docker的memory和cpu資源限制

這裏僅針對docker自己，不涉及任何編排工具compose或者k8s等。

按照慣例，官文擼起來。

重要的部分是一些選項，用來限制資源大小。

Memory

Most of these options take a positive integer, followed by a suffix of b, k, m, g, to indicate bytes, kilobytes, megabytes, or gigabytes.

-m or --memory= The maximum amount of memory the container can use. If you set this option, the minimum allowed value is 4m (4 megabyte).
--oom-kill-disable By default, if an out-of-memory (OOM) error occurs, the kernel kills processes in a container. To change this behavior, use the --oom-kill-disable option. Only disable the OOM killer on containers where you have also set the -m/--memory option. If the -m flag is not set, the host can run out of memory and the kernel may need to kill the host system’s processes to free memory.

多數選項值都是正整數，單位是b, k, m, g，分別表示 bytes, kilobytes, megabytes, 和 gigabytes。

-m or --memory= 指定一個容器能使用的最大內存，默認不容許小於4m。
--oom-kill-disable 默認若是發生OOM異常，內核會kill掉容器中的進程。可使用這個選項來改變這種行爲。只在設置了-m內存限制的容器上有效。若是沒有設置-m，宿主機會OOM，而後內核會須要kill宿主機的進程來釋放內存。

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CPU

By default, each container’s access to the host machine’s CPU cycles is unlimited. You can set various constraints to limit a given container’s access to the host machine’s CPU cycles. Most users use and configure the default CFS scheduler.

The CFS is the Linux kernel CPU scheduler for normal Linux processes. Several runtime flags allow you to configure the amount of access to CPU resources your container has. When you use these settings, Docker modifies the settings for the container’s cgroup on the host machine.

--cpus=<value> Specify how much of the available CPU resources a container can use. For instance, if the host machine has two CPUs and you set --cpus="1.5", the container is guaranteed at most one and a half of the CPUs. 
--cpuset-cpus Limit the specific CPUs or cores a container can use. A comma-separated list or hyphen-separated range of CPUs a container can use, if you have more than one CPU. The first CPU is numbered 0. A valid value might be 0-3 (to use the first, second, third, and fourth CPU) or 1,3 (to use the second and fourth CPU).

默認，每一個容器能使用的系統cpu資源是沒有限制的。多數用戶使用默認的CFS調度器來配置。
CFS是linux用於進程的內核cpu調度器。有一些運行時選項能夠用來限制容器可使用的cpu資源，這些配置會修改宿主機上容器的cgroup設置。

--cpus= 指定一個容器可用的cpu資源的大小。例如，若是宿主機有兩個cpu，那麼--cpus="1.5"表示可使用1.5個cpu。
--cpuset-cpus 限制一個容器能使用指定的cpu或cpu核心。能夠用逗號分隔符表示單獨的哪幾個，或者連字符(中橫線)表示範圍。從0開始計數，第一個cpu記爲0。1, 3表示使用第二個和第四個cpu。1-3表示使用第二三四個cpu。

一個簡單示例：

# If you have 1 CPU,  the following command guarantees the container at most 50% of the CPU every second.

docker run -it --cpus=".5" debian:jessie /bin/bash

參考：
https://docs.docker.com/config/containers/resource_constraints/