Resource monitoring per container in Docker - Cheat Sheet & Quick Revision

Recall & Review

beginner

What command shows real-time resource usage of all running Docker containers?

The command docker stats displays live CPU, memory, network, and disk I/O usage for all running containers.

intermediate

How can you limit the CPU usage of a Docker container?

Use the --cpus flag when running a container, for example: docker run --cpus=1.5 limits the container to 1.5 CPU cores.

beginner

What does the docker stats output column 'MEM USAGE / LIMIT' represent?

It shows the current memory used by the container and the maximum memory allowed (limit) if set.

beginner

How to monitor resource usage of a specific container only?

Run docker stats <container_id_or_name> to see resource usage for just that container.

beginner

What is the purpose of setting resource limits on containers?

Resource limits prevent a container from using too much CPU or memory, helping keep the host system stable and fair to other containers.

Which Docker command shows live CPU and memory usage of containers?

A docker inspect

B docker ps

C docker logs

D docker stats

docker stats shows live resource usage like CPU and memory for containers.

How do you limit a container to use only 2 CPUs?

A docker run --cpus=2

B docker run --memory=2

C docker run --cpu-limit=2

D docker run --limit-cpu=2

The --cpus flag limits CPU cores, so --cpus=2 restricts to 2 CPUs.

What does the 'NET I/O' column in docker stats show?

A Network input and output data usage

B CPU network priority

C Number of network interfaces

D Network latency

'NET I/O' shows how much data the container has sent and received over the network.

To monitor only one container's resource usage, you should:

A docker logs <container_name_or_id>

B docker ps <container_name_or_id>

C docker stats <container_name_or_id>

D docker inspect <container_name_or_id>

docker stats with container ID or name shows resource usage for that container only.

Why is it important to set resource limits on containers?

A To speed up container startup time

B To prevent containers from using too many resources and affecting other containers or the host

C To increase container storage space

D To enable container networking

Resource limits keep containers from overusing CPU or memory, protecting system stability.

Explain how to monitor resource usage for Docker containers and why it is useful.

Think about commands and what information they show.

Describe how to set CPU and memory limits on a Docker container and the benefits of doing so.

Consider the flags used when running containers.

Practice

1. What does the docker stats command show for each running container?

easy

A. The container's file system contents

B. The container's log output

C. Live resource usage like CPU, memory, network, and disk I/O

D. The container's environment variables

Solution

1. Step 1: Understand the purpose of docker stats

   The docker stats command is designed to show live resource usage statistics for running containers.

2. Step 2: Identify the resources monitored

   It monitors CPU, memory, network I/O, and disk I/O per container to help track performance.

3. Final Answer:

   Live resource usage like CPU, memory, network, and disk I/O -> Option C

4. Quick Check:

   docker stats = Live resource usage [OK]

Hint: Remember: docker stats shows live resource use per container [OK]

Common Mistakes:

• Confusing docker stats with docker logs
• Thinking it shows file system contents
• Assuming it shows environment variables

2. Which of the following is the correct command to show live resource usage for all running Docker containers?

easy

A. docker stats

B. docker monitor

C. docker inspect stats

D. docker top

Solution

1. Step 1: Recall the command for resource monitoring

   The command docker stats is the official Docker command to show live resource usage for containers.

2. Step 2: Verify other options

   docker monitor and docker inspect stats are invalid commands, and docker top shows running processes, not resource stats.

3. Final Answer:

   docker stats -> Option A

4. Quick Check:

   Correct command = docker stats [OK]

Hint: Use 'docker stats' to see live container resource use [OK]

Common Mistakes:

• Using docker top to check resource usage
• Trying docker monitor which doesn't exist
• Confusing docker inspect with stats

3. You run docker stats --no-stream on a container. What will you see?

medium

A. Continuous live updates of resource usage

B. A single snapshot of current resource usage

C. Only CPU usage without memory info

D. Error because --no-stream is invalid

Solution

1. Step 1: Understand the --no-stream option

   The --no-stream option tells docker stats to show resource usage only once, not continuously.

2. Step 2: Identify the output behavior

   It outputs a single snapshot of CPU, memory, network, and disk I/O usage at the moment the command runs.

3. Final Answer:

   A single snapshot of current resource usage -> Option B

4. Quick Check:

   --no-stream = single snapshot [OK]

Hint: Use --no-stream for one-time resource snapshot [OK]

Common Mistakes:

• Expecting continuous updates with --no-stream
• Thinking it shows only CPU usage
• Assuming --no-stream is invalid

4. You try to run docker stats --format '{{.CPUPerc}} but get no output. What is the likely problem?

medium

A. The format string is missing a closing single quote

B. The container is stopped, so no stats show

C. The --format option is not supported in docker stats

D. You need to add --no-stream to see output

Solution

1. Step 1: Check the format string syntax

   The command uses --format '{{.CPUPerc}} which is missing the closing single quote after the curly braces.

2. Step 2: Understand impact of missing quote

   Without the closing quote, the shell or Docker cannot parse the format string, so no output appears.

3. Final Answer:

   The format string is missing a closing single quote -> Option A

4. Quick Check:

   Format string syntax error = missing quote [OK]

Hint: Always close quotes in --format strings [OK]

Common Mistakes:

• Assuming stopped containers show no stats (they do not appear in stats)
• Thinking --format is unsupported
• Believing --no-stream is required for output

5. You want to monitor CPU and memory usage of a specific container named webapp and save the output once to a file. Which command should you use?

hard

A. docker stats --stream=false webapp > usage.txt

B. docker stats webapp --output usage.txt

C. docker monitor webapp > usage.txt

D. docker stats --no-stream --format 'table {{.Name}}\t{{.CPUPerc}}\t{{.MemUsage}}' webapp > usage.txt

Solution

1. Step 1: Choose the correct command and options

   To get a one-time snapshot, use --no-stream. To format output with container name, CPU, and memory, use --format with a table layout.

2. Step 2: Redirect output to a file

   Use shell redirection > usage.txt to save the output to a file named usage.txt.

3. Final Answer:

   docker stats --no-stream --format 'table {{.Name}}\t{{.CPUPerc}}\t{{.MemUsage}}' webapp > usage.txt -> Option D

4. Quick Check:

   One-time formatted output saved to file = docker stats --no-stream --format 'table {{.Name}}\t{{.CPUPerc}}\t{{.MemUsage}}' webapp > usage.txt [OK]

Hint: Use --no-stream and --format, redirect output to file [OK]

Common Mistakes:

• Using invalid docker monitor command
• Assuming --output option exists
• Using --stream=false instead of --no-stream