Pub/Sub Architecture: Push vs Pull Messaging (When to Use Each)

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Arnav Sharma

Arnav Sharma

Pub/Sub Architecture: Push vs Pull Messaging (When to Use Each)

What is Pub/Sub?

Publish/Subscribe (pub/sub) is a messaging pattern where publishers send messages without knowing who will consume them, and subscribers receive messages without knowing who produced them.

A broker (like Kafka, RabbitMQ, SQS, Redis) usually sits in the middle to handle message delivery.

This decoupling allows systems to communicate asynchronously and scale independently.

Why Pub/Sub?

Pub/Sub solves several common problems in distributed systems:

  • Decoupling – Publishers don’t need to know subscribers.
  • Scalability – Multiple subscribers can process messages independently.
  • Reliability – Messages are queued until consumed (depending on broker).
  • Flexibility – One message can be delivered to many subscribers (fanout).

When Pub/Sub?

Use pub/sub when:

  • You want event-driven architecture (e.g., user signup triggers emails, notifications).
  • You need to scale workers dynamically.
  • You need loose coupling between microservices.
  • You need to ensure asynchronous processing (background jobs, pipelines).

Don’t use pub/sub when you need strict request/response (synchronous API calls).

How Pub/Sub (Types)

There are two main ways subscribers receive messages:

:small_blue_diamond: Push-based Pub/Sub

  • The broker pushes messages directly to subscribers.
  • Subscribers don’t need to poll.
  • Example: RabbitMQ pushes messages to consumers.

:white_check_mark: Low latency

:white_check_mark: Easy subscriber logic

:cross_mark: Risk of overwhelming slow subscribers

:small_blue_diamond: Pull-based Pub/Sub

  • Subscribers request (pull) messages from the broker when ready.
  • Example: AWS SQS requires consumers to poll for messages.

:white_check_mark: Subscribers control pace (backpressure handling)

:white_check_mark: Reliable retries

:cross_mark: Slightly higher latency due to polling

Comparison

Feature Push-based Pub/Sub Pull-based Pub/Sub
Delivery model Broker delivers Subscriber requests
Latency Lower (instant delivery) Higher (polling delay)
Backpressure control Harder Easier
Subscriber logic Simple (just receive) More complex (polling)
Example tech RabbitMQ, Redis Pub/Sub AWS SQS, Kafka

Which Tech Uses Which One and How?

:rabbit: RabbitMQ (Push-based)

  • Consumers register with a queue.
  • RabbitMQ pushes messages to consumers.
  • You can configure prefetch to avoid overloading consumers.
  • Great for real-time apps (chat, IoT, financial trading).

:cloud: AWS SQS (Pull-based)

  • Messages are stored in SQS queues.
  • Consumers must poll SQS to fetch them.
  • Can use long polling for efficiency.
  • Great for cloud pipelines, serverless apps, microservices decoupling.

Real World Example

Imagine an e-commerce platform:

  • A customer places an order.
  • Publisher: Order service emits an order_created event.
  • Push-based: A notification service instantly gets the event via RabbitMQ and sends an SMS.
  • Pull-based: A reporting service pulls events from SQS at its own pace to update sales dashboards.

Conclusion

Both pull-based and push-based pub/sub models have their strengths:

  • Push-based is best when you need low latency, real-time delivery (RabbitMQ, Redis Pub/Sub).
  • Pull-based is best when you need scalability, reliability, and backpressure control (AWS SQS, Kafka).

:backhand_index_pointing_right: The right choice depends on your use case:

  • For real-time notifications, go with push.
  • For background processing or analytics, go with pull.

In modern architectures, teams often combine both models—push for immediate actions, pull for batch or heavy workloads.