Yoke Launcher — Automatic Release Rebuild

The ./yoke executable is a thin Bash launcher that boots the Yoke OTP release. Unlike a static launcher that merely invokes an existing release, yoke keeps the release in sync with the working tree by re-assembling it with mix release --overwrite whenever the sources have changed.

Why auto-rebuild?

OTP releases are immutable snapshots of your application. If you edit Elixir source files but the release is not rebuilt, ./yoke silently runs the old code. This is a common source of confusion during development:

# 1. Build a release once
./yoke --env dev

# 2. Edit lib/yoke/cli/repl.ex

# 3. Without auto-rebuild, ./yoke would keep running the OLD compiled code
./yoke --env dev   # <-- now re-assembles with --overwrite automatically

When does the launcher rebuild?

The launcher rebuilds the selected release when any of the following is true:

1. The release binary is missing — first run, or after a clean checkout.
2. A watched source file is newer than the release binary — any file under:
• lib/**/*.{ex,exs}

• config/**/*.exs

• priv/**/*

• mix.exs

• mix.lock

1. YOKE_REBUILD=1 is set — forces a rebuild regardless of timestamps.

The comparison uses file modification timestamps. If the newest source file's mtime is strictly greater than the release binary's mtime, the release needs a rebuild.

How it works

Two helper functions are defined in the script:

release_needs_build

Returns exit code 0 (rebuild needed) or 1 (up to date). It checks:

• whether the release binary rel_bin is executable;
• the YOKE_REBUILD environment variable;
• whether the newest watched source file is newer than rel_bin .

if release_needs_build "$PROD_REL"; then
  build_release "prod"
fi

build_release

Assembles the release for the given Mix environment (e.g. prod or dev ):

build_release "prod"
# -> rm -rf _build/prod/rel/yoke
# -> MIX_ENV=prod mix release yoke --overwrite

It always passes --overwrite so an existing release directory is replaced rather than merged, and it removes the stale _build//rel/yoke directory first to guarantee a deterministic build.

Environment targets

Configuration variables

Testing

The release freshness logic is covered by test/yoke_release_test.sh :

bash test/yoke_release_test.sh

The test exercises the release_needs_build and build_release functions in isolation against temporary fixture trees, verifying:

1. no rebuild when all sources are older than the release;
2. rebuild when a source file is newer than the release;
3. rebuild when the release binary is missing;
4. YOKE_REBUILD=1 forces a rebuild;
5. build_release invokes mix release yoke --overwrite .