docs: docker secrets support. (#12141)

Closes #12132

CHANGELOG.md

@@ -30,6 +30,7 @@
 * **Singlestat**: Fix singlestat threshold tooltip [#11971](https://github.com/grafana/grafana/issues/11971)
 * **Dashboard**: Hide grid controls in fullscreen/low-activity views [#11771](https://github.com/grafana/grafana/issues/11771)
 * **Dashboard**: Validate uid when importing dashboards [#11515](https://github.com/grafana/grafana/issues/11515)
+* **Docker**: Support for env variables ending with _FILE [grafana-docker #166](https://github.com/grafana/grafana-docker/pull/166), thx [@efrecon](https://github.com/efrecon) 
 
 # 5.1.3 (2018-05-16)
 

docs/sources/installation/docker.md

@@ -130,6 +130,18 @@ ID=$(id -u) # saves your user id in the ID variable
 docker run -d --user $ID --volume "$PWD/data:/var/lib/grafana" -p 3000:3000 grafana/grafana:5.1.0
 ```
 
+## Reading secrets from files (support for Docker Secrets)
+
+It's possible to supply Grafana with configuration through files. This works well with [Docker Secrets](https://docs.docker.com/engine/swarm/secrets/) as the secrets by default gets mapped into `/run/secrets/<name of secret>` of the container.
+
+You can do this with any of the configuration options in conf/grafana.ini by setting `GF_<SectionName>_<KeyName>_FILE` to the path of the file holding the secret.
+
+Let's say you want to set the admin password this way.
+
+- Admin password secret: `/run/secrets/admin_password`
+- Environment variable: `GF_SECURITY_ADMIN_PASSWORD_FILE=/run/secrets/admin_password`
+
+
 ## Migration from a previous version of the docker container to 5.1 or later
 
 The docker container for Grafana has seen a major rewrite for 5.1.