Resource Limits

CPU

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CPU Shares

By default, the Docker Host will assign a CPU share of 1024 to each container. You can modify that by using --cpu-shares option while creating the container.

docker run --cpu-shares=<amount> <image>
docker run --cpu-shares=512 ubuntu

--cpu-shares - It specifies how the host's total CPU resources are shared among its containers.

CPU Sets

It limits the specific CPUs or cores a container can use. A comma-separated list or hyphen-separated range of CPUs a container can use. Let's said that you have more than one CPU. Then the first cpu is numbered 0.

• 1st CPU is numbered 0
• 2nd CPU is numbered 1

Value of 0-3 means, use the first, second, third, and fourth CPU.
Value of 1,3 means, use the second, and fourth CPU.

docker run --cpuset-cpus=<value> <image>
 
# example
docker run --cpuset-cpus=0-1 ubuntu # this container can use first and second CPU
docker run --cpuset-cpus=1,3 ubuntu # this container can use second and fourth CPU

cpuset-cpus - It specifies the CPU numbers to use.

CPU Count

It specifies how much of the available CPU resources a container can use. If host has 2 CPUs and if you set 1 CPU, then the container is guaranteed at most one CPU.

docker run --cpus=<value> <image>
 
# example
# Let's say you have 4 CPUs, you specify 2.5, that means the container can only use as much as 2.5 out of 4.
docker run --cpus=2.5 ubuntu

Memory

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We want to set the maximum amount of memory the container can use.

docker run -m/--memory <size> <image>
 
# example
docker run -m 512m ubuntu
docker run --memory=512m ubuntu

• m = megabytes
• g = gigabytes

So, setting 512m will allocate 512MB of memory for the container. By default, the container will use the same amount of memory that is specified as swap space, that means when the container consumes more than 512MB, it can also consume another 512MB as swap space. Therefore, the container will get 1GB of memory, which effectively combines memory and swap space.

Sum of memory = memory + swap space

You can limit the container's use of swap space by specifying the --memory-swap option while creating the container.

docker run --memory=<size> --memory-swap=<size> <image>
docker run --memory=512m --memory-swap=512m ubuntu

In this case, there is no swap space configured because the --memory and --memory-swap options are the same.

Swap space = 512m - 512m = 0m

If you want to allocate 256 megabytes for swap space, you have to set --memory-swap=768m.

docker run --memory=512m --memory-swap=768m ubuntu

Swap space = 768m - 512m = 256m

Additional add-on

docker run --memory=512m --memory-swap=-1 ubuntu # unlimited memory swap(infinity)
 
# Docker will ensure the memory allocated to this container
docker run --memory=512m --memory-swap=-1 --memory-reservation=100m ubuntu

--memory-reservation = Allows you to specify a soft limit smaller than --memory which is activated when Docker detects contention or low memory on the host machine. It must be set lower than --memory for it to takje precedence. Because it is a soft limit, it doesn't guarantee that the container doesn't exceed the limit.