Both Cloud Tasks and Pub/Sub can be used to implement message passing and asynchronous integration, but while they function in similar ways, they are not identical. This guide helps you choose the right product for your use case.
Key differences
Pub/Sub and Cloud Tasks differ primarily in whether they use implicit or explicit invocation.
Pub/Sub decouples event publishers from their subscribers. Publishers don't need to know anything about their subscribers. As a result, Pub/Sub offers no control over message delivery beyond guaranteeing it. This supports implicitinvocation: a publisher triggers subscriber execution just by publishing an event.
In contrast, Cloud Tasks aims for explicitinvocation. The publisher retains full control of execution. In particular, a publisher specifies an endpoint where each message is to be delivered.
In addition, Cloud Tasks provides tools for queue and task management unavailable to Pub/Sub publishers, including:
- Specific delivery scheduling
- Delivery rate controls
- Precise configurable retries
- Access and management of individual tasks in a queue
- Task creation deduplication
Detailed feature comparison
| Feature | Cloud Tasks | Pub/Sub |
|---|---|---|
|
Push using webhooks
|
Yes | Yes |
|
At-least-once delivery guarantee
|
Yes | Yes |
|
Configurable retries
|
Yes | Yes |
|
Task/message creation deduplication
|
Yes | No |
|
Scheduled delivery
|
Yes | No |
|
Ordered delivery
|
No, enqueued task order is preserved on a best‑effort basis | Yes, with ordering keys |
|
Explicit rate controls
|
Yes | Pull subscriber clients can implement flow control |
|
Pull using API
|
No | Yes |
|
Batch insert
|
Yes | Yes |
|
Multiple handlers/subscribers per message
|
No | Yes |
|
Task/message retention
|
31 days | Up to 31 days |
|
Maximum size of task/message
|
1MB | 10MB |
|
Maximum delivery rate
|
500 QPS/queue | No upper limit, subject to regional throughput quotas |
|
Geographic availability
|
Regional | Global |
|
Maximum push handler/subscriber processing duration
|
30 minutes (HTTP) 10 minutes (App Engine Standard automatic scaling) 24 hours (App Engine Standard manual or basic scaling) 60 minutes (App Engine Flexible) |
10 minutes for push operations |
|
Number of queues/subscriptions
|
1,000 per project per region, more available through quota increase request | 10,000 per project |
Configurable retry differences
Cloud Tasks offers precise control of task retries, including firm limits on attempts and duration. Pub/Sub focuses on reliable delivery, using exponential backoff and dead-letter queues (DLQ) to manage retries for unacknowledged messages.
| Feature | Cloud Tasks | Pub/Sub |
|---|---|---|
|
Use case focus
|
Ensuring eventual execution of a specific task | Ensuring message delivery to decoupled subscribers |
|
Primary control
|
Queue-level and task-level retry configuration | Subscription-level retry policy and DLQ |
|
Stopping retries
|
Maximum attempts, maximum retry duration | Message acknowledgment, message expiration, or DLQ transfer |
|
Maximum attempts
|
Explicitly configurable | Indirectly through DLQ maximum delivery attempts |
|
Backoff tuning
|
Minimum/maximum backoff, maximum doublings | Minimum/maximum backoff for exponential backoff policy |
|
Indefinite retries
|
Possible if configured, but bounded by maximum task retention limit | Default for unacknowledged messages until expiration, mitigated by DLQ |
