Access flow logs

This page describes how to access flow logs by using Cloud Logging.

Access flow logs in the Logs Explorer

VPC Flow Logs writes logs to the Google Cloud project of the log reporter. You can view flow logs in the Logs Explorer . VPC Flow Logs uses the following logs to collect log entries:

• The compute.googleapis.com/vpc_flows log collects log entries for subnets. View this log if you enabled VPC Flow Logs by using the Compute Engine API .
• For all other VPC Flow Logs configurations, view the networkmanagement.googleapis.com/vpc_flows log. This log collects log entries for Virtual Private Cloud (VPC) networks ( Preview ), subnets ( Preview ), VLAN attachments for Cloud Interconnect, and Cloud VPN tunnels.

Configure IAM

To configure access control for logging, see the access control guide for Logging .

View flow logs by using resource filters

To view flow logs in a Google Cloud project by using resource filters, see the following sections. You can also view these logs by using Logs Explorer queries, as described in Filter flow logs by using queries .

View flow logs for all subnets ( compute.googleapis.com/vpc_flows )

1. In the Google Cloud console, go to the Logs Explorerpage.

   Go to Logs Explorer

2. Click All resources.

3. In the Select resourcelist, click Subnetworkand then click Apply.

4. Click All log names.

5. In the Select log nameslist, find Compute Engine, click vpc_flows, and then click Apply.

View flow logs for a specific subnet ( compute.googleapis.com/vpc_flows )

1. In the Google Cloud console, go to the Logs Explorerpage.

   Go to Logs Explorer

2. Click All resources.

3. In the Select resourcelist, click Subnetwork.

4. In the Subnetwork IDlist, select the subnet and then click Apply.

5. Click All log names.

6. In the Select log nameslist, find Compute Engine, click vpc_flows, and then click Apply.

View flow logs for all resources ( networkmanagement.googleapis.com/vpc_flows )

1. In the Google Cloud console, go to the Logs Explorerpage.

   Go to Logs Explorer

2. Click All resources.

3. In the Select resourcelist, click VPC Flow Logs Configand then click Apply.

View flow logs for a specific configuration ( networkmanagement.googleapis.com/vpc_flows )

1. In the Google Cloud console, go to the Logs Explorerpage.

   Go to Logs Explorer

2. Click All resources.

3. In the Select resourcelist, click VPC Flow Logs Configand select the VPC Flow Logs configuration that you want to view.

4. Click Apply.

Filter flow logs by using queries

1. In the Google Cloud console, go to the Logs Explorerpage.

   Go to Logs Explorer

2. If you don't see the query editor field in the Querypane, click the Show querytoggle.

3. In the query editor field, enter a query:

   • If you enabled VPC Flow Logs for a subnet by using the Compute Engine API, to view flow logs, the query must target compute.googleapis.com . For example, enter the following query, replacing PROJECT_ID with your Google Cloud project ID and SUBNET_NAME with your subnet:

     resource.type="gce_subnetwork"
     logName="projects/ PROJECT_ID 
     /logs/compute.googleapis.com%2Fvpc_flows"
     resource.labels.subnetwork_name=" SUBNET_NAME 
     "

   • For all other queries, the query must target networkmanagement.googleapis.com . For example, to view flow logs for a specific source Cloud VPN tunnel, enter the following query:

     resource.type="vpc_flow_logs_config"
     logName="projects/ PROJECT_ID 
     /logs/networkmanagement.googleapis.com%2Fvpc_flows"
     jsonPayload.reporter="src_gateway"
     labels.target_resource_name="projects/ PROJECT_ID 
     /regions/ REGION 
     /vpnTunnels/ NAME 
     "

     Replace the following:

     • PROJECT_ID : the Google Cloud project ID
     • REGION : the region of the Cloud VPN tunnel
     • NAME : the name of the Cloud VPN tunnel

     For more examples of queries that you can run to view your flow logs, see Examples of Logs Explorer queries for VPC Flow Logs .

4. Click Run query.

Examples of Logs Explorer queries for VPC Flow Logs

The following table provides examples of Logs Explorer queries that you can run to view your flow logs in a Google Cloud project.

The examples in the Queries for the networkmanagement.googleapis.com/vpc_flows section assume that each resource is logged by a single VPC Flow Logs configuration. If you use multiple VPC Flow Logs configurations per resource, specify the configuration that you want to query to exclude duplicate logs from the query results. You can also specify multiple configurations in a query.

resource.type=("gce_subnetwork" OR "vpc_flow_logs_config")
logName=("projects/ PROJECT_ID 
/logs/compute.googleapis.com%2Fvpc_flows" OR
"projects/ PROJECT_ID 
/logs/networkmanagement.googleapis.com%2Fvpc_flows")

resource.type="gce_subnetwork"
logName="projects/ PROJECT_ID 
/logs/compute.googleapis.com%2Fvpc_flows"

resource.type="gce_subnetwork"
logName="projects/ PROJECT_ID 
/logs/compute.googleapis.com%2Fvpc_flows"
resource.labels.subnetwork_name=" SUBNET_NAME 
"

resource.type="gce_subnetwork"
logName="projects/ PROJECT_ID 
/logs/compute.googleapis.com%2Fvpc_flows"
(jsonPayload.src_instance.vm_name=" VM_NAME 
" OR
jsonPayload.dest_instance.vm_name=" VM_NAME 
")

resource.type="gce_subnetwork"
logName="projects/ PROJECT_ID 
/logs/compute.googleapis.com%2Fvpc_flows"
ip_in_net(jsonPayload.connection.dest_ip, SUBNET_RANGE 
)

