Being a Docker-based tool itself, Buddy provides everything you need to build, test, and orchestrate Docker images:

Docker action rosterDocker action roster

One of these actions is Dockerfile Linter, a handy tool that lets you check the Dockerfile syntax before building the image. The tool follows the best practices from the official Docker website so that you can be sure your images are optimized for maximum performance.

With this week's release the action has received support for environment variables, a nifty feature that will help you better organize your Docker workflows.

Example use case

You can use ENV VARs to store the path to the Dockerfile. First, you need to add the path to the variable in the Variables tab:

ENV VAR setupENV VAR setup

The you simply enter the variable name in the Linter's Dockerfile input path:

Docker linter configurationDocker linter configuration

The tool is very thorough and will always return all types of errors – even directives. If you wish, you can leave out specific error types in the Ignore tab of the action details.

Placing the action before the build and adding a conditional notification will keep you on toes in case Buddy detects errors with the Dockerfile:

Example Docker delivery pipelineExample Docker delivery pipeline

The linter is as an open-source project and as such can be used with any CI/CD tool.

Rules table

RulesDescription
EL0001Invalid line
ED0001All parser directives must be at the very top of a Dockerfile.
ED0002Directive appears more then once.
ED0003Directives should be lowercase.
ED0004Parser directive will be treated as a comment.
ED0005Missing value for directive.
ER0001Set the SHELL option -o (-eo for Alpine image) pipefail before RUN with a pipe in.
EU0001Last user should not be root.
EI0001There can only be one instruction like (CMD, HEALTHCHECK, ENTRYPOINT).
EI0002FROM may only be preceded by one or more ARG.
EF0001Missing FROM.
EC0001COPY --from cannot reference its own FROM alias.
EC0002COPY --from should reference a previously defined FROM alias.
EI0003MAINTAINER is deprecated, instead use LABEL.
EJ0001You must use double-quotes (") in JSON array.
EJ0002CMD and ENTRYPOINT should be written in JSON form.
EJ0003SHELL must be written in JSON form.
EF0002FROM aliases must be unique.
EF0003Using latest is prone to errors if the image will ever update.
EF0004Always tag the version of an image explicitly.
ER0002Delete the apt-get lists after installing something.
ER0003Use WORKDIR to switch to a directory.
ER0004Do not use sudo, consider using gosu.
ER0005Command (ssh, vim, shutdown, service, ps, free, top, kill, mount, ifconfig) does not make sense in a container.
ER0006Using (apt-get upgrade, dist-upgrade, apk upgrade, apt install) is not recommended.
EA0001Use curl or wget instead, and delete files when no longer needed.
EC0003Use ADD for extracting archives into a image.
ER0007Either use wget or curl, but not both.
ER0008Use SHELL to change the default shell.
ER0009Use the -y switch.
ER0010Avoid additional packages by specifying --no-install-recommends.
EA0002Use COPY instead of ADD for files and folders.
EC0004COPY with more then 2 arguments requires the last argument to end with /.
ER0011Use the --no-cache switch.
ER0012Pin versions in apt get install.
ER0013Pin versions in pip install.
ER0014Pin versions in npm install.
ER0015Pin versions in apk add.
ER0016Pin versions in gem install.
EI0004Don't use (ONBUILD,FROM,MAINTAINTER) in ONBUILD.
EW0001Use absolute WORKDIR.
EE0001Valid UNIX ports range from 0 to 65535.
EI0005Instructions should be uppercase.