_large
    The PKI to be used for validation has more than ten intermediate certificates that share the same Subject and Subject Public Key Info. For more information, see Logged errors for closed connections .
    0
    client_cert_chain_max_name_constraints_exceeded
    An intermediate certificate provided for validation had more than ten name constraints. For more information, see Logged errors for closed connections .
    0
    client_cert_chain_invalid_eku
    Either the client certificate or its issuer doesn't have Extended Key Usage (EKU) that includes clientAuth . For more information, see Logged errors for closed connections .
    0
    client_cert_validation_timed_out
    Time limit exceeded while validating the certificate chain. For more information, see Logged errors for closed connections .
    0
    client_cert_validation_search_limit_exceeded
    The depth or iteration limit is reached while attempting to validate the certificate chain. For more information, see Logged errors for closed connections .
    0
    client_cert_validation_not_performed
    You have configured mTLS without setting up a TrustConfig . For more information, see Logged errors for closed connections .
    0
    client_cert_not_provided
    The client didn't provide the requested certificate during the handshake. For more information, see Logged errors for closed connections .
    0
    client_cert_validation_failed
    Client certificate fails validation with the TrustConfig when hashing algorithms such as MD4, MD5, and SHA-1 are used. For more information, see Logged errors for closed connections .
    0
    config_not_found

    The load balancer is missing project configuration. This can occur intermittently after you've made configuration changes that add a new resource.

    Another cause of the error is that the first-layer GFE fails to communicate with the second-layer GFE. This can be due to an internal error, such as an in-progress rollout, load balancer overload, or intermittent configuration issues.

    These errors are transient in nature and are expected to fall well within the SLA . However, if the error rate exceeds 0.01%, please contact Google Cloud support for further assistance.

    404 , 502 , 503
    direct_response
    The load balancer overrode this request and returned a fixed response.
    You might see any HTTP status code depending on the nature of the issue. For example, the HTTP 410 status code means that the backend is unavailable due to payment delinquency.
    denied_by_security_policy
    The load balancer denied this request because of a Google Cloud Armor security policy .
    Configured in the security policy.
    error_uncompressing_gzipped_body
    There was an error uncompressing a gzipped HTTP response.
    502 , 503
    failed_to_connect_to_backend
    The load balancer failed to connect to the backend. This includes timeouts during the connection phase.
    502 , 503
    failed_to_pick_backend
    The load balancer failed to pick a healthy backend to handle the request.
    502 , 503
    failed_to_negotiate_alpn
    The load balancer and the backend failed to negotiate an application layer protocol (such as HTTP/2) to use to communicate with each other over TLS.
    502 , 503
    headers_too_long
    The request headers were larger than the maximum allowed.
    413
    http_version_not_supported
    HTTP version not supported. Only HTTP 0.9, 1.0, 1.1, and 2.0 are supported.
    400
    internal_error
    Internal error at the load balancer. Normally represents a transient error in the load balancer infrastructure. Retry your query.
    4 XX or 5 XX
    invalid_chunk_framing
    Requests and responses sent with the Transfer-Encoding: Chunked header are not RFC 9112 compliant. As per the RFC, both the chunked_body and the last-chunk fields must end in CRLF .
    400
    invalid_external_origin_endpoint
    The configuration for the external backend is invalid. Review the internet NEG configuration and ensure that it specifies a valid FQDN/IP address and port.
    4 XX
    invalid_request_headers

    The HTTP request headers received from a client contain at least one character that isn't allowed under an applicable HTTP specification.

    For example, header field names that include a double quotation mark ( " ) or any characters outside of the standard ASCII range (that is, any byte >= 0x80 ) are invalid.

    For more information, see:

    400
    invalid_http2_client_header_format
    The HTTP/2 headers from a client are invalid. For more information, see invalid_request_headers .
    400
    invalid_http2_client_request_path

    The HTTP/2 request path from a client contains at least one character that isn't allowed under the URI specification.

    For more information, see the "3.3. Path" section of RFC 3986 .

