Set up an stunnel endpoint for the engine.

blimp/docs/container.md

 # Running the engine in a Docker container
 
 For local development and testing, you can run the engine in a Docker
 container.
 
 The steps are:
 
 1. Bundle the engine and its dependencies.
 
 1. Build a Docker image.
@@ skipping 41 matching lines @@
 dependencies.
 
 ## Build Docker Image
 
 Using the tarfile you can create a Docker image:
 
 ```bash
 docker build -t blimp_engine - < ./out-linux/Debug/blimp_engine_bundle.tar
 ```
 
-## Create Docker Container
+## Running the Engine in a Docker Container
 
-From the Docker image you can create a Docker container (i.e. run the engine):
+After building the Docker image you can launch the engine inside the Docker
+container.
+
+### Setting up an Environment
+
+A little prep work is necessary to enable the engine to start as it requires a
+few files that are not provided by the container. You need:
+
+*   A directory (`$CONFIG_DIR`) with permissions of 0755 (ie. world accessable)
+*   `$CONFIG_DIR/stunnel.pem`: A PEM encoded file with a private key and a
+    public certificate. Permissions should be set to 644.
+*   `$CONFIG_DIR/client_token`: A file with a non-empty string used as the
+    client token (the shared secret between the client and the engine).
+    Persmissions should also be set to 644.
+
+This setup step is only required once and can be reused for all the rest of the
+runs of the engine.
+
+### Running the Engine
+
+Once the `$CONFIG_DIR` is set up, you can launch the engine in the Docker
+container:
 
 ```bash
-docker run blimp_engine
+docker run -v $CONFIG_DIR:/engine/data -p 443:25466 blimp_engine
 ```
-
 You can also pass additional flags:
 
 ```bash
-docker run blimp_engine --with-my-flags
+docker run ... blimp_engine --with-my-flags
 ```
-
 See the [blimp engine `Dockerfile`](../engine/Dockerfile) to find out what flags
 are passed by default.
 
-### Mapping Volumes into the Docker Container
-
-If you need to map a directory into the Docker container (eg. for necessary
-files):
-
-```bash
-docker run -v /path/to/srcdir:/path/to/docker/destdir blimp_engine
-```
-
-NB: The permissions of the directory and the files outside of the Docker
-container will be carried over into the container.