Laminas ServiceManager and Docker: Configuration Cache Placement

Answer

For Laminas ServiceManager running in Docker, do not bake a merged configuration cache into an immutable image when the configuration depends on runtime environment variables. The supported pattern is runtime cache with a writable location, or cache disabled for fully stateless portability. Build-time cache generation is only safe for truly static configuration.

Confirmed facts

• Laminas ServiceManager merges global and local PHP config arrays at bootstrap. Merging is performed by the application bootstrap, not by ServiceManager itself.
• The Laminas Config component provides a ConfigCache helper. Caching can be disabled by setting config_cache_enabled to false in global config.
• The cache file must be writable by the PHP process. If the directory is not writable the bootstrap fails.

Likely explanation and practical guidance

The uncertainty you describe is real: immutable image layers conflict with runtime env vars. If the cache is generated at build time, any change to environment variables after the image is built will not be reflected until the image is rebuilt. If the cache is persisted in a volume, the image remains portable and the cache can be invalidated without a rebuild.

Assumption: you are using Laminas Config with merged autoload config and optionally Laminas\Config\ConfigCache. Version-specific behavior is not verified here; confirm against the project documentation for your Laminas version.

Steps for this case

1. Decide static vs dynamic config.
2. If config is static at build time:

• Generate cache in Dockerfile: RUN php bin/build-config-cache.php
• Ensure cache directory is inside the image and the web user can read it.

1. If config contains runtime environment variables:

• Mount a Docker volume for the cache directory, e.g. /var/www/html/cache.
• Clear or regenerate the cache on container start before the first request.
• Make the cache key depend on relevant env vars or simply remove the cache file on startup to avoid stale data.

1. Development: disable cache.

• Set config_cache_enabled => false in config/autoload/local.php to keep containers fully stateless.

Verification checks:

• Confirm the cache directory is writable by the PHP user inside the container.
• Start container with a changed env var, clear cache on startup, and verify ServiceManager loads the new value.

One missing diagnostic detail that changes the recommendation: Is your merged configuration fully static at build time, or does it depend on runtime environment variables such as database host, API keys, or feature flags? If dynamic, the volume + invalidate-on-start pattern is required; if static, build-time generation is acceptable.