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.

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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

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Error Diagnostic Table

Error Message	Cause	Fix
yaml: line N: did not find expected key	YAML indentation or syntax error	Check line N for tabs (use spaces), missing colons, or unquoted special characters
services is required	Missing services: top-level key	Add services: as the top-level element
service "X" refers to undefined network "Y"	Network used but not declared	Add network Y to top-level networks: section
service "X" refers to undefined volume "Y"	Named volume used but not declared	Add volume Y to top-level volumes: section
port is already allocated	Host port in use by another container or process	Find occupant: lsof -i :PORT or ss -tlnp | grep PORT. Use a different host port
Bind for 0.0.0.0:PORT failed	Same as above — port conflict	Same fix as above
dependency "X" is not a valid service	depends_on references nonexistent service	Check service name spelling in depends_on
Found orphan containers	Services removed or project name changed	Run docker compose down --remove-orphans
variable "X" is not set	Interpolation variable undefined	Define in .env file, or use ${X:-default} syntax
invalid interpolation format	Malformed variable syntax	Check for unescaped $. Use $$ for literal dollar sign
build path /path does not exist	Build context directory missing	Verify context: path exists relative to compose.yaml
Cannot locate specified Dockerfile	Dockerfile path wrong	Check dockerfile: is relative to context:, not compose.yaml
pull access denied for X	Image not found or authentication required	Run docker login. Verify image name and tag
no matching manifest for linux/amd64	Image not available for platform	Add platform: to service or use compatible image
service "X" has neither an image nor a build context	Service needs image or build	Add image: or build: to the service definition
"version" is obsolete	Deprecated version field	Remove the version: line entirely
invalid service name "X"	Service name contains invalid characters	Use only [a-zA-Z0-9._-], start with letter or digit
Compose file not found	No compose.yaml in directory	Create compose.yaml or use -f flag to specify path
container name "X" is already in use	Stale container with same name exists	Run docker compose down first, or docker rm X
network X declared as external but could not be found	External network does not exist	Create it: docker network create X
volume X declared as external but not found	External volume does not exist	Create it: docker volume create X

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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>

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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.

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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/