Merge pull request exercism#3591 from nilbus/docker-default-port

Provide a default port, making .env optional

docker-compose.yml

@@ -9,7 +9,7 @@ services:
       - db
     command: rerun -b --ignore='{**/*.{scss,css,js,coffee,erb},test/**}' 'puma -p 4567'
     ports:
-      - "${EXTERNAL_PORT}:4567"
+      - "${EXTERNAL_PORT-4567}:4567"
     environment:
       # These will ensure that certain development commands which
       # use 'psql' will also include our custom database config.

docker/README.md

@@ -61,21 +61,11 @@ welcome to give it a shot!
 
 ## Setting up exercism.io
 
-First, create an `.env` file in the root of your repository with
-the following in it:
+First, create an empty `.env` file in the root of your repository. This file
+may be used to pass environment variables to the application, as documented
+below. It may be empty but [must exist][required-env-file].
 
-```
-EXTERNAL_PORT=4567
-```
-
-You may also want to set up GitHub OAuth as per the instructions in
-[`CONTRIBUTING.md`][], in which case you can add your GitHub OAuth
-credentials, too:
-
-```
-EXERCISM_GITHUB_CLIENT_ID=your_github_oauth_client_id
-EXERCISM_GITHUB_CLIENT_SECRET=your_github_oauth_client_secret
-```
+[required-env-file]: https://github.com/docker/compose/issues/3560
 
 Then run:
 
@@ -90,8 +80,8 @@ Now your database is set up. To get the site up and running, run:
 
     docker-compose up
 
-If you're on Linux, your development instance of exercism.io will be running
-at http://localhost:4567.
+If you're Docker for Mac, or Docker for Windows, or native Linux, your
+development instance of exercism.io will be running at http://localhost:4567.
 
 Otherwise, if you're on a system using Docker Toolbox, your development
 server will actually be running on your Docker Machine VM, *not* on
@@ -104,6 +94,18 @@ Suppose this command tells you that your Docker Machine VM is at
 192.168.99.100. Then your development instance of exercism.io will be at
 http://192.168.99.100:4567.
 
+## Setting up OAuth
+
+In development mode, the application presents an _Assume_ menu in the
+upper-right-hand corner, allowing you to assume the role of one of several
+preset users.
+
+You may also set up GitHub OAuth as per the instructions in
+[`CONTRIBUTING.md`][], in which case you can add your GitHub OAuth credentials:
+
+    EXERCISM_GITHUB_CLIENT_ID=your_github_oauth_client_id
+    EXERCISM_GITHUB_CLIENT_SECRET=your_github_oauth_client_secret
+
 ## Changing The Port
 
 By default, the app will be exposed at port 4567, but you can change this