Access Docker Using Rest API

Most of the time we use Docker CLI to manage Docker Objects such as containers, images, volumes, and networks. But we Also can use Rest API to Manage Docker objects.

Originally published at https://devkamboj.in.

Docker CLI also uses the Docker rest API to manage Objects. As you can see in the above image. But it is also possible to use the Rest API Directly.

The Docker daemon can listen for Docker Engine API requests via three different types of Socket: unix, tcp, and fd.

By Default, unix socket is enabled. This does not help if you want to access the Docker Rest API remotely. Because unix socket works for exchanging data between processes executing on the same host operating system.
If you need to access the Docker daemon remotely, you need to enable the TCP Socket.

sudo dockerd -H tcp://0.0.0.0:2375

You can listen on port 2375 on all network interfaces with -H tcp://0.0.0.0:2375

There is also another way by using systemd

cd /lib/systemd/system
vi docker.service
ExecStart=/usr/bin/dockerd -H fd:// -H tcp://0.0.0.0:2375
#just add -H tcp://0.0.0.0:2375 and restart docker

Now you can start using the api

curl -X GET http://ip:4243/containers/json
[{
  "Id":"fff8c7927e19d5a7da280424a09572729641137a8f42e116c3073c72da2978d3",
 "Names":["/rockey"],
  "Image":"busybox",
  ...
}]

But if you do not want to access Rest API remotely then you do not need to enable TCP. Then you can just use unix socket.

List containers that are running same like docker ps

$ curl --unix-socket /var/run/docker.sock http:/v1.24/containers/json
[{
  "Id":"ae63e8b89a26f01f6b4b2c9a7817c31a1b6196acf560f66586fbc8809ffcd772",
  "Names":["/tender_wing"],
  "Image":"bfirsh/reticulate-splines",
  ...
}]

You can use Python and Go as well here is the Example:

Python

import docker
client = docker.from_env()
for container in client.containers.list():
  print container.id

Go

package main

import (
    "os"

    "github.com/docker/docker/api/types"
    "github.com/docker/docker/api/types/container"
    "github.com/docker/docker/pkg/stdcopy"
    "github.com/docker/docker/client"
    "golang.org/x/net/context"
)

func main() {
    ctx := context.Background()
    cli, err := client.NewClientWithOpts(client.FromEnv, client.WithAPIVersionNegotiation())
    if err != nil {
        panic(err)
    }

    reader, err := cli.ImagePull(ctx, "docker.io/library/alpine", types.ImagePullOptions{})
    if err != nil {
        panic(err)
    }
    io.Copy(os.Stdout, reader)

    resp, err := cli.ContainerCreate(ctx, &container.Config{
        Image: "alpine",
        Cmd:   []string{"echo", "hello world"},
        Tty:   true,
    }, nil, nil, "")
    if err != nil {
        panic(err)
    }

    if err := cli.ContainerStart(ctx, resp.ID, types.ContainerStartOptions{}); err != nil {
        panic(err)
    }

    statusCh, errCh := cli.ContainerWait(ctx, resp.ID, container.WaitConditionNotRunning)
    select {
    case err := <-errCh:
        if err != nil {
            panic(err)
        }
    case <-statusCh:
    }

    out, err := cli.ContainerLogs(ctx, resp.ID, types.ContainerLogsOptions{ShowStdout: true})
    if err != nil {
        panic(err)
    }

    stdcopy.StdCopy(os.Stdout, os.Stderr, out)
}

There are a number of libraries available for other languages.

Language	Library
C	libdocker
C#	Docker.DotNet
C++	lasote/docker_client
Dart	bwu_docker
Erlang	erldocker
Gradle	gradle-docker-plugin
Groovy	docker-client
Haskell	docker-hs
HTML (Web Components)	docker-elements
Java	docker-client
Java	docker-java
Java	docker-java-api
NodeJS	dockerode
NodeJS	harbor-master
Perl	Eixo::Docker
PHP	Docker-PHP
Ruby	docker-api
Rust	docker-rust
Rust	shiplift
Scala	tugboat
Scala	reactive-docker
Swift	docker-client-swift

Now you can create your own User Interface by using Docker Rest API. This API could help you in automating stuff for your Apps.