Menu
By default, Docker does not apply any CPU limitations. Containers can all of the hosts given CPU power. Relax, a Docker container will not consume the entire CPU power of your physical host. If you are using Docker Desktop, the host I mentioned, it is a virtualized host, responsible for running your Docker containers.
By default, a container has no resource constraints and can use as much of a given resource as the host's kernel scheduler allows. Docker provides ways to control how much memory, or CPU a container can use, setting runtime configuration flags of the docker run command.
We can get CPU usage of docker container with docker stats command. The column CPU % will give the percentage of the host's CPU the container is using.
The cpu-shares option allows you to specify the relative share of cpu a container will receive when there is contention for cpu. When there is no contention for cpu, a container will get to use however much it wants, no matter what the 'limit' is.
As Charles mentions, by default all can be used, or you can limit it per container using the --cpuset-cpus parameter.
docker run --cpuset-cpus="0-2" myapp:latest
That would restrict the container to 3 CPU's (0, 1, and 2). See the docker run docs for more details.
The preferred way to limit CPU usage of containers is with a fractional limit on CPUs:
docker run --cpus 2.5 myapp:latest
That would limit your container to 2.5 cores on the host.
Lastly, if you run docker inside of a VM, including Docker for Mac, Docker for Windows, and docker-machine, those VM's will have a CPU limit separate from your laptop itself. Docker runs inside of that VM and will use all the resources given to the VM itself. E.g. with Docker for Mac you have the following menu:
Maybe your host VM has only one core by default. Therefore you should increase your VM cpu-count first and then use --cpuset-cpus option to increase your docker cores. You can remove docker default VM using the following command then you can create another VM with optional cpu-count and memory size.:
docker-machine rm default
docker-machine create -d virtualbox --virtualbox-cpu-count=8 --virtualbox-memory=4096 --virtualbox-disk-size=50000 default
After this step you can specify number of cores before running your image. this command will use 4 cores of total 8 cores.
docker run -it --cpuset-cpus="0-3" your_image_name
Then you can check number of available core in your image using this command:
nproc
If you love us? You can donate to us via Paypal or buy me a coffee so we can maintain and grow! Thank you!
Donate Us With