New action: Dockerfile Linter
Hey there, Docker junkies! We know that you love you Docker, and you know that we love Docker, so why not help our blue friend stay fit & healthy together? For this, we have created a new action called Dockerfile Linter. The linter lets you verify Dockerfile syntax to make sure it follows the best practices for building efficient Docker images.
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Configuration is very simple and basically involves selecting the Dockerfile from the filesystem and the shell in which the instructions will be analyzed (sh, bash, dash, ksh):
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Ignore tab of the action details.
The linter should always come as the first action in Docker-building pipelines. We also recommend adding a conditional notification to let your team know in case something goes wrong:
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Rules table
| Rules | Description |
|---|---|
EL0001 | Invalid line |
ED0001 | All parser directives must be at the very top of a Dockerfile. |
ED0002 | Directive appears more then once. |
ED0003 | Directives should be lowercase. |
ED0004 | Parser directive will be treated as a comment. |
ED0005 | Missing value for directive. |
ER0001 | Set the SHELL option -o (-eo for Alpine image) pipefail before RUN with a pipe in. |
EU0001 | Last user should not be root. |
EI0001 | There can only be one instruction like (CMD, HEALTHCHECK, ENTRYPOINT). |
EI0002 | FROM may only be preceded by one or more ARG. |
EF0001 | Missing FROM. |
EC0001 | COPY --from cannot reference its own FROM alias. |
EC0002 | COPY --from should reference a previously defined FROM alias. |
EI0003 | MAINTAINER is deprecated, instead use LABEL. |
EJ0001 | You must use double-quotes (") in JSON array. |
EJ0002 | CMD and ENTRYPOINT should be written in JSON form. |
EJ0003 | SHELL must be written in JSON form. |
EF0002 | FROM aliases must be unique. |
EF0003 | Using latest is prone to errors if the image will ever update. |
EF0004 | Always tag the version of an image explicitly. |
ER0002 | Delete the apt-get lists after installing something. |
ER0003 | Use WORKDIR to switch to a directory. |
ER0004 | Do not use sudo, consider using gosu. |
ER0005 | Command (ssh, vim, shutdown, service, ps, free, top, kill, mount, ifconfig) does not make sense in a container. |
ER0006 | Using (apt-get upgrade, dist-upgrade, apk upgrade, apt install) is not recommended. |
EA0001 | Use curl or wget instead, and delete files when no longer needed. |
EC0003 | Use ADD for extracting archives into a image. |
ER0007 | Either use wget or curl, but not both. |
ER0008 | Use SHELL to change the default shell. |
ER0009 | Use the -y switch. |
ER0010 | Avoid additional packages by specifying --no-install-recommends. |
EA0002 | Use COPY instead of ADD for files and folders. |
EC0004 | COPY with more then 2 arguments requires the last argument to end with /. |
ER0011 | Use the --no-cache switch. |
ER0012 | Pin versions in apt get install. |
ER0013 | Pin versions in pip install. |
ER0014 | Pin versions in npm install. |
ER0015 | Pin versions in apk add. |
ER0016 | Pin versions in gem install. |
EI0004 | Don't use (ONBUILD,FROM,MAINTAINTER) in ONBUILD. |
EW0001 | Use absolute WORKDIR. |
EE0001 | Valid UNIX ports range from 0 to 65535. |
EI0005 | Instructions should be uppercase. |
Jarek Dylewski
Customer Support
A journalist and an SEO specialist trying to find himself in the unforgiving world of coders. Gamer, a non-fiction literature fan and obsessive carnivore. Jarek uses his talents to convert the programming lingo into a cohesive and approachable narration.