Docker Debugging

# Docker Debugging Commands Reference
# Version: 1.0.0
# Last Updated: 2025-12-29

container_inspection:
  # View container details
  inspect: "docker inspect <container_id>"
  # View running processes
  top: "docker top <container_id>"
  # View resource usage
  stats: "docker stats <container_id> --no-stream"
  # View port mappings
  port: "docker port <container_id>"

log_analysis:
  # View all logs
  all_logs: "docker logs <container_id>"
  # Follow logs in real-time
  follow: "docker logs -f <container_id>"
  # Last N lines
  tail: "docker logs --tail 100 <container_id>"
  # With timestamps
  timestamps: "docker logs -t <container_id>"
  # Since specific time
  since: "docker logs --since 30m <container_id>"

interactive_debugging:
  # Start bash in running container
  exec_bash: "docker exec -it <container_id> /bin/bash"
  # Start sh (if bash not available)
  exec_sh: "docker exec -it <container_id> /bin/sh"
  # Run specific command
  exec_cmd: "docker exec <container_id> <command>"
  # As root user
  exec_root: "docker exec -u root -it <container_id> /bin/bash"

network_debugging:
  # View container networks
  network_inspect: "docker network inspect <network_name>"
  # Test DNS resolution
  dns_test: "docker exec <container_id> nslookup <hostname>"
  # Test connectivity
  ping_test: "docker exec <container_id> ping -c 3 <target>"
  # Check open ports
  netstat: "docker exec <container_id> netstat -tlnp"

resource_analysis:
  # Disk usage
  system_df: "docker system df -v"
  # Container size
  container_size: "docker ps -s"
  # Image layers
  image_history: "docker history <image>"

health_checks:
  # View health status
  health_status: "docker inspect --format='{{.State.Health.Status}}' <container_id>"
  # View health logs
  health_log: "docker inspect --format='{{range .State.Health.Log}}{{.Output}}{{end}}' <container_id>"

common_issues:
  container_not_starting:
    - "Check logs: docker logs <container_id>"
    - "Check exit code: docker inspect -f '{{.State.ExitCode}}' <container_id>"
    - "Review entrypoint/cmd in Dockerfile"

  high_memory_usage:
    - "Check limits: docker stats"
    - "Add memory limit: --memory=512m"
    - "Review application memory leaks"

  network_issues:
    - "Check network mode: docker inspect -f '{{.NetworkSettings.Networks}}' <container_id>"
    - "Verify DNS: docker exec <container_id> cat /etc/resolv.conf"
    - "Test inter-container: docker exec <container_id> ping <other_container>"

#!/bin/bash
# Container Health Check Script
# Version: 1.0.0
# Usage: ./container-health-check.sh <container_id_or_name>

set -e

CONTAINER=${1:-}

if [ -z "$CONTAINER" ]; then
    echo "Usage: $0 <container_id_or_name>"
    exit 1
fi

echo "=========================================="
echo "Container Health Check Report"
echo "Container: $CONTAINER"
echo "Date: $(date)"
echo "=========================================="

# Check if container exists
if ! docker inspect "$CONTAINER" > /dev/null 2>&1; then
    echo "ERROR: Container '$CONTAINER' not found"
    exit 1
fi

# Basic Info
echo ""
echo "--- Basic Information ---"
docker inspect --format='Name: {{.Name}}' "$CONTAINER"
docker inspect --format='Image: {{.Config.Image}}' "$CONTAINER"
docker inspect --format='Status: {{.State.Status}}' "$CONTAINER"
docker inspect --format='Started: {{.State.StartedAt}}' "$CONTAINER"

# Health Status
echo ""
echo "--- Health Status ---"
HEALTH=$(docker inspect --format='{{if .State.Health}}{{.State.Health.Status}}{{else}}no healthcheck{{end}}' "$CONTAINER")
echo "Health: $HEALTH"

if [ "$HEALTH" != "no healthcheck" ]; then
    echo "Last Health Check:"
    docker inspect --format='{{range $i, $h := .State.Health.Log}}{{if eq $i 0}}Exit: {{$h.ExitCode}} - {{$h.Output}}{{end}}{{end}}' "$CONTAINER" 2>/dev/null || echo "No health log available"
fi

# Resource Usage
echo ""
echo "--- Resource Usage ---"
docker stats "$CONTAINER" --no-stream --format "CPU: {{.CPUPerc}} | Memory: {{.MemUsage}} | Net I/O: {{.NetIO}} | Block I/O: {{.BlockIO}}"

# Network Info
echo ""
echo "--- Network Configuration ---"
docker inspect --format='{{range $net, $conf := .NetworkSettings.Networks}}Network: {{$net}} | IP: {{$conf.IPAddress}}{{end}}' "$CONTAINER"

# Port Mappings
echo ""
echo "--- Port Mappings ---"
docker port "$CONTAINER" 2>/dev/null || echo "No ports exposed"

# Recent Logs
echo ""
echo "--- Recent Logs (last 10 lines) ---"
docker logs --tail 10 "$CONTAINER" 2>&1

# Running Processes
echo ""
echo "--- Running Processes ---"
docker top "$CONTAINER" 2>/dev/null || echo "Unable to get process list"

echo ""
echo "=========================================="
echo "Health Check Complete"
echo "=========================================="