Nowadays everybody is talking about Docker. Some people are well versed with docker concepts and have hands on it and some have started learning docker.
So what is Docker?
As per the official docs from docker, Docker is a platform for developers and sysadmins to develop, deploy, and run applications with containers.
So what does make it different. We were already doing that since long.
So what does make it different. We were already doing that since long.
When we are deploying application on servers we have to deal with setting up new VM, configuring dependencies / libraries, environment variables. Docker makes this thing easy for you, by providing OS level virtualization (aka. containerization). So basically you can create Docker images that will have all your resources ( env. variables / libs / running on what port). Then you can deploy your application inside docker container anywhere without even worrying about the dependencies.
In traditional way you have to setup separate VM and then install all the required software and have all the dependencies in place , set the env variables. After doing all these sysadmin tasks then only you can deploy your application inside that VM.
Docker Architecture:
Installation details:
You can download docker community edition from docker - community-edition. Then install it as per the docker guide.
Docker Basic Commands:
- docker version: Used to check the docker version. (Client and server).
- docker info: Used to display system wide information. It includes kernel version, no of containers and images inside docker enviornment.
- docker run imagename: It first check whether your machine already have that docker image. If not found then it will download the same from docker repository and will run inside docker container.
- docker rmi imagename: To remove specific docker images from your machine. If your image has been used by any docker container (running instance of image) it will throw an error.
- docker inspect repositoryName: To get the detailed information about docker repository such as author of the repository, O.S, size, Config element if any.
C:\Users\DELL>docker version Client: Version: 17.12.0-ce API version: 1.35 Go version: go1.9.2 Git commit: c97c6d6 Built: Wed Dec 27 20:05:22 2017 OS/Arch: windows/amd64 Server: Engine: Version: 17.12.0-ce API version: 1.35 (minimum version 1.12) Go version: go1.9.2 Git commit: c97c6d6 Built: Wed Dec 27 20:12:29 2017 OS/Arch: linux/amd64 Experimental: true
C:\Users\DELL>docker info Containers: 9 Running: 4 Paused: 0 Stopped: 5 Images: 13 Server Version: 17.12.0-ce Storage Driver: overlay2 Backing Filesystem: extfs Supports d_type: true Native Overlay Diff: true Logging Driver: json-file Cgroup Driver: cgroupfs Plugins: Volume: local Network: bridge host ipvlan macvlan null overlay Log: awslogs fluentd gcplogs gelf journald json-file logentries splunk syslog Swarm: inactive Runtimes: runc Default Runtime: runc Init Binary: docker-init containerd version: 89623f28b87a6004d4b785663257362d1658a729 runc version: b2567b37d7b75eb4cf325b77297b140ea686ce8f init version: 949e6fa Security Options: seccomp Profile: default Kernel Version: 4.9.60-linuxkit-aufs Operating System: Docker for Windows OSType: linux Architecture: x86_64 CPUs: 2 Total Memory: 1.934GiB Name: linuxkit-00155d123c0b ID: BHUM:UVFR:XJUC:G7LT:Y2CX:76UL:JUBA:Q67S:2T4W:SQ6M:CLCR:NOX3 Docker Root Dir: /var/lib/docker Debug Mode (client): false Debug Mode (server): true File Descriptors: 36 Goroutines: 66 System Time: 2018-03-19T11:14:08.4256156Z EventsListeners: 1 Registry: https://index.docker.io/v1/ Labels: Experimental: true Insecure Registries: 127.0.0.0/8 Live Restore Enabled: false
C:\Users\DELL>docker run hello-world
Unable to find image 'hello-world:latest' locally
latest: Pulling from library/hello-world
ca4f61b1923c: Pull complete
Digest: sha256:97ce6fa4b6cdc0790cda65fe7290b74cfebd9fa0c9b8c38e979330d547d22ce1
Status: Downloaded newer image for hello-world:latest
Hello from Docker!
This message shows that your installation appears to be working correctly.
To generate this message, Docker took the following steps:
1. The Docker client contacted the Docker daemon.
2. The Docker daemon pulled the "hello-world" image from the Docker Hub.
(amd64)
3. The Docker daemon created a new container from that image which runs the
executable that produces the output you are currently reading.
4. The Docker daemon streamed that output to the Docker client, which sent it
to your terminal.
