Google Pub/Sub vs Amazon SNS

Google Cloud Pub/Sub and Amazon SNS are both pub/sub messaging services, but Pub/Sub is a more complete solution. Pub/Sub combines what AWS splits across SNS (fan-out) and SQS (persistence) into a single service.

The Key Difference: Persistence

SNS is a notification service. When you publish a message, SNS pushes it to all subscribers immediately. If a subscriber is down, the message may be lost (unless the subscriber is an SQS queue that buffers it).

Pub/Sub stores messages until every subscription acknowledges them. If a subscriber is down for hours, messages accumulate and are delivered when the subscriber reconnects. This built-in persistence means Pub/Sub serves as both SNS and SQS combined.

Delivery Models

Pub/Sub supports both pull and push delivery. Pull subscriptions let consumers poll at their own pace (like SQS). Push subscriptions deliver to HTTPS endpoints (like SNS). This flexibility means one service covers both patterns.

SNS is push-only. For pull-based consumption, you must route SNS to SQS and poll the queue.

Replay and Seek

Pub/Sub supports seeking to a timestamp — replaying messages from a specific point in time within the retention window. SNS has no replay capability at all.

Cross-Cloud Comparison

When comparing cloud messaging services, Pub/Sub's closest AWS equivalent is SNS + SQS together, not SNS alone. This is an important distinction for system design interviews comparing cloud architectures.

For more on messaging patterns, see our pub/sub concepts and interview questions.