How to implement docker in golang

Golang (also known as Go) is an open source programming language developed by Google. It is widely welcomed by developers for its efficient concurrency mechanism and fast compilation speed. Docker is a useful containerization technology that makes it easy to package applications and their dependencies into portable images that can be deployed and run in different environments. So, how does Golang implement Docker?

Why use Golang to implement Docker?

In fact, Docker can be implemented in any programming language, but why use Golang? The advantages of Golang are its fast compilation speed, memory safety and fewer dependencies. This makes Golang ideal for large-scale, complex applications and system-level development. Docker is a technology for large-scale and complex applications, so it is very suitable to use Golang to implement Docker.

Golang implements the core principle of Docker

The core principle of Docker is to use Linux containers to isolate applications and their dependencies, thereby achieving application portability and scalability. The core of Golang's implementation of Docker is to use Linux namespace and cgroup to isolate containers and resources.

1. Namespace

Linux namespace is an isolation mechanism that can separate the running environment of a process so that different processes can run on the same machine. Isolate from each other. Docker uses namespace to isolate containers. Specifically, Docker uses the following 6 namespaces:

• PID namespace, used to isolate process IDs;
• Network namespace, used to isolate network interfaces, IP addresses, routing tables, etc. Network resources;
• Mount namespace, used to isolate file system mount points;
• UTS namespace, used to isolate host names and domain names;
• IPC namespace, used to isolate systems IPC;
• User namespace, used to isolate users and groups.

2. Cgroup

Linux's cgroup is a resource management mechanism that can limit the resource usage of different processes within a certain range. Docker uses cgroups to limit the resource usage of containers, such as CPU, memory, disk IO and network bandwidth.

How Golang uses Namespace and Cgroup to implement Docker

In Golang, using Linux namespace and cgroup to implement container isolation and resource limitation requires the use of the following Golang packages:

• os/exec package, used to execute system commands;
• syscall package, used to call Linux system calls;
• golang.org/x/sys/unix package, used to call Constants and data structures called by Linux system;
• cgroupfs package, used to manage cgroups.

The following is the core code for Golang to implement Docker:

package main

import (
    "os/exec"
    "syscall"
    "os"
)

func main() {
    cmd := exec.Command("sh")
    cmd.SysProcAttr = &syscall.SysProcAttr{
        Cloneflags: syscall.CLONE_NEWUTS | syscall.CLONE_NEWPID | syscall.CLONE_NEWNS,
    }
    cmd.Stdin = os.Stdin
    cmd.Stdout = os.Stdout
    cmd.Stderr = os.Stderr
    err := cmd.Run()
    if err != nil {
        panic(err)
    }
}

This code uses the os/exec package and syscall package to call Linux system commands and system calls, creating a new process , and execute a shell command in it. The key is to set the Cloneflags attribute of the syscall.SysProcAttr structure to isolate the UTS namespace, PID namespace and Mount namespace of the process, thus achieving container isolation.

In addition to the namespace used in the above code, other namespaces can also be used to achieve stricter container isolation, such as User namespace, IPC namespace and Network namespace, etc.

Cgroup management can be achieved using the cgroupfs package, which provides a set of functions that can operate Linux cgroups. Through these functions, you can limit the container's resource usage such as CPU, memory, disk IO, and network bandwidth.

Summary

Golang can use Linux namespace and cgroup to implement the core functions of Docker, namely container isolation and resource limitation. For those large-scale applications and system-level development projects that require efficiency, scalability, and security, using Golang to implement Docker is a very suitable choice. Although this is just a minimalist implementation of Docker, its core principles and technical implementation are of great reference value.

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