RedisServerWrapper

Manage redis-server processes from Elixir -- single instances, clusters, and sentinel topologies with GenServer lifecycle management.

No Docker required. Just redis-server and redis-cli on your PATH.

Installation

Add redis_server_wrapper to your list of dependencies in mix.exs:

def deps do
  [
    {:redis_server_wrapper, "~> 0.7"}
  ]
end

Prerequisites

You need redis-server and redis-cli installed and available on your PATH.

# macOS
brew install redis

# Ubuntu/Debian
sudo apt-get install redis-server

# Verify
redis-server --version

Quick Start

Single Server

{:ok, server} = RedisServerWrapper.start_server(port: 6400, password: "secret")

RedisServerWrapper.Server.ping(server)
#=> true

RedisServerWrapper.Server.run(server, ["SET", "key", "value"])
#=> {:ok, "OK"}

RedisServerWrapper.Server.run(server, ["GET", "key"])
#=> {:ok, "value"}

RedisServerWrapper.Server.stop(server)

Cluster

{:ok, cluster} = RedisServerWrapper.start_cluster(masters: 3, base_port: 7100)

RedisServerWrapper.Cluster.healthy?(cluster)
#=> true

RedisServerWrapper.Cluster.node_addrs(cluster)
#=> ["127.0.0.1:7100", "127.0.0.1:7101", "127.0.0.1:7102"]

RedisServerWrapper.Cluster.stop(cluster)

Sentinel

{:ok, sentinel} = RedisServerWrapper.start_sentinel(
  master_port: 6390,
  replicas: 2,
  sentinels: 3
)

RedisServerWrapper.Sentinel.healthy?(sentinel)
#=> true

RedisServerWrapper.Sentinel.master_addr(sentinel)
#=> "127.0.0.1:6390"

RedisServerWrapper.Sentinel.stop(sentinel)

Persistent Instances (Manager)

The Manager tracks instances across IEx sessions using a JSON state file:

RedisServerWrapper.Manager.start_basic(name: "dev-redis", port: 6400)
#=> {:ok, %{name: "dev-redis", url: "redis://:password@127.0.0.1:6400", ...}}

RedisServerWrapper.Manager.list()
#=> [%{name: "dev-redis", type: :basic, ...}]

RedisServerWrapper.Manager.stop("dev-redis")

Managed Process Lifecycle

Server.start_link/1 accepts a :managed option controlling how the redis-server OS process is tied to the BEAM:

• managed: true (default) - redis-server runs as a foreground Port. Teardown runs in terminate/2, which OTP skips on a :brutal_kill supervisor shutdown or a hard BEAM death (SIGKILL, OOM), so the OS process can be stranded on those paths, keeping its port bound.

• managed: :forcola - redis-server runs in the foreground under a Forcola.Daemon, whose Rust shim guarantees the OS process group is killed and confirmed dead on owner death or supervisor shutdown, including the paths where terminate/2 never runs. This requires the optional dependency and is opt-in:

  # mix.exs
  {:forcola, "~> 0.3"}
  

  {:ok, server} = RedisServerWrapper.Server.start_link(port: 6400, managed: :forcola)
  

  Without :forcola on the path, start_link returns {:error, :forcola_not_available}. Forcola is POSIX-only and ships precompiled, SHA256-verified shim binaries, so it needs no Rust toolchain at build time.

• managed: false - redis-server daemonizes independently; the caller owns the OS process lifecycle.

Custom Modules

Use :loadmodule to load one or more Redis modules. A plain path is enough for a module with defaults; use {path, [args]} when it takes load-time arguments. The structured form quotes every path and argument safely in the generated redis.conf.

module_path = System.fetch_env!("EVENT_STREAM_MODULE")

{:ok, server} =
  RedisServerWrapper.start_server(
    port: 6460,
    loadmodule: [
      {module_path, ["events", "expired,set", "maxlen", "1000"]}
    ]
  )

RedisServerWrapper.Server.run(server, ["MODULE", "LIST"])

For a cluster, the same modules are loaded into every node. For a Sentinel topology, they are loaded into the master and every replica (not the Sentinel control processes):

RedisServerWrapper.start_cluster(
  base_port: 7100,
  loadmodule: [
    {module_path, ["cluster-streams", "per-node"]}
  ]
)

The original raw directive form remains supported for compatibility, such as loadmodule: ["/path/module.so events expired"], but the structured form is recommended when arguments are present.

For a complete event-stream demo using redis-event-stream-module:

EVENT_STREAM_MODULE=/absolute/path/to/libredis_event_stream_module.so \
  mix run examples/event_stream.exs

Configuration

All Redis configuration directives can be set via the Config struct options. Use the :extra option as an escape hatch for any directive not covered by the typed fields:

RedisServerWrapper.start_server(
  port: 6400,
  password: "secret",
  maxmemory: "256mb",
  maxmemory_policy: "allkeys-lru",
  extra: [
    {"notify-keyspace-events", "KEA"},
    {"hz", "100"}
  ]
)

Chaos / Fault Injection

The Chaos module provides fault injection primitives for testing resilience:

alias RedisServerWrapper.{Chaos, Cluster, Server}

{:ok, cluster} = RedisServerWrapper.start_cluster(
  masters: 3,
  replicas_per_master: 1,
  base_port: 7100
)

# Kill the master owning a key's hash slot
{:ok, killed} = Chaos.kill_master(cluster, "user:123")

# Kill by slot number
{:ok, killed} = Chaos.kill_master(cluster, 5000)

# Freeze a node (SIGSTOP) and resume later
{:ok, os_pid} = Chaos.freeze_node(server)
# ... test timeout/retry behavior ...
Chaos.resume_node(os_pid)

# Freeze with automatic resume after a duration
Chaos.pause_node(server, 5_000)

# Simulate a network partition
nodes = Cluster.nodes(cluster)
{active, isolated} = Enum.split(nodes, 2)
{:ok, frozen_pids} = Chaos.partition(cluster, [active, isolated])

# Recover all frozen nodes
Chaos.recover(frozen_pids)

# Other tools
Chaos.slow_down(server, 2_000)        # CLIENT PAUSE
Chaos.flushall(server)                 # wipe all data
Chaos.fill_memory(server, 10_000)      # fill with 1KB dummy keys
Chaos.trigger_save(server)             # force BGSAVE
Chaos.random_kill(cluster)             # kill a random node
Chaos.trigger_failover(replica)        # CLUSTER FAILOVER on a replica

Use Cases

• Testing -- spin up real Redis instances in ExUnit setup/teardown
• Development -- run Redis alongside your app without system services
• CI -- no Docker layer needed, just install redis-server
• Cluster/Sentinel testing -- create full topologies in a single function call
• Resilience testing -- fault injection with the Chaos module (kill nodes, simulate partitions, inject latency)

License

Licensed under either of

• MIT License
• Apache License, Version 2.0

at your option. See LICENSE for details.