dokku/docs/deployment/dockerfiles.md

Dockerfile Deployment

New as of 0.3.15

While Dokku normally defaults to using heroku buildpacks for deployment, you can also use docker's native Dockerfile system to define a container.

To use a dockerfiles for deployment, commit a valid Dockerfile to the root of your repository and push the repository to your Dokku installation. If this file is detected, Dokku will default to using it to construct containers except in the following two cases:

• The application has a BUILDPACK_URL environment variable set via the dokku config:set command or in a committed .env file. In this case, Dokku will use your specified buildpack.
• The application has a .buildpacks file in the root of the repository. In this case, Dokku will use your specified buildpack(s).

Exposed ports

Dokku will extract all tcp ports exposed using the EXPOSE directive and use said ports with nginx to proxy your app to those ports. (nginx does not support proxying udp) If you would like to change the exposed port, you should do so within your Dockerfile and app.

NOTE: UDP ports can be exposed by disabling the nginx proxy with dokku proxy:disable myapp

If you do not have a port explicitly exposed, Dokku will automatically expose port 5000 for your application.

Customizing the run command

By default no arguments are passed to docker run when deploying the container and the CMD or ENTRYPOINT defined in the Dockerfile are executed. You can take advantage of docker ability of overriding the CMD or passing parameters to your ENTRYPOINT setting $DOKKU_DOCKERFILE_START_CMD. Let's say for example you are deploying a base nodejs image, with the following ENTRYPOINT:

ENTRYPOINT ["node"]

You can do:

dokku config:set APP DOKKU_DOCKERFILE_START_CMD="--harmony server.js"

To tell docker what to run.

Setting $DOKKU_DOCKERFILE_CACHE_BUILD to true or false will enable or disable docker's image layer cache. Lastly, for more granular build control, you may also pass any docker build option to docker, by setting $DOKKU_DOCKER_BUILD_OPTS.

Procfiles and Multiple Processes

New as of 0.5.0

You can also customize the run command using a Procfile, much like you would on Heroku or with a buildpack deployed app. The Procfile should contain one or more lines defining process types and associated commands. When you deploy your app a Docker image will be built, the Procfile will be extracted from the image (it must be in the folder defined in your Dockerfile as WORKDIR or /app) and the commands in it will be passed to docker run to start your process(es). Here's an example Procfile:

web: bin/run-prod.sh
worker: bin/run-worker.sh

And Dockerfile:

FROM debian:jessie
WORKDIR /app
COPY . ./
CMD ["bin/run-dev.sh"]

When you deploy this app the web process will automatically be scaled to 1 and your Docker container will be started basically using the command docker run bin/run-prod.sh. If you want to also run a worker container for this app, you can run dokku ps:scale worker=1 and a new container will be started by running docker run bin/run-worker.sh (the actual docker run commands are a bit more complex, but this is the basic idea). If you use an ENTRYPOINT in your Dockerfile, the lines in your Procfile will be passed as arguments to the ENTRYPOINT script instead of being executed.