Linux and Docker: How to implement dynamic scheduling and resource management of containers?

Linux and Docker: How to implement dynamic scheduling and resource management of containers?

Abstract:
With the rapid development and widespread application of container technology, how to better realize the dynamic scheduling and resource management of containers has become an important topic. This article will focus on some common mechanisms and methods in Linux and Docker, as well as sample code, to help readers better understand the dynamic scheduling and resource management of containers.

Introduction:
The rise of container technology has brought revolutionary changes to the deployment and operation of applications. Traditional virtualization technology requires a hypervisor, while container technology can run applications directly on the host machine without the need for additional hypervisors.

The core of container technology is the container engine, the most famous of which is Docker. Docker provides a lightweight and easy-to-use container solution and has become the representative of container technology. This article will take Docker as an example and combine it with the mechanism of the Linux system to introduce how to implement dynamic scheduling and resource management of containers.

1. Container technology in Linux

In Linux systems, container technology mainly relies on two important functions, namely cgroup and namespace. cgroups (control groups) can limit and manage system resources, while namespace can isolate processes and file systems.

1. cgroup

cgroup is a powerful resource configuration and restriction mechanism that can set resource limits for different process groups. By using cgroups, we can specify different resource limits, such as CPU quotas, memory quotas, etc., for processes in the container and external processes. In Linux systems, cgroups are widely used to implement container resource management.

The following is a sample code that uses cgroup to limit the CPU usage of processes within a container:

#!/bin/bash

# 创建cgroup
cgcreate -g cpu:/docker_container

# 设置CPU配额为50%
cgset -r cpu.cfs_quota_us=50000 /docker_container

# 启动容器
docker run -d -it --name=my_container --cgroup-parent=/docker_container ubuntu /bin/bash

In the above example, we use the cgcreate command to create a cgroup named docker_container, and use cgset sets the cgroup's CPU quota to 50%. Then we use the docker command to start a container named my_container and attribute it to the docker_container cgroup. In this way, the CPU usage of the process within the container will be limited to 50%.

2. namespace

namespace can provide an independent running environment for the process, including the file system and process space. By using namespace, we can achieve isolation between the container and the host.

The following is a sample code that uses namespace to isolate a file system in a container:

#define _GNU_SOURCE
#include <sched.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>

int main() {
    // 创建一个新的namespace
    int ret = unshare(CLONE_NEWNS);
    if (ret) {
        perror("unshare");
        exit(EXIT_FAILURE);
    }

    // 在新的namespace中挂载一个文件系统
    ret = mount("rootfs", "/mnt", "ext4", MS_MGC_VAL, NULL);
    if (ret) {
        perror("mount");
        exit(EXIT_FAILURE);
    }

    // 执行容器需要的命令
    system("/bin/bash");

    return 0;
}

In the above example, we use the unshare function to create a new namespace and mount it in it A rootfs file system. Next, we executed a /bin/bash command. This executed command will be run in the new namespace, thus achieving isolation of the file system.

2. Container Scheduling and Resource Management in Docker

In addition to providing containers, Docker also provides some advanced functions, such as dynamic scheduling and resource management of containers. These features make Docker a powerful container management platform.

1. Dynamic scheduling of containers

Docker implements dynamic scheduling of containers by using a scheduler. The scheduler can automatically assign containers to hosts according to different scheduling policies. Commonly used scheduling strategies are:

• Random scheduling: allocate containers to hosts based on random algorithms;
• Load balancing scheduling: allocate containers to the most idle ones based on the load of the host Host;
• Collaborative scheduling:

The following is a sample code for container scheduling using Docker's scheduler:

#!/bin/bash

# 使用负载均衡调度器
docker run -d -p 8080:80 --name=mynginx --scheduler=random nginx

In the above example, We used a load balancing scheduler to assign a container named mynginx to a host. The container will listen on port 8080 of the host and forward the request to port 80 within the container.

2. Resource Management

Docker provides a series of commands and APIs to implement resource management of containers. We can use these features to monitor and manage the resource usage of containers.

The following is a sample code that uses the Docker command to view the resource usage of the container:

#!/bin/bash

# 查看容器的CPU使用情况
docker stats --format "table {{.Container}}    {{.CPUPerc}}    {{.MemUsage}}" my_container

In the above example, we used the docker stats command to view the CPU usage of a container named my_container rate and memory usage.

Conclusion:
This article introduces some common methods and sample codes to implement dynamic scheduling and resource management of containers in Linux and Docker. By using cgroups to implement resource restrictions and namespaces to implement environment isolation, we can better manage and operate containers. Docker further provides advanced features, such as dynamic scheduling and resource management, to help us better utilize container technology. I hope that through the introduction of this article, readers can have a deeper understanding of the dynamic scheduling and resource management of containers.

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