Both Cloud Tasks and Pub/Sub can be used to implement message passing and asynchronous integration. Although they are conceptually similar, each is designed for different set of use cases. This page helps you choose the right product for your use case.
The core difference between Pub/Sub and Cloud Tasks is in the notion of implicit vs. explicit invocation.
Pub/Sub aims to decouple publishers of events and subscribers to those events. Publishers do not need to know anything about their subscribers. Therefore, Pub/Sub gives publishers no control over the delivery of the messages save for the guarantee of delivery. In this way, Pub/Sub supports implicit invocation: a publisher implicitly causes the subscribers to execute by publishing an event.
By contrast, Cloud Tasks is aimed at explicit invocation where the publisher retains full control of execution. In particular, a publisher specifies an endpoint where each message is to be delivered.
Overall Cloud Tasks are appropriate for use cases where a task producer needs to defer or control the execution timing of a specific webhook or remote procedure call. Pub/Sub is optimal for more general event data ingestion and distribution patterns where some degree of control over execution can be sacrificed.
Detailed feature comparison
|Feature||Cloud Tasks||Cloud Pub/Sub|
|Push via webhooks||Yes||Yes|
|At least once delivery guarantee||Yes||Yes|
|Task creation deduplication||Yes||No|
|Explicit rate controls||Yes||No (Subscriber clients can implement flow control)|
|Pull via API||No||Yes|
|Multiple handlers/subscribers per message||No||Yes|
|Task/message retention||30 days||Up to 7 days|
|Max size of task/message||100KB||10MB|
|Max delivery rate||500 qps/queue||No upper limit|
|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 per project||1,000/project, more available via quota increase request||10,000/project|