Dockerfile Deployment¶
New
Introduced in 0.3.15
builder-dockerfile:report [<app>] [<flag>] # Displays a builder-dockerfile report for one or more apps
builder-dockerfile:set <app> <key> (<value>) # Set or clear a builder-dockerfile property for an app
While Dokku normally defaults to using Heroku buildpacks for deployment, you can also use Docker's native Dockerfile system to define a container.
Info
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
Dockerfileexists 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 and ports were customized, the following commands should be run prior to a deploy to ensure the Dockerfile ports are respected:
Changing the Dockerfile location¶
Info
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.
For git push, git:from-archive, and git:sync workflows, the Dockerfile is extracted directly from the source code, respecting the configured dockerfile-path property value.
The default value may be set by passing an empty value for the option:
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.
The default value may be set by passing an empty value for the option.
Displaying builder-dockerfile reports for an app¶
New
Introduced in 0.25.0
You can get a report about the app's storage status using the builder-dockerfile:report command:
=====> 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.
You can pass flags which will output only the value of the specific information you want. For example:
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. All environment variables set by the config plugin are automatically exported during a docker build, and thus --build-arg only requires setting a key without a value.
Once set, the Dockerfile usage would be as follows:
FROM ubuntu:20.04
# 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:20.04
# 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 (unless you're using Docker Engine v24 or higher, which uses BuildKit by default). Additionally, complete build log output can be forced via BUILDKIT_PROGRESS=plain. Both of these environment variables can be set as follows:
echo "export DOCKER_BUILDKIT=1" | sudo tee -a /etc/default/dokku
echo "export 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:
You can do:
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
Introduced in 0.5.0
See the Procfile documentation for more information on how to specify different processes for your app.
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.