    400
    multiple_iap_policies
    Multiple Identity-Aware Proxy (IAP) policies cannot be combined. If you have an IAP policy attached to a backend service and another policy attached to a serverless object, remove one of the policies and try again. Serverless objects include App Engine, Cloud Run, and Cloud Run functions.
    500
    malformed_chunked_body
    The request body was improperly chunk encoded.
    411
    request_loop_detected
    The load balancer detected a request loop. This loop might be caused by a misconfiguration where the backend forwarded the request back to the load balancer.
    502 , 503
    required_body_but_no_content_length
    The HTTP request requires a body but the request headers don't include a content length or transfer-encoding chunked header.
    400 , 403 , 411
    retriable_error

    The load balancer has encountered an infrastructure error and the request can be retried. This can occur intermittently after you've made configuration changes that add or reference a new resource.

    This can also occur when the first-layer GFE fails to communicate with the second-layer GFE due to an internal error, such as an in-progress rollout, load balancer overload, or intermittent configuration issue.

    These errors are transient in nature and are expected to fall well within the SLA . However, if the error rate exceeds 0.01% over a sustained period, please contact Google Cloud support for further assistance.

    404 , 502 , 503
    secure_url_rejected
    A request with an https:// URL was received over a plaintext HTTP/1.1 connection.
    400
    server_cert_chain_exceeded_limit
    The server certificate chain is too long (more than 10 intermediate certificates included with the server certificate).
    502 , 503

    server_cert_chain_invalid_eku

    The server certificate has an Extended Key Usage (EKU) extension field but that field doesn't include serverAuth .

    server_cert_chain_max_name_constraints_exceeded

    An intermediate certificate provided for validation had more than 10 name constraints.
    502 , 503
    server_cert_exceeded_size_limit
    The server certificate payload (including any intermediate certificates) is too large (more than 16 KB).
    503
    server_cert_invalid_rsa_key_size

    A server or an intermediate certificate has an invalid RSA key size.

    No validation is performed.

    RSA keys can range from 2048 to 4096 bits.

    503
    server_cert_not_provided
    The server did not provide the requested certificate during the handshake.
    503
    server_cert_pki_too_large

    The PKI to be used for validation has more than ten intermediate certificates that share the same Subject and Subject Public Key Info.

    No validation is performed.

    503
    server_cert_trust_config_not_found
    Matching TrustConfig not found.
    503
    server_cert_unsupported_elliptic_curve_key

    A server or an intermediate certificate is using an unsupported elliptic curve.

    No validation is performed.

    Valid curves are P-256 and P-384.

    503
    server_cert_unsupported_key_algorithm

    A server or an intermediate certificate is using a non-RSA or non-ECDSA algorithm.

    No validation is performed.

    503
    server_cert_validation_internal_error
    Internal error validating certificate chain.
    503
    server_cert_validation_not_performed

    You configured mTLS without setting up a TrustConfig resource.

    503
    server_cert_validation_search_limit_exceeded

    The depth or iteration limit is reached while attempting to validate the certificate chain.

    The maximum depth for a certificate chain is ten, including the root and server certificates. The maximum number of iterations is 100 (certificates examined to validate the server certificate chain).

    503
    server_cert_validation_timed_out
    The time limit is exceeded while attempting to validate the certificate chain.
    503
    server_cert_validation_unavailable
    Service is unable to perform certificate chain validation.
    503
    ssl_certificate_san_verification_failed
    The load balancer cannot find a Subject Alternative Name (SAN) in the SSL certificate presented by the backend that matches the configured hostname.
    502 , 503
    ssl_certificate_chain_verification_failed
    The SSL certificate presented by the backend failed SSL certificate verification.
    502 , 503
    throttled_by_security_policy
    The request was blocked by a Cloud Armor throttle rule.
    429
    unsupported_method
    The client supplied an unsupported HTTP request method.
    400
    unsupported_100_continue
    The client request included the 'Expect: 100-continue' header on a protocol that doesn't support it.
    400
    upgrade_header_rejected
    The client HTTP request contained the Upgrade header and was refused.
    400
    websocket_closed
    The websocket connection was closed.
    101
    websocket_handshake_failed
    The websocket handshake failed.
    Any status code possible depending on the nature of the handshake failure.
    request_body_too_large
    The HTTP request body exceeded the maximum supported by the backend. Not applicable for VM backends.
    413
    handled_by_identity_aware_proxy
    This response was generated by Identity-Aware Proxy during identity verification of the client before allowing access.

