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5.11 Set container CPU priority appropriately

Information

By default, all containers on a Docker host share the resources equally. By using the resource management capabilities of Docker host, such as CPU shares, you can control the host CPU resources that a container may consume.By default, CPU time is divided between containers equally. If it is desired, to control the CPU time amongst the container instances, you can use CPU sharing feature. CPU sharing allows to prioritize one container over the other and forbids the lower priority container to claim CPU resources more often. This ensures that the high priority containers are served better.

Solution

Manage the CPU shares between your containers. To do so start the container using '-c' or '--cpu-shares' argument. You may start the container as below-
$>docker run <Run arguments> --cpu-shares <CPU shares> <Container Image Name or ID> <Command>
For example,
docker run --interactive --tty --cpu-shares 512 centos /bin/bash
In the above example, the container is started with a CPU shares of 50% of what the other containers use. So, if the other container has CPU shares of 80%, this container will have CPU shares of 40%.

Note- Every new container will have1024shares of CPU by default. However, this value is shown as '0' if you run the command mentioned in the audit section.
Alternatively,
1. Navigate to/sys/fs/cgroup/cpu/system.slice/directory.
2. Check your container instance ID using 'docker ps' command.
3. Now, inside the above directory (in step 1), you would have a directory by name 'docker-<Instance ID>.scope' for example 'docker-4acae729e8659c6be696ee35b2237cc1fe4edd2672e9186434c5116e1a6fbed6.scope'. Navigate to this directory.
4. You will find a file named 'cpu.shares'. Execute 'cat cpu.shares'. This will always give you the CPU share value based on the system. So, even if there are no CPU shares configured using '-c' or '--cpu-shares' argument in the 'docker run' command, this file will have a value of '1024'.
If we set one containers CPU shares to 512 it will receive half of the CPU time compared to the other container. So, take 1024 as 100% and then do quick maths to derive the number that you should set for respective CPU shares. For example, use 512 if you want to set 50% and 256 if you want to set 25%.
Impact-
If you do not set proper CPU shares, the container process may have to starve if the resources on the host are not available. If the CPU resources on the host are free, CPU shares do not place any restrictions on the CPU that the container may use.
Default Value-
By default, all containers on a Docker host share the resources equally. No CPU shares are enforced.

See Also

https://workbench.cisecurity.org/files/516

Item Details

Category: SYSTEM AND COMMUNICATIONS PROTECTION

References: 800-53|SC-6

Plugin: Unix

Control ID: de6a6ce84c522a237fd23d028e484bf95cbd4491f6e57612f57dc6dc498e5b5e