resource.type="gce_subnetwork"
logName="projects/ PROJECT_ID 
/logs/compute.googleapis.com%2Fvpc_flows"
(jsonPayload.src_gke_details.cluster.cluster_name=" CLUSTER_NAME 
" OR
jsonPayload.dest_gke_details.cluster.cluster_name=" CLUSTER_NAME 
")

resource.type="gce_subnetwork"
logName="projects/ PROJECT_ID 
/logs/compute.googleapis.com%2Fvpc_flows" AND
jsonPayload.reporter="SRC" AND
jsonPayload.src_vpc.subnetwork_name=" SUBNET_NAME 
" AND
(jsonPayload.dest_vpc.subnetwork_name!=" SUBNET_NAME 
"
 OR NOT jsonPayload.dest_vpc.subnetwork_name:*)

resource.type="gce_subnetwork"
logName="projects/ PROJECT_ID 
/logs/compute.googleapis.com%2Fvpc_flows" AND
jsonPayload.reporter="SRC" AND
jsonPayload.src_vpc.vpc_name=" VPC_NAME 
" AND
(jsonPayload.dest_vpc.vpc_name!=" VPC_NAME 
" OR NOT jsonPayload.dest_vpc:*)

resource.type="gce_subnetwork"
logName="projects/ PROJECT_ID 
/logs/compute.googleapis.com%2Fvpc_flows"
jsonPayload.connection.dest_port= PORT 
jsonPayload.connection.protocol= PROTOCOL 

resource.type="gce_subnetwork"
logName="projects/ PROJECT_ID 
/logs/compute.googleapis.com%2Fvpc_flows"
jsonPayload.connection.dest_port=( PORT1 
OR PORT2 
)
jsonPayload.connection.protocol= PROTOCOL 

resource.type="vpc_flow_logs_config"
logName="projects/ PROJECT_ID 
/logs/networkmanagement.googleapis.com%2Fvpc_flows"

resource.type="vpc_flow_logs_config"
logName="projects/ PROJECT_ID 
/logs/networkmanagement.googleapis.com%2Fvpc_flows"
resource.labels.name=" CONFIG_NAME 
"

resource.type="vpc_flow_logs_config"
logName="projects/ PROJECT_ID 
/logs/networkmanagement.googleapis.com%2Fvpc_flows"
jsonPayload.reporter="src_gateway"
labels.target_resource_name="projects/ PROJECT_ID 
/regions/ REGION 
/vpnTunnels/ NAME 
"

resource.type="vpc_flow_logs_config"
logName="projects/ PROJECT_ID 
/logs/networkmanagement.googleapis.com%2Fvpc_flows"
jsonPayload.reporter="dest_gateway"
jsonPayload.dest_gateway.type="INTERCONNECT_ATTACHMENT"

resource.type="vpc_flow_logs_config"
logName="projects/ PROJECT_ID 
/logs/networkmanagement.googleapis.com%2Fvpc_flows"
jsonPayload.reporter="dest_gateway"
jsonPayload.dest_gateway.type="INTERCONNECT_ATTACHMENT"
jsonPayload.dest_gateway.location=" REGION 
"

Replace the following:

• PROJECT_ID : the project ID
• SUBNET_NAME : the name of the subnet
• VM_NAME : the name of the VM
• SUBNET_RANGE : a CIDR range, such as 192.168.1.0/24
• CLUSTER_NAME : the name of the GKE cluster
• VPC_NAME : the name of the VPC network
• PORT1 and PORT2 : the destination ports
• PROTOCOL : the communication protocol
• CONFIG_NAME : the name of the VPC Flow Logs configuration
• REGION : the region of the VLAN attachment or Cloud VPN tunnel
• NAME : the name of the Cloud VPN tunnel

Route logs to BigQuery, Pub/Sub, and custom targets

You can route flow logs from Logging to a destination of your choice as described in the Routing and storage overview in the Logging documentation. Refer to the previous section for example filters.

Troubleshooting

No vpc_flows appear in Logging for the gce_subnetwork resource

• Confirm that logging is enabled for the given subnet.
• VPC flows are only supported for VPC networks. If you have a legacy network , you don't see any logs.
• In Shared VPC networks, logs only appear in the host project, not the service projects. Make sure that you look for the logs in the host project.
• Logging exclusion filters block specified logs. Make sure that there are no exclusion rules that discard VPC Flow Logs:
  1. Go to Log router .
  2. In the more_vert More actionsmenu for your logging bucket, click View sink details.
  3. Make sure that there are no exclusion rules that might discard VPC Flow Logs.
• Use the Google Cloud CLI or API to determine if a log filtering configuration is filtering all the traffic in a given subnet. For example, if filterExpr is set to false , you don't see any logs.

No RTT or byte values on some of the logs

• RTT measurements may be missing if not enough packets were sampled to capture RTT. This is more likely to happen for low volume connections.
• RTT values are available only for TCP flows reported from VMs.
• Some packets are sent with no payload. If header-only packets were sampled, the bytes value will be 0.

Some flows are missing

• Ingress packets are sampled after ingress VPC firewall rules . Make sure that there aren't any ingress firewall rules that deny the packets that you expect to be logged. If you're not sure whether VPC firewall rules are blocking ingress packets, you can enable Firewall Rules Logging and inspect the logs.
• Only TCP, UDP, ICMP, ESP, and GRE protocols are supported. VPC Flow Logs does not support any other protocols.
• Logs are sampled . Some packets in very low volume flows might be missed.

Missing GKE annotations in some logs

Make sure that your GKE cluster is a supported version .

Missing logs for some GKE flows

Make sure Intranode visibility is enabled in the cluster. Otherwise, flows between Pods on the same node are not logged.

What's next

• View Logging documentation
• View Logging sinks documentation
• Analyze flow logs in Flow Analyzer