    200 , 302 , 400 , 401 , 403 , 500 , 502 , 503

    429 (throttled by IAP)

    serverless_neg_routing_failed
    The serverless NEG request cannot be dispatched. This error can happen when the region specified in the NEG cannot be reached, or when the resource name (for example, the Cloud Run functions name) cannot be found.
    404 , 502 , 503
    fault_filter_abort
    This error can happen if the customer has configured a fault filter and the fault filter was triggered for the given request.
    The value must be from 200 to 599 .
    early_data_rejected

    The request sent in TLS early data was invalid.

    This might occur in the following cases but isn't limited to them:

    • The TargetHttpsProxy has TLS early data set to STRICT , but the request included query parameters.
    • The TargetHttpsProxy has TLS early data set to STRICT or PERMISSIVE , but the request used a nonidempotent HTTP method (such as POST or PUT).
    425
    service_extension_error

    There was an error calling out to a service extension used by the load balancer.

    This might occur if the Wasm plugin is slow to respond and exceeds the 1 millisecond limit to send its response.

    425

    View logs for mTLS client certificate validation

    To view the logged errors for closed connections during mutual TLS client certificate validation, complete the following steps.

    Console query

    1. In the Google Cloud console, go to the Logs Explorer page.

      Go to Logs Explorer

    2. Click the Show querytoggle.

    3. Paste the following into the query field. Replace FORWARDING_RULE_NAME with the name of your forwarding rule.

      jsonPayload.statusDetails=~"client_cert"
jsonPayload.@type="type.googleapis.com/google.cloud.loadbalancing.type.LoadBalancerLogEntry"
resource.labels.forwarding_rule_name= FORWARDING_RULE_NAME

    4. Click Run query.

    Authorization policy request logs

    The authz_info object in the Load Balancer Log Entry JSON payload contains information about authorization policies. You can configure log-based metrics for traffic allowed or denied by these policies. Check more authorization policies log details .

    Field
    Type
    Description
    authz_info.policies[]
    object
    The list of policies that match the request.
    authz_info.policies[].name
    string
    The name of the authorization policy that matches the request.

    The name is empty for the following reasons:

    • No ALLOW policy matches the request and the request is denied.
    • No DENY policy matches the request and the request is allowed.
    authz_info.policies[].result
    enum
    The result can be ALLOWED or DENIED .
    authz_info.policies[].details
    string
    The details include the following:
    • allowed_as_no_deny_policies_matched_request
    • denied_as_no_allow_policies_matched_request
    • denied_by_authz_extension
    • denied_by_cloud_iap
    authz_info.overall_result
    enum
    The result can be ALLOWED or DENIED .

    Logging for Cloud Armor

    The table for statusDetail HTTP failure messages contains some messages that apply to Cloud Armor. For more information about what Cloud Armor logs, see Use request logging .

    Logging for Shared VPC deployments

    Application Load Balancer logs and metrics are typically exported to the project that has the forwarding rule. Therefore, service admins—owners or users of projects where the backend service is created—won't have access to the load balancer's logs and metrics by default. You can use IAM roles to grant these permissions to service admins. To learn more about the IAM roles that are available, and the steps to provide access, see Grant access to Monitoring .

    Interacting with the logs

    You can interact with the external Application Load Balancer logs by using the Cloud Logging API. The Logging API provides ways to interactively filter logs that have specific fields set. It exports matching logs to Cloud Logging, Cloud Storage, BigQuery, or Pub/Sub. For more information about the Logging API, see Logging API overview .

    Monitoring

    The load balancer exports monitoring data to Monitoring .

    You can use monitoring metrics to do the following:

    • Evaluate a load balancer's configuration, usage, and performance
    • Troubleshoot problems
    • Improve resource utilization and user experience

    Metric reporting frequency and retention

    Metrics for the external Application Load Balancers are exported to Cloud Monitoring in 1-minute granularity batches. Monitoring data is retained for six (6) weeks.

    The dashboard provides data analysis in default intervals of 1H (one hour), 6H (six hours), 1D (one day), 1W (one week), and 6W (six weeks). You can manually request analysis in any interval from 6W to 1 minute.

    Monitoring metrics

    You can monitor the following metrics for external Application Load Balancers.

    The following metrics for global external Application Load Balancers are reported into Cloud Monitoring . These metrics are prepended with loadbalancing.googleapis.com/ .

