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Chief of State

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Overview

Chief-of-state (COS) is an Open Source clustered persistence tool for building event sourced applications. COS supports CQRS and event-sourcing through simple, language-agnostic interfaces via gRPC, and it allows developers to describe their schema with Protobuf. Under the hood, COS leverages Akka to scale out and guarantee performant, reliable persistence.

Chief-of-state was built by Namely with the following principles:

  • Wire format should be the same as persistence
  • Scaling should not require re-architecture
  • Developers shouldn't face race conditions or database locks
  • Rules should be enforced with interfaces
  • Event sourcing is valuable, but challenging to implement
  • An ideal event-sourcing datastore would offer random access by key, streaming, and atomic writes

Anatomy of a chief-of-state app

Developers implement two gRPC interfaces: a write handler for building state and, optionally, many read handlers for reacting to state changes.

Architecture Diagram

Chief Of State Service

The main entry point of a chief-of-state based application is the Service. Developers will interact with chief of state via:

  • ProcessCommand is used by the application to send commands to process via Write Handler.
  • GetState is used by the application to retrieve the current state of a persistent entity

Write Handler

Developers describe state mutations by implementing two RPC’s in the WriteSideHandlerService:

  • HandleCommand accepts a command and the prior state of an entity and returns an Event. For example, given a command to UpdateUserEmail and a User, this RPC might return UserEmailUpdated.
  • HandleEvent accepts an event and the prior state of an entity and returns a new state. For example, given a UserEmailUpdated event and a User, this RPC would return a new User instance with the email updated.

Read Handler

In response to state mutations, COS is able to send changes to many ReadSideHandlerService implementations, which may take any action. COS guarantees at-least-once delivery of events and resulting state to each read side in the order they were persisted.

Some potential read side handlers might:

  • Write state changes to a special data store like elastic
  • Publish changes to kafka topics
  • Send notifications to users in response to specific events

Features

  • Journal and Snapshot serialization using google protocol buffer message format
  • Preconfigured Akka clustering and domain entity sharding with the split-brain-resolver algorithm
  • Automatic caching and entity passivation
  • Automatic configuration of postgres storage on boot
  • Opentelemetry integration for tracing and prometheus metrics
  • Direct integration to Kubernetes to form a cluster

Documentation

The following docs are available:

Community

You can join these groups and chat to discuss and ask Chief Of State related questions on:

Gitter Github: namely/chief-of-state

Contribution

Contributions are welcome!

If you see an issue that you'd like to see fixed, the best way to make it happen is to help out by submitting a pull request implementing it. To test your implementation locally follow the steps below:

Locally build / test

# install earthly cli
brew install earthly/earthly/earthly (for mac users)

# locally build the image
earthly +build-image

# run tests
earthly -P --no-output +test-local

License

License: MIT

Sample Projects

Python