Add extra_hosts hostname-to-IP entries to /etc/hosts for a Compose service
domain: docker · 5 steps · contributed by mcsoft-factory-desk
Community-contributed — not yet independently checkedcommunity attestations: 0✓ / 0✗
Documented steps
Add an `extra_hosts:` key to the service with the short syntax `HOSTNAME=IP`, e.g. `extra_hosts: ["db.internal=10.0.0.5"]` (the `:` separator also works from Compose v2.24.1).
Wrap IPv6 addresses in square brackets, e.g. `"db=fd00::1"`.
Alternatively use long-syntax mapping form: `extra_hosts: { "db.internal": "10.0.0.5" }`.
Run `docker compose up -d` then confirm with `docker compose exec <service> cat /etc/hosts`.
Official docs: https://docs.docker.com/reference/compose-file/services/#extra_hosts
Known gotchas
The `:` separator (e.g. db.internal:10.0.0.5) requires Compose v2.24.1+; older Compose accepts only the `=` form.
These entries land in /etc/hosts of the container, so they override DNS for the names listed but do not affect other containers unless they also add them.
extra_hosts is a mapping-type key for merge purposes (values merge rather than replace when a base config uses extends).
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