    Metric
    Name
    Description
    Request count
    https/request_count
    The number of requests served by the external Application Load Balancer
    Request bytes count
    https/request_bytes_count
    The number of bytes sent as requests from clients to the external Application Load Balancer
    Response bytes count
    https/response_bytes_count
    The number of bytes sent as responses from the external Application Load Balancer to clients
    Total latencies
    https/total_latencies

    A distribution of the total latency. Total latency is the time in milliseconds between the first byte of the request received by the proxy and the last byte of the response sent by the proxy. It includes: the time taken by the proxy to process the request, the time taken for the request to be sent from the proxy to the backend, the time taken by the backend to process the request, the time taken for the response to be sent back to the proxy, and the time taken for the proxy to process the response and send the response to the client.

    It doesn't include the RTT between the client and the proxy. Additionally, pauses between requests on the same connection that use Connection: keep-alive do not affect the measurement. This measurement is typically reduced to the 95th percentile in Cloud Monitoring views.

    For websocket connections, this field refers to the entire time duration of the connection. *

    Example: A load balancer has 1 request per second from the UK, all with 100 ms latency, and 9 requests per second from the US, all with 50 ms latency. Over a certain minute there were 60 requests from the UK and 540 requests from the US. Monitoring metrics preserves the distribution over all dimensions. You can request information such as the following:

    • median overall latency (300/600) - 50 ms
    • median UK latency (30/60) - 100 ms
    • 95th percentile overall latency (570/600) - 100 ms
    Frontend RTT †
    https/frontend_tcp_rtt

    A distribution of the frontend RTT. Frontend RTT is the time in milliseconds it takes for data to travel from the client to the proxy and back again. It includes the time taken for a request to travel from the client to the proxy and back from the proxy to the client. This is not updated during the lifetime of the connection. For example, setting up a (TCP) connection with a 3-way handshake would take 1.5 RTTs.

    When requests are processed, the load balancer samples and averages the time it takes for data to travel back and forth between the client and the proxy, and then logs a smoothed RTT value. Smoothed RTT is an algorithm that deals with variations and anomalies that might occur in RTT measurements.

    Backend latencies †
    https/backend_latencies

    A distribution of the backend latency. Backend latency is the time in milliseconds between the first byte of the request received by the backend and the last byte of the response received by the proxy. It includes: the time taken for the request to be sent from the proxy to the backend, the time taken by the backend to process the request, and the time taken for the response to be sent back to the proxy.

    Response code class fraction
    Fraction of total external Application Load Balancer responses that are in each response code class ( 2 xx , 4 xx , ...). In Monitoring, this value is only available on default dashboards. It isn't available for custom dashboards. You can use the Monitoring API to set alerts for it.
    Backend request count
    https/backend_request_count
    The number of requests sent from the external Application Load Balancer to the backends.
    Backend request bytes count
    https/backend_request_bytes_count
    The number of bytes sent as requests from the external Application Load Balancer to the backends.
    Backend response bytes count
    https/backend_response_bytes_count
    The number of bytes sent as responses from the backends (including cache) to the external Application Load Balancer.

    * For monitoring websocket connections, create a backend service specifically for websockets.

    † The sum of Frontend RTT and Backend latencies might not be less than or equal to Total latencies. This is because although we poll RTT over the socket from the GFE to the client at the time the HTTP response is acknowledged, we rely on kernel reporting for some of these measurements, and we cannot be sure that the kernel will have an RTT measurement for the given HTTP response. The end result is a smoothed RTT value that is also affected by previous HTTP responses, SYN/ACKs, and SSL handshakes that aren't affecting current HTTP request actual timings.

    Filtering dimensions for metrics

    You can apply filters for metrics for external Application Load Balancers.

    Metrics are aggregated for each classic Application Load Balancer and global external Application Load Balancer. You can filter aggregated metrics by the following dimensions for resource.type="http_load_balancer" or resource.type="https_lb_rule" . Note that not all dimensions are available on all metrics.

    Property
    Description
    backend_scope
    The Google Cloud scope ( region or zone ) of the backend service instance group that served the connection.

    If no instance group was available or if the request was served by another entity, you see one of the following values instead of the region or zone of the backend service instance group.

