Docker Container Default Memory Limit: You Should Know!

Estimated reading time: 5 minutes

Last updated on November 8th, 2024 at 05:02 pm

Have you ever wondered how Docker manages memory for the container workload? If the answer is “NO” then you should know!

In this blog, we’ll explore the memory management in the Docker container, the Docker container default memory limit in detail, and the importance of best practices for your application.

Understanding Docker Container Default Memory Limit

What is Docker Container Default Memory Limit?

When you run an application inside the Docker container, the application needs resources such as CPU, Memory, and Storage.

By default, Docker containers have “unlimited memory, ” meaning no resource constraints and use as much as the Host machine allows.

Docker provides a way to limit your application’s memory in the container. This limit ensures that your application container doesn’t use all the available memory and causes problems for the Docker container and the Host machine.

Why Does Docker Set Default Memory Limit?

As mentioned Docker doesn’t restrict any resource usage on containers but it’s recommended to set the memory limits to keep your application container running smoothly.

Docker can prevent containers from taking all available resources and causing “running out of memory” by limiting how much memory a container can use. In other words, make sure everyone gets a fair share!

How to Check the Default Memory Limit?

In Docker, memory limits are enforced using the cgroups, if you want to find the Docker container default memory limit you can check with the below cmd:

# cgroup v1
cat /sys/fs/cgroup/memory/memory.limit_in_bytes

# cgroup v2
cat /sys/fs/cgroup/memory.max

Check the above location in cgroups based on your installation.

Default Memory Limit in Docker: Exploring the Details

Kernel Support

Before setting memory limits, check if your kernel supports Linux capabilities as it’s essential. You can use the handy Docker command docker info to check the support. If the capability is not enabled you may see a warning:

WARNING: No swap limit support

Running Out of Memory

It’s recommended not to allow the running container to consume too much of the Host machine’s memory. Wherever the Linux kernel detects, not enough memory to perform important tasks on the Host, it starts killing the processes to free up the memory.

Running out of memory can lead to the “Out Of Memory Exception (OOME)”. Docker adjusts the OOM priority and reduces the risk of it being killed but individual containers are at risk.

The important thing is to set the appropriate limit ALWAYS!

Adjusting Default Memory Limits

Docker provides additional options to enforce hard and soft memory limits on containers. For Docker container default memory limit you can use --memory or -m option for running a Docker container with a default memory limit.

Hard Memory Limit: Restrict a container memory limit strictly no more than a fixed memory.

Soft Memory Limit: Provide more flexibility for memory but within a safety net, only restrict when low memory.

docker run --memory=<limit> <image_name>

Replace <limit> with the amount of memory you want to allocate to the container, such as “512m” for 512 megabytes or “1g” for 1 gigabyte.

Monitoring and Optimizing Memory Usage

Setting up the initial memory limit is always recommended but it’s also important to keep checking your memory usage. Keep an eye on your memory usage and optimize the usage based on metrics.

Docker provides tools for monitoring memory usage, such as the docker stats command. You can check container resource usage in real-time statistics.

Analyse and optimize the Docker container default memory limit based on data.

docker stats

CONTAINER ID   NAME            CPU %     MEM USAGE / LIMIT    MEM %     NET I/O         BLOCK I/O      PIDS
adf24d3c134a   container1      0.50%     150MiB / 2GiB       7.50%     3.45MB / 9.67MB  2.31MB / 1.23MB   7
bd98e7b821bc   container2      2.30%     210MiB / 2GiB       10.50%    4.21MB / 12.7MB  1.98MB / 1.02MB   8
a1b2c3d4e5f6   container3      1.20%     180MiB / 2GiB       9.00%     2.98MB / 10.3MB  2.15MB / 1.45MB   6

In this example output:

• CONTAINER ID: Unique identifier for each container.
• NAME: Name of the container.
• MEM USAGE / LIMIT: Memory usage of the container compared to its memory limit.
• MEM %: Percentage of memory usage by the container.

Best Practices for Managing Docker Container Memory

To mitigate the risk of instability in the system and Docker container, it’s recommended to to see the Docker container default memory limit:

• Perform a load test to understand your application memory requirements.
• Ensure your application runs on a Host that has enough resources. You can use a combination of host and service labels.
• Limit the amount of memory your Docker container can use.
• Utilize Swap memory, it’s slower than memory but can provide a buffer when running out of memory.

Conclusion

Setting up Docker container default memory is crucial for optimizing resource usage and preventing unexpected behavior. By setting appropriate memory limits you can ensure your application runs smoothly in a Docker container.

Check for the best practices for the Docker container default memory limit and always test your application memory requirements and adjust limits accordingly.

Additional Resources

Docker Container Logs Location: A Comprehensive Guide

Best Practices For Docker Container Naming Convention

Docker Container Security Cheatsheet: Don’t Get Hacked🔐

Hadolint: Comprehensive Guide to Lint Dockerfiles

Docker Build 39x Times Faster: Docker Build Cloud