Merge pull request #19 from discordianfish/add-docker-install

Add Docker install instructions

content/docs/introduction/install.md

@@ -17,4 +17,58 @@ For building Prometheus from source, see the relevant [`README.md` section](http
 
 ## Using Docker
 
-TODO: Add docker instructions.
+All Prometheus services are available as Docker images under the
+[prom](https://registry.hub.docker.com/repos/prom/) organization.
+
+Running Prometheus on Docker is as simple as
+ `docker run -p 9090:9090 prom/prometheus`. This starts Prometheus with
+a sample configuration and exposes it on port 9090.
+
+The Prometheus image uses a volume to store the actual metrics. For
+production deployments it is highly recommended to use the
+[Data Volume Container](https://docs.docker.com/userguide/dockervolumes/#creating-and-mounting-a-data-volume-container)
+pattern to ease managing the data on Prometheus upgrades.
+
+To provide your own configuration, there are several options. Here are
+two examples.
+
+### Volumes & bind-mount
+
+Bind-mount your prometheus.conf from the host by running:
+
+```
+docker run -p 9090:9090 -v /tmp/prometheus.conf:/prometheus.conf \
+       prom/prometheus
+```
+
+Or use an additional volume for the config:
+
+```
+docker run -p 9090:9090 -v /prometheus-data \
+       prom/prometheus -config.file=/prometheus-data/prometheus.conf
+```
+
+### Custom image
+
+To avoid managing a file on the host and bind-mount it, the
+configuration can be baked into the image. This works well if the
+configuration itself is rather static and the same across all
+environments.
+
+For this, create a new directory with a Prometheus configuration and a
+Dockerfile like this:
+
+```
+FROM prom/prometheus
+ADD prometheus.conf /
+```
+
+Now build and run it:
+
+```
+docker build -t my-prometheus .
+docker run -p 9090:9090 my-prometheus
+```
+
+A more advanced option is to render the config dynamically on start
+with some tooling or even have a daemon update it periodically.