Complete Guide to Deploying Phoenix Applications using Dokku 0.4.0

September 25, 2015

3 min read

This is a complete guide on how to deploy a phoenix application to a VPS using Dokku 0.4.0. Dokku is built on docker and allows you to deploy apps using a heroku like workflow.


You are deploying to a fresh VM running Ubuntu 14.04 x64 Your VPS has at least 1GB of system memory (workaround for 512MB machines)

Step 1: Installing dokku

The commands in this section are run on the VPS

First step is to SSH into your VPS and then install dokku.

On your VPS run:

$ apt-get update
$ wget
$ sudo DOKKU_TAG=v0.4.0 bash

Once it finishes, install the postgres plugin:

$ dokku plugin:install postgres

Step 2: Preparing your phoenix app

The changes in this section are done on your local machine

Now we need to make some changes to the application to get it production ready. First, lets commit prod.secret.exs to the git repo by commenting out the following line on the .gitignore file.


Next, open up the prod.secret.exs file and replace the secret key base with:

secret_key_base: System.get_env("SECRET_KEY_BASE")

Next replace the username, password and database lines with:

url: System.get_env("DATABASE_URL")

Your prod.secret.exs file should now look like this:

use Mix.Config

# In this file, we keep production configuration that
# you likely want to automate and keep it away from
# your version control system.
config :phoenix_dokku_example, PhoenixDokkuExample.Endpoint,
  secret_key_base: System.get_env("SECRET_KEY_BASE")

# Configure your database
config :phoenix_dokku_example, PhoenixDokkuExample.Repo,
  adapter: Ecto.Adapters.Postgres,
  url: System.get_env("DATABASE_URL"),
  pool_size: 20

Note: :phoenix_dokku_example and PhoenixDokkuExample would be replaced with your app name

Next, open up the prod.exs file and replace with your domain name.

Now we need to tell dokku how to build the app. To do so, create a new file in the root of the phoenix application and name it .buildpacks. Inside this file, copy and paste the following lines:

Step 3: Deploying your APP using GIT

The commands in this section are run on your local machine

Dokku uses git hooks to deploy, so we need to go ahead and add your VPS as a git remote:

$ git remote add dokku

Note: change and APP_NAME to your domain name. Make sure both are the same, for example if you wanted to deploy to the line above would look like this:

$ git remote add dokku [email protected]

Now we need to create a user called dokku on the VPS:

$ cat ~/.ssh/ | ssh [sudouser]@[yourdomain].com "sudo sshcommand acl-add dokku [description]"

Note: replace ~/.ssh/ with the location to the public key you are using, and [sudouser]@[yourdomain].com with your root user and domain name respectively.

Finally you can deploy your application to your VPS:

$ git push dokku master

Step 4: Configure hostname and virtual host

The commands in this section are run on the VPS

Next we need to make sure that the VHOST and HOSTNAME are properly set up, to do so ssh back into your VPS and run the following commands:

$ echo "" > /home/dokku/HOSTNAME
$ echo "" > /home/dokku/VHOST
$ dokku config:unset APP_NAME NO_VHOST
$ dokku domains APP_NAME

NOTE: and APP_NAME must be the same, and to be clear it doesn’t have to be a .com it can be any fully qualified domain name (FQDN) (.io, .org, .net etc…)

For example:

$ echo "" > /home/dokku/HOSTNAME
$ echo "" > /home/dokku/VHOST
$ dokku config:unset NO_VHOST
$ dokku domains

Step 5: Configure database and environment variables

The commands in this section are run on the VPS

Now we need to set up some environment variables:

$ dokku config:set APP_NAME MIX_ENV=prod
$ dokku config:set APP_NAME PORT=5000

Next, create and link the postgres database with the app and run the migrations. Replace DB_NAME with whatever name you want to give the database:

$ dokku postgres:create DB_NAME
$ dokku postgres:link DB_NAME APP_NAME
$ dokku run APP_NAME mix ecto.migrate

Now lets generate our application’s secret key

$ dokku run APP_NAME mix phoenix.gen.secret

This will print a string to your terminal window, this is your secret key, set it as an environment variable.

$ dokku config:set APP_NAME SECRET_KEY_BASE=your_secret_key

Go to your website and your phoenix app should be up and running. Congrats!

Whenever you want to update your app all you have to do is commit the changes and push it your sever from your local machine by running:

$ git push dokku master

Useful Dokku Commands

You can also run dokku commands directly from your local machine. For example if you want to run a migration:

$ ssh run APP_NAME mix ecto.migrate

You can set environment variables the same way:

 $ ssh config:set APP_NAME FOO=bar