Docker Docker Logging and Monitoring Container Metrics docker stats

1. Core Command / Concept

Monitor container resource usage with docker stats.

2. Step-by-Step

1. Check if Docker is running: docker ps
2. Run docker stats with default output: docker stats
3. Run docker stats with detailed output: docker stats --format "table {{.Name}}\t{{.CPUPerc}}\t{{.MemUsage}}"
4. Filter by container name: docker stats --format "table {{.Name}}\t{{.CPUPerc}}\t{{.MemUsage}}" --no-stream
5. ⚠️ Delete all stopped containers: docker rm $(docker ps -a -q -f status=exited)
6. Clean up by removing all unused networks: docker network rm $(docker network ls -q -f isolated=true)

3. Real Commands with Examples

1. Purpose: Monitor CPU usage of a running container.
   Command: docker stats --format "table {{.Name}}\t{{.CPUPerc}}"
   Flags: --format sets the output format, table is the format type, and {{.Name}} and {{.CPUPerc}} are placeholders for the container name and CPU usage percentage, respectively.

2. Purpose: Monitor memory usage of a running container.
   Command: docker stats --format "table {{.Name}}\t{{.MemUsage}}"
   Flags: Same as above, but with {{.MemUsage}} placeholder for memory usage.

3. Purpose: Monitor both CPU and memory usage of a running container.
   Command: docker stats --format "table {{.Name}}\t{{.CPUPerc}}\t{{.MemUsage}}"
   Flags: Same as above, but with both {{.CPUPerc}} and {{.MemUsage}} placeholders.

4. Common Errors

1. Error: docker stats returns an empty output.
   Why: No containers are running.
   Fix: Run docker ps to check if containers are running.

2. Error: docker stats returns an error message.
   Why: Docker is not running or not properly configured.
   Fix: Run docker --version to check if Docker is installed and running, or docker start to start Docker.

3. Error: docker stats returns an error message when filtering by container name.
   Why: The container does not exist or is not running.
   Fix: Run docker ps to check if the container is running, or docker ps -a to check if it exists.

4. Error: docker rm returns an error message when deleting stopped containers.
   Why: The containers are not stopped or do not exist.
   Fix: Run docker ps -a to check if the containers are stopped, or docker ps to check if they exist.

5. Quick Checks

1. Situation: A container is running and consuming high CPU resources.
   Command: docker stats --format "table {{.Name}}\t{{.CPUPerc}}"
   Correct Response: The container name and CPU usage percentage are displayed.

2. Situation: A container is running and consuming high memory resources.
   Command: docker stats --format "table {{.Name}}\t{{.MemUsage}}"
   Correct Response: The container name and memory usage percentage are displayed.

3. Situation: A container is not running.
   Command: docker stats
   Correct Response: An empty output is displayed.

6. Last-Minute Reference

• docker stats command is available in Docker 1.13 and later versions.
• --format flag is used to set the output format.
• table is the default output format.
• {{.Name}}, {{.CPUPerc}}, and {{.MemUsage}} are placeholders for container name, CPU usage percentage, and memory usage percentage, respectively.
• --no-stream flag is used to disable streaming output.
• docker stats command returns an empty output if no containers are running.
• docker stats command returns an error message if Docker is not running or not properly configured.
• docker rm command deletes all stopped containers by default.
• docker network rm command removes all unused networks.
• docker ps command lists all running containers.
• docker ps -a command lists all containers, including stopped ones.