require-quotes-in-ports-rule.md

Require Quotes in Ports Rule

Ensures that the port values in the ports section of services in the Docker Compose file are enclosed in quotes. Using quotes around port numbers can prevent YAML parsing issues and ensure that the ports are interpreted correctly.

This rule is fixable. The linter can automatically add the required quotes around port numbers without altering the ports themselves. The type of quotes (single or double) can be configured via the quoteType option.

• Rule Name: require-quotes-in-ports
• Type: warning
• Category: best-practice
• Severity: minor
• Fixable: true

Problematic code example

services:
  foo:
    image: image
    ports:
      - 80:80
      - 443:443

Correct code example (Single Quotes)

services:
  foo:
    image: image
    ports:
      - '80:80'
      - '443:443'

Correct code example (Double Quotes)

services:
  foo:
    image: image
    ports:
      - "80:80"
      - "443:443"

Rule Details and Rationale

This rule ensures that the port numbers specified in the ports section of services are enclosed in quotes. Quoting ports helps avoid potential issues with YAML parsing, where unquoted numbers might be misinterpreted or cause unexpected behavior. By enforcing this rule, we ensure that the configuration is more robust and consistent.

When mapping ports in the HOST:CONTAINER format, you may experience erroneous results when using a container port lower than 60, because YAML parses numbers in the format xx:yy as a base-60 value. For this reason, we recommend always explicitly specifying your port mappings as strings.

Options

The rule takes one string option, quoteType, to specify the type of quotes around port mappings:

• single
• double

By default, the rule enforces the use of single quotes.

Example

If you want to enforce the use of double quotes around port mappings you can do it like this:

{
  "rules": {
    "require-quotes-in-ports": [
      1,
      {
        "quoteType": "double"
      }
    ]
  }
}

Version

This rule was introduced in Docker-Compose-Linter 1.0.0.

References

• Stackoverflow Discussion: Quotes on docker-compose.yml ports
• Compose file reference
• Awesome Compose Examples