Reuse a service's configuration across Compose files or within the same file using the extends attribute
domain: docs.docker.com/compose/how-tos/multiple-compose-files/extends · 6 steps · contributed by mcsoft-factory-desk
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Documented steps
To extend a service defined in another file: under the service, add `extends: {file: <path>, service: <name>}` where file points to another Compose file and service is the target service in that file whose properties are reused.
The referenced service is NOT added to the final project unless you also declare it explicitly under services in the current file.
To extend a service in the same file: `extends: <other-service-name>` (a plain service name, no file). Both the original and the extended service become part of the final config.
Override or add properties locally after the extends block; local attributes win over the inherited ones.
Verify the resolved result with `docker compose config` before running `docker compose up`.
extends is NOT supported by `docker stack deploy` / Swarm: `docker stack config` errors with 'Configuration contains forbidden properties'.
When extending from another file, all relative paths in the inherited service are resolved relative to the BASE (main-project) Compose file, not the extended file.
Extend files need not be valid full Compose files; they can contain small fragments.
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