title: Is this the right way to run a `release` command for a Heroku Review app?
body: <p>I'm trying to configure a review app on Heroku. For every PR, I'd like to deploy and build the Dockerfile, then run my migrations command. </p>
  
  <p>With the below configs, the Dockerfile deploys fine, and the app appears to work as intended. </p>
  
  <p>Dockerfile: </p>
  
  <pre><code>FROM hasura/graphql-engine:v1.0.0-beta.4
  ENV HASURA_GRAPHQL_ENABLE_CONSOLE=true
  CMD graphql-engine \
      --database-url $DATABASE_URL \
      serve \
      --server-port $PORT
  </code></pre>
  
  <p>heroku.yml</p>
  
  <pre><code>build:
    docker:
      web: Dockerfile
  </code></pre>
  
  <p>app.json</p>
  
  <pre><code>{
    "name": "my_project",
    "formation": {
      "web": {
        "quantity": 1,
        "size": "free"
      }
    },
    "addons": [
      {
        "plan": "heroku-postgresql:hobby-dev",
        "options": { "version": "9.6" }
      }
    ],
    "scripts": {},
    "buildpacks": [],
    "stack": "container"
  }
  </code></pre>
  
  <p>But, when I add (what I think is) the release script for migrations, the build fails. </p>
  
  <p>heroku.yml with release script:</p>
  
  <pre><code>release:
    image: Dockerfile
    command:
      - cd ./migrations &amp;&amp; ./hasura migrate apply --endpoint $(heroku info -s | grep web_url | cut -d= -f2)
  </code></pre>
  
  <p>This results in the build error:</p>
  
  <pre><code>=== Fetching app code...
  =!= Couldn't find the release image configured for this app. Is there a matching run process?
  </code></pre>
  
  <p>I've also tried to add a <code>release</code> key to the <code>scripts</code> key in <code>app.json</code>, but this doesn't appear to do anything.</p>