Google Cloud Pub/Sub

• Cloud Pub/Sub is a fully-managed real-time messaging service for event driven systems that allows you to send and receive messages between independent applications.

Features

• Capable of global message routing to simplify multi-region systems.
• Synchronous, cross-zone message replication and per-message receipt tracking ensure at-least-once delivery at any scale. Pub/Sub delivers each message at least once, so the Pub/Sub service might redeliver messages.
• You can declare independent quota and billing for publishers and subscribers.
• Cloud Pub/Sub doesn’t have shards or partitions. You just need to set your quota, publish, and consume.

Key Concepts

• Topic
  • It is a named resource to which publishers send messages.
• Subscription
  • Is a named resource representing the stream of messages from a specific topic, to be sent to the subscribing application.
• Message
  • The combination of data and attributes that a publisher sends to a topic and is eventually sent to subscribers.
• Message attribute
  • A key-value pair that a publisher can define for a message.

Publisher-subscriber relationships

• A publisher application creates and sends messages to a topic.
• Subscriber applications then create a subscription to a topic to receive messages from the topic.
• Communication can be
  • one-to-many
  • many-to-one
  • many-to-many

Pricing

• Pub/Sub pricing is calculated based upon monthly data volumes:
  • Message ingestion and delivery
  • Snapshots and retained acknowledged messages
• The first 10 GB of data per month is offered free of charge.

References:
https://cloud.google.com/pubsub
https://cloud.google.com/pubsub/docs/overview