Symfony Flex not running during composer install in CI

By Daniel Zoghalchali·Latchkey

Composer 2 blocks plugins unless allow-listed. If symfony/flex is not allowed, it silently does not run, so recipes that create config files and .env entries are never applied, leading to missing-config errors later in CI.

What this error means

composer install prints "symfony/flex ... plugin was skipped because it is not in allow-plugins", and later steps fail because recipe-provided config or env keys are absent.

symfony/flex contains a Composer plugin which is currently not in your allow-plugins config.
See https://getcomposer.org/allow-plugins
Do you trust "symfony/flex" to execute code ... [y,n,d,?]

Common causes

Flex is not in composer allow-plugins

Composer 2 requires plugins to be explicitly trusted. Without the allow entry, Flex is skipped in non-interactive CI and its recipes never run.

Install runs with plugins disabled

A --no-plugins install (or a hardened CI setting) prevents Flex from executing, so recipe side effects are missing.

How to fix it

Allow the Flex plugin in composer.json

1. Add symfony/flex to config.allow-plugins.
2. Commit composer.json so CI trusts the plugin non-interactively.
3. Re-run composer install.

{
  "config": {
    "allow-plugins": {
      "symfony/flex": true,
      "symfony/runtime": true
    }
  }
}

Do not disable plugins in the CI install

Install with plugins enabled so Flex can apply recipes; only skip dev dependencies if you intend to.

composer install --prefer-dist --no-interaction --no-progress

How to prevent it

• Keep symfony/flex in allow-plugins so it runs everywhere non-interactively.
• Avoid --no-plugins in CI unless you deliberately want recipes skipped.
• Commit recipe-generated config so the app does not depend on Flex at install time.

Frequently asked questions

Related guides

References

• Composer documentation
• GitHub Actions documentation