Event sourcing in Elixir

Chronicle is an open-source (MIT) event-sourcing database and processing runtime, and cratis_chronicle is its idiomatic Elixir client. It exposes OTP-native constructs — use Chronicle.EventType, use Chronicle.ReadModel, use Chronicle.Reactor, use Chronicle.Reducer, and use Chronicle.Seeder — plus model-bound constraints, context-aware appends with process-scoped identity, correlation, and causation metadata, optimistic concurrency, transactions, jobs and webhooks, and automatic reconnection with exponential backoff. The client supervises a connection to the Chronicle kernel as part of your application’s supervision tree.

With event sourcing, every state change is captured as an immutable event rather than an update in place. Chronicle stores those events, and read models are derived from them — declared model-bound projections execute server-side, or you can fold events into read models in your own process with a reducer.

The event store is not BEAM-only: Chronicle’s kernel exposes a language-agnostic gRPC/protobuf boundary, and the same store is reachable from the .NET, TypeScript, and Kotlin/Java clients as well. Storage is pluggable — MongoDB by default, with PostgreSQL, SQL Server, SQLite, and in-memory providers implemented in the kernel.

Install

mix.exs

defp deps do
  [
    {:cratis_chronicle, "~> 0.0"}
  ]
end

A taste

An event type, a supervised client, and an append — from the client repository’s quick example:

defmodule MyApp.Events.AccountOpened do
  use Chronicle.EventType, id: "account-opened-v1"
  defstruct [:account_id, :owner_name, :initial_balance]
end

defmodule MyApp.Application do
  use Application

  def start(_type, _args) do
    children = [
      {Chronicle.Client,
        connection_string: "chronicle://localhost:35000",
        event_store: "my-app",
        otp_app: :my_app}
    ]

    Supervisor.start_link(children, strategy: :one_for_one)
  end
end

# Append an event
:ok = Chronicle.append("account-42", %MyApp.Events.AccountOpened{
  account_id: "account-42",
  owner_name: "Alice",
  initial_balance: 1000
})

For a local kernel to append to, the development Docker image is the quickest path: docker run -p 35000:35000 cratis/chronicle:latest-development.

Where to go next

Elixir client docs Installation, connection setup, OTP integration, and the full Elixir API surface.

Get started with Chronicle Run Chronicle locally and build your first event-sourced feature.

Chronicle.Elixir on GitHub The Elixir client repository — open source, MIT licensed.

cratis_chronicle on Hex The Elixir client package for Chronicle.

Looking for another language? See Chronicle in your language for the .NET, TypeScript, and Kotlin/Java clients.