godolint

A Dockerfile linter that helps you build best practice Docker images (inspired by Haskell Dockerfile Linter). This tool performs docker rule checks based on an abstract syntax tree (AST) of a Dockerfile where the AST is generated using moby/buildkit parser.

Dependency

• moby/buildkit/frontend/dockerfile/parser: The official Dockerfile parser provided by moby. Used when parsing Dockerfile.

Usage

You can run godolint locally to lint your Dockerfile.

$ godolint <Dockerfile>

godolint prints out any violation of the best practices it finds to the standard output, and exit with a non-zero exit status.

Example

Here are examples of the outputs when godolint lints Dockerfiles that have some violations.

$ godolint testdata/DL3000_Dockerfile
#3 DL3000 Use absolute WORKDIR.

$ godolint testdata/DL3001_Dockerfile
#6 DL3001 For some bash commands it makes no sense running them in a Docker container like `ssh`, `vim`, `shutdown`, `service`, `ps`, `free`, `top`, `kill`, `mount`, `ifconfig`.

Options

The available options are:

  --ignore RULECODE     A rule to ignore. If present, the ignore list in the
                        config file is ignored

  --help        -h      Print this help message and exit.
  --version     -v      Print the version information

Ignore violations

You can ignore specific violation using the --ignore option by specifying the rule to ignore. For the list of rules, see Rules. For example, here is an example to ignore the rule DL3000:

$ godolint --ignore DL3000 testdata/DL3000_Dockerfile

Installation

You can download a binary from the release page and place it in $PATH directory.

Or you can use go get:

$ go get github.com/zabio3/godolint

Rules

The following is a list of the implemented rules. Dockerfile lint rule provided by hadolint

Rule	Description
DL3000	Use absolute WORKDIR.
DL3001	For some bash commands it makes no sense running them in a Docker container like ssh, vim, shutdown, service, ps, free, top, kill, mount, ifconfig.
DL3002	Last user should not be root.
DL3003	Use WORKDIR to switch to a directory.
DL3004	Do not use sudo as it leads to unpredictable behavior. Use a tool like gosu to enforce root.
DL3005	Do not use apt-get upgrade or dist-upgrade.
DL3007	Using latest is prone to errors if the image will ever update. Pin the version explicitly to a release tag.
DL3006	Always tag the version of an image explicitly.
DL3008	Pin versions in apt-get install.
DL3009	Delete the apt-get lists after installing something.
DL3010	Use ADD for extracting archives into an image.
DL3011	Valid UNIX ports range from 0 to 65535.
DL3012	Provide an email address or URL as maintainer. (This rule is DEPRECATED and no longer active)
DL3013	Pin versions in pip.
DL3014	Use the -y switch.
DL3015	Avoid additional packages by specifying --no-install-recommends.
DL3016	Pin versions in npm.
DL3017	Do not use apk upgrade.
DL3018	Pin versions in apk add. Instead of apk add <package> use apk add <package>=<version>.
DL3019	Use the --no-cache switch to avoid the need to use --update and remove /var/cache/apk/* when done installing packages.
DL3020	Use COPY instead of ADD for files and folders.
DL3021	COPY with more than 2 arguments requires the last argument to end with /.
DL3022	COPY --from should reference a previously defined FROM alias.
DL3023	COPY --from cannot reference its own FROM alias.
DL3024	FROM aliases (stage names) must be unique.
DL3025	Use arguments JSON notation for CMD and ENTRYPOINT arguments.
DL4000	MAINTAINER is deprecated.
DL4001	Either use Wget or Curl but not both.
DL4003	Multiple CMD instructions found.
DL4004	Multiple ENTRYPOINT instructions found.
DL4005	Use SHELL to change the default shell.
DL4006	Set the SHELL option -o pipefail before RUN with a pipe in it.

AST

Dockerfile syntax is fully described in the Dockerfile reference. For the definitions of the AST, see moby/buildkit.

Contribution

Contributions are of course always welcome!

1. Fork zabio3/godolint (https://github.com/zabio3/godolint/fork)
2. Run go get to install dependencies
3. Create a feature branch
4. Commit your changes
5. Run test using go test ./...
6. Create a Pull Request

See CONTRIBUTING.md for details.

Build Docker Image

1. Run make docker
2. Create a new tag for that release (in this example 0.1.2): docker tag zabio3/godolint zabio3/godolint:v0.1.2
3. Push to Docker hub: docker push zabio3/godolint zabio3/godolint:v0.1.2