A Hammer (v7+) backend for clustered Redis, built on eredis_cluster.

defmodule MyApp.RateLimit do
  use Hammer, backend: Hammer.EredisCluster
end

# The cluster is connected elsewhere (e.g. the :eredis_cluster app env
# `init_nodes`) — just start the limiter:
MyApp.RateLimit.start_link([])

# Or let the limiter establish the connection itself:
MyApp.RateLimit.start_link(
  servers: [{"127.0.0.1", 7001}, {"127.0.0.1", 7002}],
  options: [username: "myuser", password: "mypassword"]
)

{:allow, _count} = MyApp.RateLimit.hit("user_123", _scale_ms = :timer.minutes(1), _limit = 10)

Compile-time options (use Hammer, backend: Hammer.EredisCluster, ...)

• :cluster — the eredis_cluster name to run commands against (default :eredis_cluster_default, eredis_cluster's default cluster).
• :prefix — Redis key prefix (default: the limiter module name).
• :algorithm — only :fix_window is supported.

Runtime options (start_link/1)

• :servers — list of {host, port} seed nodes. Omit when the cluster connection is managed elsewhere (e.g. config :eredis_cluster, init_nodes: ...).
• :options — keyword list forwarded to eredis (:username, :password, ...).

Keys

Redis keys are prefix:{key}:window. The {key} hash tag pins every window of a given key to the same cluster slot, preserving slot affinity for multi-window operations. Keys must be strings — this backend serializes them into Redis key names (v7.1's term() keys are not supported here).

Unlike the v6 backend (Hammer.Backend.EredisCluster), there is no process in the request path: hit/3,4 and friends talk to eredis_cluster's pools directly. The process started by start_link/1 only establishes the cluster connection and holds no per-request state.