ReddRadar
Agent skill
docker-debugging
Container debugging and troubleshooting techniques for production issues
Install this agent skill to your Project
npx add-skill https://github.com/pluginagentmarketplace/custom-plugin-docker/tree/main/skills/docker-debugging
SKILL.md
Docker Debugging Skill
Master container debugging and troubleshooting for development and production issues.
Purpose
Diagnose and resolve container issues including crashes, performance problems, networking failures, and resource constraints.
Parameters
| Parameter | Type | Required | Default | Description |
|---|---|---|---|---|
| container | string | No | - | Container name/ID |
| issue_type | enum | No | - | crash/network/resource/health |
| verbose | boolean | No | false | Detailed output |
Debugging Commands
Container Logs
# Last 100 lines
docker logs --tail 100 <container>
# Follow logs
docker logs -f <container>
# With timestamps
docker logs -t <container>
# Specific time range
docker logs --since 1h --until 30m <container>
Interactive Debugging
# Execute shell in running container
docker exec -it <container> /bin/sh
# As root (for debugging)
docker exec -u 0 -it <container> /bin/sh
# Run command
docker exec <container> ps aux
Container Inspection
# Full inspection
docker inspect <container>
# Specific fields
docker inspect --format='{{.State.Status}}' <container>
docker inspect --format='{{.State.Health.Status}}' <container>
docker inspect --format='{{json .NetworkSettings}}' <container>
Issue Diagnosis
Container Won't Start
# Check exit code
docker inspect --format='{{.State.ExitCode}}' <container>
# View last logs
docker logs --tail 50 <container>
# Check events
docker events --filter 'container=<name>' --since 1h
Exit Code Reference
| Code | Meaning | Action |
|---|---|---|
| 0 | Success | Normal exit |
| 1 | General error | Check logs |
| 137 | OOMKilled | Increase memory |
| 139 | Segfault | Check app code |
| 143 | SIGTERM | Graceful shutdown |
Health Check Failures
# Check health status
docker inspect --format='{{json .State.Health}}' <container>
# View health logs
docker inspect --format='{{range .State.Health.Log}}{{.Output}}{{end}}' <container>
# Manually test health
docker exec <container> curl -f http://localhost/health
Resource Issues
# Live stats
docker stats <container>
# Formatted output
docker stats --format "table {{.Name}}\t{{.CPUPerc}}\t{{.MemUsage}}\t{{.NetIO}}"
# Check limits
docker inspect --format='{{.HostConfig.Memory}}' <container>
Network Issues
# Check network
docker network inspect <network>
# Test DNS
docker exec <container> nslookup <service>
# Test connectivity
docker exec <container> ping -c 3 <target>
docker exec <container> curl http://<service>:port
# View ports
docker port <container>
Troubleshooting Flowchart
Container Issue?
│
├─ Won't Start
│ ├─ Check logs: docker logs <c>
│ ├─ Check exit code: docker inspect
│ └─ Verify image: docker pull
│
├─ Unhealthy
│ ├─ Check health logs
│ ├─ Test health endpoint manually
│ └─ Increase start_period
│
├─ High Resource
│ ├─ Check stats: docker stats
│ ├─ Increase limits
│ └─ Profile application
│
└─ Network Failed
├─ Check DNS: nslookup
├─ Check connectivity: ping/curl
└─ Verify network membership
Debug Container
# Run debug container in same network
docker run --rm -it --network <network> \
nicolaka/netshoot
# Available tools: curl, dig, nmap, tcpdump, etc.
Error Handling
Common Errors
| Error | Cause | Solution |
|---|---|---|
container not found |
Wrong name/ID | Use docker ps -a |
exec failed |
Container stopped | Start container first |
no such file |
Missing binary | Use correct image |
Usage
Skill("docker-debugging")
Assets
assets/debug-commands.yaml- Command referencescripts/container-health-check.sh- Health check script
Related Skills
- docker-production
- docker-networking
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