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ln-783-container-launcher
Type: L3 Worker Category: 7XX Project Bootstrap Parent: ln-780-bootstrap-verifier
Purpose
Builds Docker images, launches containers, and performs comprehensive health verification using Docker native health checks and retry strategies.
Scope:
- Detect and validate docker-compose.yml configuration
- Build Docker images
- Launch containers with proper startup order
- Verify container health using native health checks
- Provide access URLs and cleanup instructions
Out of Scope:
- Building application code (handled by ln-781)
- Running tests (handled by ln-782)
- Container orchestration beyond single host (Kubernetes, Swarm)
When to Use
| Scenario | Use This Skill | |----------|---------------| | Called by ln-780 orchestrator | Yes | | Standalone container launch | Yes | | Development environment setup | Yes | | Production deployment | No, use proper CI/CD |
Workflow
Step 1: Pre-flight Checks
Verify Docker environment readiness.
| Check | Failure Action | |-------|---------------| | Docker daemon running | Report error with installation instructions | | Docker Compose available | Report error, suggest installation | | Compose file exists | Report error, list expected locations | | Required ports free | Report conflict, suggest alternatives | | Sufficient disk space | Warn if low space (<2GB free) |
Step 2: Parse Compose Configuration
Extract service information from docker-compose.yml.
| Information | Purpose | |-------------|---------| | Service names | Track which containers to monitor | | Exposed ports | Know which ports to check | | Health check definitions | Use native health checks if defined | | Dependencies (depends_on) | Understand startup order | | Volume mounts | Verify paths exist |
Step 3: Build Images
Build all images defined in compose file.
| Aspect | Strategy | |--------|----------| | Build context | Use paths from compose file | | Build args | Pass through from compose configuration | | Cache | Use Docker layer cache for speed | | Failure | Report build errors with full log |
Step 4: Launch Containers
Start containers with proper orchestration.
| Aspect | Strategy | |--------|----------| | Startup order | Respect depends_on and healthcheck conditions | | Detached mode | Run in background | | Network | Use compose-defined networks | | Volumes | Mount all defined volumes |
Step 5: Health Verification
Verify all containers are healthy using appropriate strategy.
Strategy Selection:
| Condition | Strategy |
|-----------|----------|
| Service has healthcheck: in compose | Use native Docker health status |
| Service has depends_on: condition: service_healthy | Wait for Docker health status |
| No healthcheck defined | Use external HTTP probe with retry |
Retry Configuration:
| Parameter | Value | Rationale | |-----------|-------|-----------| | Max attempts | 10 | Allow slow-starting services | | Initial delay | 5s | Give containers time to start | | Backoff | Exponential (5, 10, 20, 40s) | Avoid overwhelming services | | Max total wait | 120s | Reasonable upper limit |
Health Check Methods:
| Method | When to Use | |--------|------------| | Docker health status | When container has healthcheck defined | | HTTP GET to exposed port | For web services without healthcheck | | Container exec | For services without exposed ports | | TCP port check | For databases and message queues |
Step 6: Report Results
Return structured results to orchestrator.
Result Structure:
| Field | Description | |-------|-------------| | containers | Array of container status objects | | healthChecks | Array of health check results | | accessUrls | Map of service name to access URL | | overallStatus | healthy / unhealthy / partial | | startupDuration | Time from launch to all healthy |
Container Status Object:
| Field | Description | |-------|-------------| | name | Container name | | service | Service name from compose | | status | running / exited / restarting | | health | healthy / unhealthy / starting / none | | port | Exposed port (if any) | | startedAt | Container start timestamp |
Health Check Result:
| Field | Description | |-------|-------------| | url | Checked URL or endpoint | | status | HTTP status code or check result | | responseTime | Time to respond in ms | | healthy | Boolean health status |
Error Handling
| Error Type | Action | |------------|--------| | Docker daemon not running | Report with start instructions | | Port already in use | Report conflict, suggest docker compose down first | | Image build failed | Report with build logs | | Container exited | Report with container logs | | Health check timeout | Report with last known status and logs | | Network unreachable | Check Docker network configuration |
Options
| Option | Default | Description | |--------|---------|-------------| | keepRunning | true | Leave containers running after verification | | stopAfter | false | Stop containers after successful verification | | healthTimeout | 120 | Max seconds to wait for healthy status | | showLogs | true | Show container logs on failure | | buildFirst | true | Build images before starting | | pullLatest | false | Pull base images before build |
Cleanup Instructions
Provide user with cleanup commands in report.
| Action | Description | |--------|-------------| | Stop containers | Stop running containers, preserve data | | Remove containers and networks | Clean up containers but keep volumes | | Remove everything | Full cleanup including volumes and images |
Critical Rules
- Use native health checks when available - more reliable than external probes
- Implement retry with backoff - services need time to initialize
- Always collect logs on failure - essential for debugging
- Parse compose file for ports - do not hardcode port numbers
- Respect depends_on order - critical for database-dependent services
Definition of Done
- [ ] Docker environment verified
- [ ] All images built successfully
- [ ] All containers running
- [ ] All health checks passing
- [ ] Access URLs provided
- [ ] Results returned to orchestrator
Reference Files
- Parent:
../ln-780-bootstrap-verifier/SKILL.md
Version: 2.0.0 Last Updated: 2026-01-10