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require-quotes-in-ports-rule.md

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Require Quotes in Ports Rule

Ensures that the port values in the ports and expose sections 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
    expose:
      - 3000

Correct Code Example

# Single Quotes
services:
  foo:
    image: image
    ports:
      - '80:80'
      - '443:443'
    expose:
      - '3000'
# Double Quotes
services:
  foo:
    image: image
    ports:
      - "80:80"
      - "443:443"
    expose:
      - "3000"

Rule Details and Rationale

This rule ensures that the port numbers specified in the ports and expose sections 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.

Although the expose section in Docker Compose does not suffer from the same YAML parsing vulnerabilities as the ports section, it is still recommended to enclose exposed ports in quotes. Consistently using quotes across both ports and expose sections creates a uniform configuration style, making the file easier to read and maintain.

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 v1.0.0.

Handling expose section is added in 2.0.0

References