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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.

Dockerfile support is considered a power user feature. By using Dockerfile-based deployment, you agree that you will not have the same comfort as that enjoyed by buildpack users, and Dokku features may work differently. Differences between the two systems will be documented here.

Usage

Detection

This builder will be auto-detected in the following case:

  • A Dockerfile exists in the root of the app repository.

Dokku will only select the dockerfile builder if both the herokuish and pack builders are not detected and a Dockerfile exists. For more information on how those are detected, see the following links:

Switching from buildpack deployments

If an application was previously deployed via buildpacks, the following commands should be run before a Dockerfile deploy will succeed:

dokku config:unset --no-restart node-js-app DOKKU_PROXY_PORT_MAP 

Changing the Dockerfile location

The previous method to perform this - via docker-options:add - should be removed in favor of the builder-dockerfile:set command outlined here.

When deploying a monorepo, it may be desirable to specify the specific path of the Dockerfile file to use for a given app. This can be done via the builder-dockerfile:set command. If a value is specified and that file does not exist in the app's build directory, then the build will fail.

dokku builder-dockerfile:set node-js-app dockerfile-path Dockerfile2

The default value may be set by passing an empty value for the option:

dokku builder-dockerfile:set node-js-app dockerfile-path

The dockerfile-path property can also be set globally. The global default is Dockerfile, and the global value is used when no app-specific value is set.

dokku builder-dockerfile:set --global dockerfile-path Dockerfile2

The default value may be set by passing an empty value for the option.

dokku builder-dockerfile:set --global dockerfile-path

Displaying builder-dockerfile reports for an app

New as of 0.25.0

You can get a report about the app's storage status using the builder-dockerfile:report command:

dokku app-json:report
=====> node-js-app builder-dockerfile information
       Builder-dockerfile computed dockerfile path: Dockerfile2
       Builder-dockerfile global dockerfile path:   Dockerfile
       Builder-dockerfile dockerfile path:          Dockerfile2
=====> python-sample builder-dockerfile information
       Builder-dockerfile computed dockerfile path: Dockerfile
       Builder-dockerfile global dockerfile path:   Dockerfile
       Builder-dockerfile dockerfile path:
=====> ruby-sample builder-dockerfile information
       Builder-dockerfile computed dockerfile path: Dockerfile
       Builder-dockerfile global dockerfile path:   Dockerfile
       Builder-dockerfile dockerfile path:

You can run the command for a specific app also.

dokku builder-dockerfile:report node-js-app
=====> node-js-app builder-dockerfile information
       Builder-dockerfile computed dockerfile path: Dockerfile2
       Builder-dockerfile global dockerfile path:   Dockerfile
       Builder-dockerfile dockerfile path:          Dockerfile2

You can pass flags which will output only the value of the specific information you want. For example:

dokku builder-dockerfile:report node-js-app --builder-dockerfile-dockerfile-path
Dockerfile2

Build-time configuration variables

For security reasons - and as per Docker recommendations - Dockerfile-based deploys have variables available only during runtime.

For users that require customization in the build phase, you may use build arguments via the docker-options plugin:

dokku docker-options:add node-js-app build '--build-arg NODE_ENV=production'

Once set, the Dockerfile usage would be as follows:

FROM ubuntu:18.04

# set the argument default
ARG NODE_ENV=production

# use the argument
RUN echo $NODE_ENV

You may also set the argument as an environment variable

FROM ubuntu:18.04

# set the argument default
ARG NODE_ENV=production

# assign it to an environment variable
# we can wrap the variable in brackets
ENV NODE_ENV ${NODE_ENV}

# or omit them completely

# use the argument
RUN echo $NODE_ENV

Building images with Docker Buildkit

If your Dockerfile is using Docker engine's buildkit (not to be confused with buildpacks), then the DOCKER_BUILDKIT=1 environment variable needs to be set. Additionally, complete build log output can be forced via BUILDKIT_PROGRESS=plain. Both of these environment variables can be set as follows:

# via config:set
dokku config:set --global DOCKER_BUILDKIT=1 BUILDKIT_PROGRESS=plain

# on the /etc/default/dokku file
echo DOCKER_BUILDKIT=1 | sudo tee -a /etc/default/dokku
echo BUILDKIT_PROGRESS=plain | sudo tee -a /etc/default/dokku

Buildkit directory caching

Buildkit implements the RUN --mount option, enabling mount directory caches for RUN directives. The following is an example that mounts debian packaging related directories, which can speed up fetching of remote package data.

FROM debian:latest
RUN --mount=target=/var/lib/apt/lists,type=cache \
    --mount=target=/var/cache/apt,type=cache \
    apt-get update \
 && DEBIAN_FRONTEND=noninteractive apt-get install -y --no-install-recommends \
      git

Mount cache targets may vary depending on the tool in use, and users are encouraged to investigate the directories that apply for their language and framework.

You would adjust the cache directory for whatever application cache you have, e.g. /root/.pnpm-store/v3 for pnpm, $HOME/.m2 for maven, or /root/.cache for golang.

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 Node.js image, with the following ENTRYPOINT:

ENTRYPOINT ["node"]

You can do:

dokku config:set node-js-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 ubuntu:18.04
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.

Exposed ports

See the port management documentation for more information on how Dokku exposes ports for applications and how you can configure these for your app.

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