Docker Errors Compose

docker-errors-compose

Quick Reference

First Response: Validate the Compose File

ALWAYS run docker compose config before debugging any Compose error. This command parses, resolves variables, and renders the final configuration. If it fails, the Compose file itself is broken.

# Validate and render resolved config
docker compose config

# Validate without output (exit code only)
docker compose config -q

# Show resolved environment variables
docker compose config --environment

Critical Warnings

NEVER ignore docker compose config validation errors — they indicate structural problems that ALWAYS cause runtime failures.

NEVER use depends_on without condition: service_healthy when the dependent service needs initialization time (databases, message brokers). The default service_started condition only waits for the container to start, NOT for the application to be ready.

NEVER use the deprecated version: field — it is ignored by Compose v2 and generates warnings.

ALWAYS use named volumes for persistent data. Anonymous volumes are lost on docker compose down.

ALWAYS quote port mappings that start with numbers below 60 to prevent YAML parsing as sexagesimal (base-60) numbers.

Diagnostic Decision Tree

Compose File Won't Parse

docker compose config fails
├── YAML syntax error?
│   ├── Check indentation (spaces only, NEVER tabs)
│   ├── Check colons have space after them in mappings
│   └── Check strings with special chars are quoted
├── "services" missing?
│   └── The `services` key is REQUIRED — add it
├── Unknown attribute error?
│   ├── Check spelling of Compose directives
│   └── Check indentation level (attribute under wrong parent)
└── Variable interpolation error?
    ├── Unset variable? → Use ${VAR:-default} or set in .env
    ├── Dollar sign in value? → Escape with $$ (e.g., $$HOME)
    └── Single-quoted in .env? → Values are literal, no interpolation

Services Won't Start

docker compose up fails
├── Port conflict?
│   ├── "port is already allocated" → Find process: lsof -i :PORT
│   └── Two services using same host port → Change one
├── Dependency failure?
│   ├── "dependency failed to start" → Check dependent service logs
│   ├── Healthcheck timeout → Increase interval/retries/start_period
│   └── service_completed_successfully never exits 0 → Fix init service
├── Build failure?
│   ├── "build path ... does not exist" → Check context path
│   ├── Dockerfile not found → Check dockerfile path relative to context
│   └── Build context too large → Add .dockerignore
├── Image not found?
│   ├── "pull access denied" → docker login or check image name
│   └── "manifest unknown" → Verify tag exists in registry
├── Volume mount error?
│   ├── "permission denied" → Match UID/GID or fix ownership
│   ├── Named volume not declared → Add to top-level volumes:
│   └── External volume missing → Create it first
└── Environment variable error?
    ├── "variable is not set" → Define in .env or environment
    └── Wrong value resolved → Check precedence order

Orphan Container Warnings

"Found orphan containers"
├── Service removed from compose.yaml → docker compose down --remove-orphans
├── Project name changed → Use consistent -p flag or COMPOSE_PROJECT_NAME
└── Suppress warning → Set COMPOSE_IGNORE_ORPHANS=true

Error Diagnostic Table

Common Patterns

Proper Service Dependencies with Healthcheck

services:
  app:
    image: myapp:latest
    depends_on:
      db:
        condition: service_healthy
      redis:
        condition: service_healthy

  db:
    image: postgres:16
    healthcheck:
      test: ["CMD-SHELL", "pg_isready -U postgres"]
      interval: 10s
      timeout: 5s
      retries: 5
      start_period: 30s

  redis:
    image: redis:7-alpine
    healthcheck:
      test: ["CMD", "redis-cli", "ping"]
      interval: 10s
      timeout: 5s
      retries: 3

Safe Port Mapping

ports:
  # ALWAYS quote port mappings to prevent YAML parsing issues
  - "8080:80"
  # Bind to localhost for development
  - "127.0.0.1:5432:5432"

Environment Variable with Required Check

environment:
  DATABASE_URL: ${DATABASE_URL:?DATABASE_URL must be set}
  LOG_LEVEL: ${LOG_LEVEL:-info}

Validation Workflow

# Step 1: Validate syntax and variable resolution
docker compose config -q

# Step 2: Start with build and force recreation
docker compose up --build --force-recreate -d

# Step 3: Check service status
docker compose ps

# Step 4: Check logs for failing services
docker compose logs --tail 50 <service-name>

Profile Dependency Resolution

When a profiled service depends on another profiled service, both profiles must be active or the dependency must have no profile:

services:
  app:
    image: myapp

  debug-tools:
    image: debug:latest
    profiles: [debug]
    depends_on:
      - app           # OK: app has no profile, always available

  test-runner:
    image: test:latest
    profiles: [test]
    depends_on:
      - debug-tools   # FAILS unless debug profile is also active

Fix: Either activate both profiles (--profile test --profile debug), remove the cross-profile dependency, or remove the profile from the dependency.

Reference Links

• references/diagnostics.md -- Complete error message to cause to solution mapping
• references/examples.md -- Common Compose error scenarios with step-by-step fixes
• references/anti-patterns.md -- Compose configuration mistakes and corrections

Official Sources

• https://docs.docker.com/compose/compose-file/
• https://docs.docker.com/compose/compose-file/05-services/
• https://docs.docker.com/compose/how-tos/environment-variables/variable-interpolation/
• https://docs.docker.com/compose/how-tos/profiles/
• https://docs.docker.com/reference/cli/docker/compose/