CODEWITHSUNDEEP
docker
basit khan
basit khan

Reputation: 121

Docker container limiting CPU resources

I have some upstream flask containers and the CPU usage hit 100% percent when i entertain some requests. the system shows that the containers are using your CPU 100%.

My questions are:

  1. If i limit the CPU usage on these containers, will they exit with zero error if they hit there allocated resources OR what are the disadvantages of limiting resources against docker containers?

  2. which one is the better approach in terms of resource allocation to docker containers? (For 6 cpu cores)

    a) Two containers running with default settings. (Use as much resources as the kernel can provide may be)

    b) 4 containers can only use 1 CPU (--limit cpus ='1')

Please let me know if you want me elaborate more.

Thanks in Advance

Upvotes: 1

Views: 2147

Answers (1)

David Maze
David Maze

Reputation: 158908

  1. Containers (and other Linux processes) that try to use more CPU cycles than they have been allocated will just get throttled: the Linux kernel will schedule other processes instead. Going over your CPU limit has no adverse consequences other than your process running slower.

    For example, say your program starts 4 threads and each runs some intensive computation using a full core, but you're running this in a Docker container with --cpus=2. All four threads will run, but the combined program will be limited to 200% CPU, and the overall performance will be similar to if you had only launched 2 threads.

  2. You will usually get better overall system utilization if you don't explicitly limit CPU utilization. If you are running 4 containers, and one of them is running the 4-thread computation job described above but the other three are idle, you will fully use the available system resources if you don't have limits.

    If you do have a specific computationally intensive container, you may want to limit its CPU utilization to not starve out other processes. If you only have the one worker container and three Web server containers, consider limiting the worker to 3 or 3.5 CPUs on a 4-core system to guarantee some spare cycles for HTTP traffic. This is a tuning optimization, so look into it only if you're seeing a problem.

Note that CPU and memory work differently. You can't really use "too much" CPU, since if you wait there will always be more CPU cycles, but the kernel rations out what your process is able to run. On the other hand, memory is fixed, and your process will get killed if it goes over a memory limit.

Upvotes: 3

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