docker-compose-standards.mdc

---
description: Docker Compose standards Rule
globs: 
alwaysApply: false
---

## Rule Details

- **Name:** docker_compose_best_practices

- **Description:** Enforces best practices in docker-compose files to ensure maintainability, security, and consistency

## Filters
- file name: `docker-compose\\.ya?ml$`
- event: `(file_create|file_modify)`

## Rejections
- Conditions:
  - pattern `^\\s*version\\s*:` – The 'version' field is deprecated in Docker Compose files. Compose files are now version-less by default.

## Rejections
- Conditions:
  - pattern `^(  |\t)` – Inconsistent indentation detected. Use 2 spaces for indentation.

## Rejections
- Conditions:
  - pattern `^\\s*links\\s*:` – The 'links' key is deprecated. Use networks and service names for inter-service communication.

## Rejections
- Conditions:
  - pattern `^\\s*image\\s*:\\s*[^:]+$` – Specify an explicit image tag to ensure consistency.

## Rejections
- Conditions:
  - pattern `^\\s*privileged\\s*:\\s*true` – Running services in privileged mode is discouraged for security reasons.

## Rejections
- Conditions:
  - pattern `^\\s*services\\s*:\\s*[^\\n]+\\n(?!.*\\blimits\\b)` – Define resource limits for each service to prevent resource exhaustion.

## Suggestions
- Guidance:
To adhere to Docker Compose best practices:

1. **Omit the 'version' field**: Compose files are version-less by default.
   ```yaml
   services:
     web:
       image: nginx
   ```

2. **Use consistent indentation**: Use 2 spaces for indentation.
   ```yaml
   services:
     web:
       image: nginx
   ```

3. **Avoid 'links' key**: Use networks and service names for service communication.
   ```yaml
   services:
     web:
       image: nginx
       networks:
         - my-network
     db:
       image: mysql
       networks:
         - my-network
   networks:
     my-network:
   ```

4. **Specify explicit image tags**: Prevent unintended updates by defining image tags.
   ```yaml
   services:
     web:
       image: nginx:1.21.0
   ```

5. **Avoid privileged mode**: Do not use 'privileged: true'. Grant specific capabilities if necessary.
   ```yaml
   services:
     web:
       image: nginx
       cap_add:
         - NET_ADMIN
   ```

6. **Define resource limits**: Prevent services from consuming excessive resources.
   ```yaml
   services:
     web:
       image: nginx
       deploy:
         resources:
           limits:
             cpus: '0.50'
             memory: '512M'
   ```

Implementing these practices ensures secure, maintainable, and consistent Docker Compose configurations.

## Metadata
- Priority: high
- Version: 1.1