#dockerfile-lint

A rule based 'linter' for Dockerfiles. The linter rules can be used to check file syntax as well as arbitrary semantic and best practice attributes determined by the rule file writer.

#Rule Files Rule files are written in yaml. See the example rule file sample_rules.yaml in the root folder of the project. The rules are implememented using regular expressions, run on one instruction of the dockerfile at a time. The rule file has 4 sections, a profile section, a general section, a line rule section and a required instruction section.

##Profile Section The profile section gives information about the rule file The information here is meant to help a user select a rule file that is appropriate for a given dockerfile. Example:

profile:
  name: "Default"
  description: "Default Profile. Checks basic syntax."

##General Section This section contains general syntax rules.

##Rule Attributes

Here is an example of a line rule expressed in yaml:

    label: "is_latest_tag"
    regex: /latest/
    level: "info"
    inverse_rule: true
    message: "base image uses 'latest' tag"
    description: "using the 'latest' tag may cause unpredictable builds. It is recommended that a specific tag is used in the FROM line."
    reference_url: 

##Line Rule Section This section contains rules that must be run on a given instruction in the dockerfile. There is a rule to check the syntax of each instruction and zero or more rules for semantic checks. The example below shows rules to run against the 'FROM' instruction:

line_rules: 
    FROM: 
      paramSyntaxRegex: /.+/
      rules: 
        - 
          label: "is_latest_tag"
          regex: /latest/
          level: "info"
          message: "base image uses 'latest' tag"
          description: "using the 'latest' tag may cause unpredictable builds. It is recommended that a specific tag is used in the FROM line."
          reference_url: 
            - "https://docs.docker.com/reference/builder/"
            - "#from"
        - 
          label: "no_tag"
          regex: /[:]/
          level: "warn"
          inverse_rule: true
          message: "No tag is used"
          description: "No tag is used"
          reference_url: 
            - "https://docs.docker.com/reference/builder/"
            - "#from"
        - 
          label: "from_not_redhat"
          regex: /rhel|redhat*/
          inverse_rule: true
          level: "error"
          message: "Base Image is not from Red Hat"
          description: "Base Image must be from Red Hat"
          reference_url: 

Note the (optional) 'inverse_rule' attribute - this is just a convinient way to negate a regex rule - by default a rule is considered violated if it matches the regex pattern, but when 'inverse_rule' is set to 'true' the rule is violated if the line does not match the regex.

##Required Instruction Section This section includes a list of instructions that must exist in the dockerfile in order for it to be considered valid.

#Library Usage

##Node.js application use

Install from github from your application root directory:

npm install git+https://github.com/redhataccess/dockerfile_lint

Import and use the validator:

var fs = require('fs');
var rulefile = fs.readFileSync('/path/to/rulefile', 'utf8');
var DockerFileValidator = require('dockerfile_lint');
var validator = new DockeFileValidator(rulefile);
var result = validator.validate(dockerfile);

You can install the linter globally on your pc:

sudo npm install git+https://github.com/redhataccess/dockerfile_lint

Run the tool:

dockerfile_lint  -f /path/to/dockerfile  [-r /path/to/rule/file]

A default rule file is used if no rule file is given.

You can also run the tool without installing it - just clone the source repository and run the tool from the bin directory :

git clone [email protected]:redhataccess/dockerfile_lint.git
cd dockerfile_lint/bin
chmod 555 dockerfile_lint
dockerfile_lint  -f /path/to/dockerfile  [ -r /path/to/rule/file]

To display results as JSON use the '-j' option:

dockerfile_lint  -j -f /path/to/dockerfile  [ -r /path/to/rule/file]

Command Help:

dockerfile_lint  -h

#Credits The linter is based on https://github.com/Runnable/validate-dockerfile and https://github.com/goern/dockerfile_checker

MIT