How to fix ERROR: Service 'web' has an invalid healthcheck definition in Docker

# Docker Compose V2
docker compose config

# Docker Compose V1 (legacy)
docker-compose config

# WRONG - disable cannot be combined with other options
services:
  web:
    image: nginx
    healthcheck:
      disable: true
      test: ["CMD", "curl", "-f", "http://localhost/"]
      interval: 30s

# CORRECT - disable alone
services:
  web:
    image: nginx
    healthcheck:
      disable: true

# ALTERNATIVE - use test: ["NONE"] instead of disable
services:
  web:
    image: nginx
    healthcheck:
      test: ["NONE"]

services:
  web:
    image: nginx
    healthcheck:
      # Option 1: String format (runs via /bin/sh -c)
      test: curl -f http://localhost/ || exit 1

      # Option 2: CMD-SHELL array (explicit shell execution)
      test: ["CMD-SHELL", "curl -f http://localhost/ || exit 1"]

      # Option 3: CMD array (direct execution, no shell)
      test: ["CMD", "curl", "-f", "http://localhost/"]

      # Option 4: Disable healthcheck
      test: ["NONE"]

# WRONG - Array without CMD or CMD-SHELL prefix
test: ["curl", "-f", "http://localhost/"]

# WRONG - CMD as a string in the command
test: "CMD curl -f http://localhost/"

# WRONG - Missing failure handling in shell format
test: ["CMD-SHELL", "curl http://localhost/"]  # Should have || exit 1

# CORRECT
test: ["CMD", "curl", "-f", "http://localhost/"]

services:
  db:
    image: postgres:16
    healthcheck:
      test: ["CMD-SHELL", "pg_isready -U postgres"]
      # Valid duration formats
      interval: 30s       # 30 seconds
      timeout: 10s        # 10 seconds
      retries: 3          # integer, not a duration
      start_period: 1m30s # 1 minute 30 seconds
      start_interval: 5s  # 5 seconds (Docker 25.0+)

# WRONG - Missing unit
interval: 30

# WRONG - Invalid unit
timeout: 10sec

# WRONG - Quoted numbers
retries: "3"

# CORRECT
interval: 30s
timeout: 10s
retries: 3

# For Docker Compose V1 (legacy)
version: "2.1"  # Minimum for healthcheck
# or
version: "3"    # Also supports healthcheck

services:
  web:
    image: nginx
    healthcheck:
      test: ["CMD", "curl", "-f", "http://localhost/"]

# Docker Compose V2 - version is optional
services:
  web:
    image: nginx
    healthcheck:
      test: ["CMD", "curl", "-f", "http://localhost/"]

# Docker Compose V2
docker compose version

# Docker Compose V1 (legacy)
docker-compose version

# WRONG - $? causes interpolation error
services:
  web:
    healthcheck:
      test: ["CMD-SHELL", "curl -f http://localhost/ && echo $?"]

# CORRECT - Escape the dollar sign
services:
  web:
    healthcheck:
      test: ["CMD-SHELL", "curl -f http://localhost/ && echo $$?"]

# BETTER - Use explicit exit
services:
  web:
    healthcheck:
      test: ["CMD-SHELL", "curl -f http://localhost/ || exit 1"]

services:
  db:
    image: postgres:16
    environment:
      POSTGRES_USER: myuser
    healthcheck:
      # Use shell variable syntax carefully
      test: ["CMD-SHELL", "pg_isready -U $${POSTGRES_USER}"]
      # Or use the direct value
      test: ["CMD-SHELL", "pg_isready -U myuser"]

# WRONG - Inconsistent indentation
services:
  web:
    image: nginx
    healthcheck:
      test: ["CMD", "curl", "-f", "http://localhost/"]
    interval: 30s  # This is at wrong level - not part of healthcheck!

# CORRECT - All options indented under healthcheck
services:
  web:
    image: nginx
    healthcheck:
      test: ["CMD", "curl", "-f", "http://localhost/"]
      interval: 30s
      timeout: 10s
      retries: 3
      start_period: 40s

# Using yamllint
yamllint docker-compose.yml

# Or validate with docker compose
docker compose config --quiet && echo "Valid" || echo "Invalid"