To try something more ambitious, you can run an Ubuntu container with:
$ docker run -it ubuntu bash
Share images, automate workflows, and more with a free Docker ID:
https://cloud.docker.com/
For more examples and ideas, visit:
https://docs.docker.com/engine/userguide/
C:\Users\DELL>docker rmi hello-world Error response from daemon: conflict: unable to remove repository reference "hello-world" (must force) - container f643045cfa75 is using its referenced image f2a91732366c // To check all the containers C:\Users\DELL>docker ps -a CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES f643045cfa75 hello-world "/hello" 5 minutes ago Exited (0) 5 minutes ago awesome_khorana // To forcefully remove the image C:\Users\DELL>docker rmi -f hello-world Untagged: hello-world:latest Untagged: hello-world@sha256:97ce6fa4b6cdc0790cda65fe7290b74cfebd9fa0c9b8c38e979330d547d22ce1 Deleted: sha256:f2a91732366c0332ccd7afd2a5c4ff2b9af81f549370f7a19acd460f87686bc7
C:\Users\DELL>docker inspect hello-world
[
{
"Id": "sha256:f2a91732366c0332ccd7afd2a5c4ff2b9af81f549370f7a19acd460f87686bc7",
"RepoTags": [
"hello-world:latest"
],
"RepoDigests": [
"hello-world@sha256:97ce6fa4b6cdc0790cda65fe7290b74cfebd9fa0c9b8c38e979330d547d22ce1"
],
"Parent": "",
"Comment": "",
"Created": "2017-11-21T00:23:18.797567713Z",
"Container": "fb0b4536aac3a96065e1bedb2b637a6019feec666c7699592206956c9d3adf5f",
"ContainerConfig": {
"Hostname": "fb0b4536aac3",
"Domainname": "",
"User": "",
"AttachStdin": false,
"AttachStdout": false,
"AttachStderr": false,
"Tty": false,
"OpenStdin": false,
"StdinOnce": false,
"Env": [
"PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin"
],
"Cmd": [
"/bin/sh",
"-c",
"#(nop) ",
"CMD [\"/hello\"]"
],
"ArgsEscaped": true,
"Image": "sha256:2243ee460b69c4c036bc0e42a48eaa59e82fc7737f7c9bd2714f669ef1f8370f",
"Volumes": null,
"WorkingDir": "",
"Entrypoint": null,
"OnBuild": null,
"Labels": {}
},
"DockerVersion": "17.06.2-ce",
"Author": "",
"Config": {
"Hostname": "",
"Domainname": "",
"User": "",
"AttachStdin": false,
"AttachStdout": false,
"AttachStderr": false,
"Tty": false,
"OpenStdin": false,
"StdinOnce": false,
"Env": [
"PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin"
],
"Cmd": [
"/hello"
],
"ArgsEscaped": true,
"Image": "sha256:2243ee460b69c4c036bc0e42a48eaa59e82fc7737f7c9bd2714f669ef1f8370f",
"Volumes": null,
"WorkingDir": "",
"Entrypoint": null,
"OnBuild": null,
"Labels": null
},
"Architecture": "amd64",
"Os": "linux",
"Size": 1848,
"VirtualSize": 1848,
"GraphDriver": {
"Data": {
"MergedDir": "/var/lib/docker/overlay2/61badba77bc2c48ceb5aefd993a293f1335c962a976c600b8c42dbcb513140fe/merged",
"UpperDir": "/var/lib/docker/overlay2/61badba77bc2c48ceb5aefd993a293f1335c962a976c600b8c42dbcb513140fe/diff",
"WorkDir": "/var/lib/docker/overlay2/61badba77bc2c48ceb5aefd993a293f1335c962a976c600b8c42dbcb513140fe/work"
},
"Name": "overlay2"
},
"RootFS": {
"Type": "layers",
"Layers": [
"sha256:f999ae22f308fea973e5a25b57699b5daf6b0f1150ac2a5c2ea9d7fecee50fdf"
]
},
"Metadata": {
"LastTagTime": "0001-01-01T00:00:00Z"
}
}
]
In this post we have seen the basic understanding of docker container and concepts around docker ecosystem. We have also seen docker basic commands. In the next post we will touch different features and the commands of working with docker container.