Ansible "couldn't resolve module/action" collection not installed in CI

Ansible could not map a fully qualified collection name to a module because the collection that provides it is not installed on the runner. A clean CI image only ships ansible-core builtins, so external collections must be installed first.

What this error means

The run fails with "ERROR! couldn't resolve module/action 'community.general.timezone'. This often indicates a misspelling, missing collection, or incorrect module path." even though the playbook is correct.

ansible

ERROR! couldn't resolve module/action 'community.docker.docker_container'. This
often indicates a misspelling, missing collection, or incorrect module path.

Common causes

The collection is not installed on the runner

ansible-core ships only builtins, so collections like community.general or community.docker must be installed before the play runs.

No requirements.yml driving the install

Without a galaxy requirements file the CI job never installs the collection the playbook depends on.

How to fix it

Install collections from requirements.yml

List required collections in requirements.yml.
Run ansible-galaxy collection install before the playbook.
Re-run so the FQCN resolves.

requirements.yml

# requirements.yml
collections:
  - name: community.docker
    version: ">=3.0.0"

Install as a CI step

Install the collections before the playbook step so the modules are present.

.github/workflows/ci.yml

ansible-galaxy collection install -r requirements.yml

How to prevent it

Pin required collections in requirements.yml and install them in CI.
Cache the Galaxy collection path between runs.
Use FQCNs and keep the providing collection installed.