dokcer cluster golang build

In the field of cloud computing, container technology is favored for its lightweight, fast operation, portability and efficiency. As a representative of container technology, Docker has become a popular tool in cloud computing, DevOps and other fields by providing a lightweight way to package and deploy applications. For enterprise-level applications, Docker clusters are needed to achieve high availability, elastic scaling and other functions. This article introduces how to use Golang to build a Docker cluster.

1. Overview of Docker cluster

Docker cluster refers to the cooperation of multiple Docker hosts to achieve functions such as deployment, management and monitoring of applications. Docker clusters usually consist of the following basic concepts:

1. Docker host

Docker host refers to the computer or virtual machine running the Docker engine. Each Docker host can deploy and run multiple Docker containers.

2. Docker Swarm

Docker Swarm is a container orchestration tool officially provided by Docker. It can manage containers on multiple Docker hosts and implement it by defining concepts such as services and tasks. Application deployment and management.

3. Service

Service is a group of containers in a Docker cluster with common functions and specifications, such as Web services, database services, etc. Service can define multiple replica instances to achieve functions such as high availability and load balancing.

4. Task

Task is an instance of Service, that is, a container running on a certain Docker host. Tasks can be scheduled and managed by Docker Swarm to realize automated deployment and management of containers.

5. Node

Node is a Docker host in the Docker cluster and can run multiple Tasks and Services.

2. Golang implements Docker Swarm

Docker Swarm provides RESTful API and CLI tools to manage and control Docker clusters. Golang, as an efficient, concurrent, cross-platform programming language, is widely used in system programming and network programming. The following describes how to use Golang to implement the basic functions of Docker Swarm.

1. Install Docker SDK for Golang

Docker SDK for Golang is the official client provided by Docker and can easily communicate with the Docker server. Docker SDK for Golang can be installed using the following command:

go get -u github.com/docker/docker/client

2. Implementing Docker Swarm API encapsulation

The Docker Swarm API can be called through HTTP requests and returns data in JSON format. We can use Golang to encapsulate the Docker Swarm API for quick and convenient calls. For example, define the following structure:

type SwarmClient struct {
    cli *client.Client
    ctx context.Context
}

type SwamService struct {
    ID string `json:"ID"`
    Name string `json:"Name"`
    Endpoint Endpoint `json:"Endpoint"`
}

type Endpoint struct {
    Spec EndpointSpec `json:"Spec"`
}

type EndpointSpec struct {
    Ports []PortConfig `json:"Ports"`
}

type PortConfig struct {
    Protocol string `json:"Protocol"`
    TargetPort uint32 `json:"TargetPort"`
    PublishedPort uint32 `json:"PublishedPort"`
}

We can use Golang's HTTP package to implement corresponding HTTP request operations such as GET, POST, PUT, and DELETE.

3. Implement Docker Swarm CLI tool

In addition to using RESTful API calls, we can also implement Docker Swarm CLI tool to facilitate Docker Swarm cluster more intuitively management and operations. For example, implement the following command:

docker-swarm service create [OPTIONS] IMAGE [COMMAND] [ARG...]

This command can create a Service service using the specified image and command parameters. We can use Golang to implement corresponding operations, for example:

func createService(image string, command []string, port uint32)  {
    service := &swarm.ServiceSpec{
        TaskTemplate: swarm.TaskSpec{
            ContainerSpec: swarm.ContainerSpec{
                Image: image,
                Command: command,
                Env: []string{"PORT=" + strconv.Itoa(int(port))},
            },
        },
        EndpointSpec: &swarm.EndpointSpec{
            Ports: []swarm.PortConfig{
                swarm.PortConfig{
                    Protocol:      swarm.PortConfigProtocolTCP,
                    TargetPort:    uint32(port),
                    PublishedPort: uint32(port),
                },
            },
        },
    }

    cli, ctx := initCli()
    serviceCreateResponse, err := cli.ServiceCreate(ctx, *service, types.ServiceCreateOptions{})
    if err != nil {
        panic(err)
    }
}

This function can use Docker SDK for Golang to create a Service service and specify parameters such as image, command and port.

4. Implement monitoring and logging of the Docker Swarm cluster

During the running process of the Docker Swarm cluster, we need to monitor it in real time and view the logs. We can use Golang to implement corresponding programs and obtain cluster status and container logs by using the API provided in Docker SDK for Golang. For example:

func listServices() {
    cli, ctx := initCli()
    services, err := cli.ServiceList(ctx, types.ServiceListOptions{})
    if err != nil {
        panic(err)
    }
    for _, service := range services {
        fmt.Printf("[Service] ID:%s Name:%s
", service.ID, service.Spec.Name)
    }
}

func getServiceLogs(serviceID string) {
    cli, ctx := initCli()
    reader, err := cli.ServiceLogs(ctx, serviceID, types.ContainerLogsOptions{})
    if err != nil {
        panic(err)
    }
    defer reader.Close()
    scanner := bufio.NewScanner(reader)
    for scanner.Scan() {
        fmt.Println(scanner.Text())
    }
}

The above code implements operations such as obtaining the Service list in the Docker Swarm cluster and obtaining the logs of the specified Service.

3. Use Docker Compose to implement Docker Swarm cluster

Docker Compose is a container orchestration tool provided by Docker, which can manage multiple containers and services by defining compose files. We can use Docker Compose to quickly build and manage Docker Swarm clusters. For example, define the following compose file:

version: '3'
services:
  web:
    image: nginx
    deploy:
      mode: replicated
      replicas: 3
      resources:
        limits:
          cpus: "0.1"
          memory: 50M
        reservations:
          cpus: "0.05"
          memory: 30M
      restart_policy:
        condition: on-failure
        delay: 5s
        max_attempts: 3
    ports:
      - "80:80"
    networks:
      - webnet
  visualizer:
    image: dockersamples/visualizer:stable
    ports:
      - "8080:8080"
    stop_grace_period: 30s
    volumes:
      - /var/run/docker.sock:/var/run/docker.sock
    deploy:
      placement:
        constraints: [node.role == manager]
    networks:
      - webnet

networks:
  webnet:

This compose file defines a web service and a visualization tool, using the nginx image and dockersamples/visualizer image as services. Among them, the Web service usage mode is replicated service deployment method, which will use 3 replica instances, and set CPU and memory resource limits, restart policy and other configurations. The visualization tool uses the Docker host node with node.role as manager as the deployment node to easily view the Docker Swarm cluster status.

We can use the following command to start Docker Compose:

docker stack deploy -c docker-compose.yml webapp

This command will create the corresponding Service and Task instances based on the configuration items defined in the compose file, and start the Docker Swarm cluster. We can view the real-time status of the Docker Swarm cluster by accessing http://localhost:8080.

Summary

This article introduces how to use Golang to implement the basic functions of a Docker Swarm cluster and how to use Docker Compose to quickly build and manage a Docker Swarm cluster. In practical applications, Docker Swarm clusters can provide high availability, elastic scaling and other functions, and can achieve efficient management and deployment of containerized applications.

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