    • FRONTEND_5 xx : an internal error occurred before the GFE could select a backend. The GFE returned 5 xx to the client.
    • INVALID_BACKEND: the GFE couldn't find a healthy backend to assign the request to, so it returned a 5 xx status code to the requestor.
    • NO_BACKEND_SELECTED: either an error or interruption occurred before a backend was selected, a URL redirect occurred, or a classic Application Load Balancer with serverless backends returned a 200 OK response.
    • MULTIPLE_BACKENDS: the request was served by potentially multiple backends. This can happen when Cloud CDN has served the request partially from its cache and has also sent one or more byte range requests to the backend. Use the backend_scope breakdown to visualize each load balancer-to-backend request.

    When this breakdown is chosen, the charts show backend metrics (load balancer-to-backends), not frontend metrics (client-to-load balancer).

    backend_type

    The name of the backend group that served the client's request. Can be INSTANCE GROUP , NETWORK_ENDPOINT_GROUP , or UNKNOWN is returned if the backend wasn't assigned. If no backend group was available or if the request was served by another entity, one of the following values is displayed instead of a backend group.

    • FRONTEND_5XX: an internal error occurred before the GFE could select a backend. The GFE returned 5 xx to the client.
    • INVALID_BACKEND: the GFE couldn't find a healthy backend to assign the request to, so it returned a 5 xx status code to the requestor.
    • NO_BACKEND_SELECTED: either an error or interruption occurred before a backend was selected, a URL redirect occurred, or a classic Application Load Balancer with serverless backends returned a 200 OK response.
    • MULTIPLE_BACKENDS: the request was served by potentially multiple backends. This can happen when Cloud CDN has served the request partially from its cache and has also sent one or more byte range requests to the backend. Use the backend_scope breakdown to visualize each load balancer-to-backend request.
    backend_target_type
    The name of the backend service that served the request. Can be BACKEND_SERVICE , BACKEND_BUCKET , UNKNOWN if the backend wasn't assigned, or NO_BACKEND_SELECTED if an error or interruption occurred before a backend was selected, a URL redirect occurred, or a classic Application Load Balancer with serverless backends returned a 200 OK response.
    matched_url_path_rule
    The URL map path rule that matched the prefix of the HTTP(S) request (up to 50 characters).
    forwarding_rule_name
    The name of the forwarding rule used by the client to send the request.
    url_map_name

    The URL map path rule or route rule configured as part of the URL map key. Can be UNMATCHED or UNKNOWN as fallbacks.

    • UNMATCHED refers to a request that doesn't match any URL path rules, so url_map_name uses the default path rule.
    • UNKNOWN indicates an internal error.
    target_proxy_name
    The name of the target HTTP(S) proxy object referenced by the forwarding rule.
    backend_target_name
    The name of the backend target. The target can be either a backend service or backend bucket. UNKNOWN is returned if a backend wasn't assigned.
    backend_name
    The name of the backend instance group, bucket, or NEG. UNKNOWN is returned if the backend wasn't assigned, or NO_BACKEND_SELECTED if an error or interruption occurred before a backend was selected, a URL redirect occurred, or a classic Application Load Balancer with serverless backends returned a 200 OK response.
    backend_scope_type

    The type of the scope of the backend group. Can be GLOBAL , REGION , ZONE , MULTIPLE_BACKENDS , or NO_BACKEND_SELECTED if an error or interruption occurred before a backend was selected, a URL redirect occurred, or a classic Application Load Balancer with serverless backends returned a 200 OK response, or other possible backend_type outputs.

    MULTIPLE_BACKENDS is used when chunk caching is used. Multiple queries are sent to the same backend for different chunks of data to support a single client request.

    proxy_continent
    Continent of the HTTP(S) GFE that terminated the HTTP(S) connection—for example, America , Europe , Asia
    protocol
    Protocol used by the client, one of HTTP/1.0 , HTTP/1.1 , HTTP/2.0 , QUIC/HTTP/2.0 , UNKNOWN .
    response_code
    The HTTP status code of the request.
    response_code_class
    The HTTP status code class of the request: 200 , 300 , 400 , 500 or 0 for none.
    cache_result
    Cache result for serving HTTP request by proxy: HIT , MISS , DISABLED , PARTIAL_HIT (for a request served partially from cache and partially from backend), or UNKNOWN .
    client_country
    Country of the client that issued the HTTP request—for example, United States or Germany .
    load_balancing_scheme
    The load balancing scheme used. If classic Application Load Balancer is used, the value is EXTERNAL . If global external Application Load Balancer is used, the value is EXTERNAL_MANAGED .

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