support scripts.dokku in app.json. closes #1824

docs/deployment/deployment-tasks.md

@@ -0,0 +1,55 @@
+# Deployment Tasks
+
+Sometimes you need to run a command on at deployment time, but before an app is completely deployed.
+Common use cases include:
+
+* Checking a database is initialised
+* Running database migrations
+* Any commands required to set up the server (e.g. something like a Django `collectstatic`)
+
+## `app.json` and `scripts.dokku`
+
+Dokku accomplishes this by using an `app.json` file. We (mostly) use the same format as Heroku's [app.json](https://devcenter.heroku.com/articles/app-json-schema).
+However, dokku currently only supports the nodes `scripts.dokku.predeploy` and `scripts.dokku.postdeploy`.
+Simply place an `app.json` file in the root of your repository.
+NOTE: `app.json` is only supported in buildpack-deployed apps and postdeploy changes are not committed to the app image.
+
+### Example app.json
+
+```
+{
+  "name": "barebones nodejs",
+  "description": "A barebones Node.js app using Express 4.",
+  "keywords": [
+    "nodejs",
+    "express"
+  ],
+  "repository": "https://github.com/michaelshobbs/node-js-sample",
+  "scripts": {
+    "dokku": {
+      "predeploy": "touch /app/predeploy.test",
+      "postdeploy": "touch /app/postdeploy.test"
+    }
+  },
+  "env": {
+    "SECRET_TOKEN": {
+      "description": "A secret key for verifying the integrity of signed cookies.",
+      "value": "secret"
+    },
+    "WEB_CONCURRENCY": {
+      "description": "The number of processes to run.",
+      "generator": "echo 5"
+    }
+  },
+  "image": "gliderlabs/herokuish",
+  "addons": [
+    "dokku-postgres",
+    "dokku-redis"
+  ],
+  "buildpacks": [
+    {
+      "url": "https://github.com/heroku/heroku-buildpack-nodejs"
+    }
+  ]
+}
+```