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Merge pull request #4541 from akshitadixit/docker-docs

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[docker/en] Rewriting the docs for Docker
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Marcel Ribeiro Dantas
2022-11-27 16:11:11 -03:00
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@@ -5,144 +5,277 @@ filename: docker.bat
contributors:
- ["Ruslan López", "http://javapro.org/"]
- ["Michael Chen", "https://github.com/ML-Chen"]
- ["Akshita Dixit", "https://github.com/akshitadixit"]
- ["Marcel Ribeiro-Dantas", "https://github.com/mribeirodantas"]
---
```bat
:: download, install and run hello-world image
docker run hello-world
Docker is a tool that helps you build, test, ship and run applications
seamlessly across various machines. It replicates the environment our software
needs on any machine. You can get Docker for your machine from
https://docs.docker.com/get-docker/
:: if this is the first time you should be able to see the message
:: Unable to find image 'hello-world:latest' locally
:: latest: Pulling from library/hello-world
:: 1b930d010525: Pull complete
:: Digest: sha256:4fe721ccc2e8dc7362278a29dc660d833570ec2682f4e4194f4ee23e415e1064
:: 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://hub.docker.com/
::
:: For more examples and ideas, visit:
:: https://docs.docker.com/get-started/
It has grown in popularity over the last decade due to being lightweight and
fast as compared to virtual-machines that are bulky and slow. Unlike VMs, docker
does not need a full blown OS of its own to be loaded to start and does not
compete for resources other than what the application it is running will use.
VMs on the other hand are pretty resource intensive on our processors, disks and
memory hence running multiple VMs for various applications becomes a challenge
in a limited capacity architecture.
:: now let's see currently running images
docker ps
:: CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS
:: NAMES
<pre>
┌────────────────────────┐ ┌───────────────────────┐
│ ┌───────────┐ │ │ ┌───────────┐ │
│ │ App │ │ │ │ App │ │
│ └───────────┘ │ │ └───────────┘ │
│ ┌────────┐ ┌────────┐ │ │ ┌────────┐ ┌───────┐ │
│ │ Libs │ │ Deps │ │ │ │ Libs │ │ Deps │ │
│ └────────┘ └────────┘ │ │ └────────┘ └───────┘ │
│ ┌───────────────────┐ │ │ ┌──────────────────┐ │
│ │ Guest OS │ │ │ │ Guest OS │ │
│ └───────────────────┘ │ │ └──────────────────┘ │
│ VM1 │ │ VM2 │
└────────────────────────┘ └───────────────────────┘
┌──────────────────────────────────────────────────┐
│ Hypervisor │
└──────────────────────────────────────────────────┘
┌──────────────────────────────────────────────────┐
│ Host OS │
└──────────────────────────────────────────────────┘
┌──────────────────────────────────────────────────┐
│ Hardware Infrastructure │
└──────────────────────────────────────────────────┘
(VM based architecture)
:: let's see the images we have ran previously
docker ps -a
┌────────────────────────┐ ┌───────────────────────┐
│ ┌───────────┐ │ │ ┌───────────┐ │
│ │ App │ │ │ │ App │ │
│ └───────────┘ │ │ └───────────┘ │
│ ┌────────┐ ┌────────┐ │ │ ┌────────┐ ┌───────┐ │
│ │ Libs │ │ Deps │ │ │ │ Libs │ │ Deps │ │
│ └────────┘ └────────┘ │ │ └────────┘ └───────┘ │
│ Container1 │ │ Container2 │
└────────────────────────┘ └───────────────────────┘
┌──────────────────────────────────────────────────┐
│ Docker │
└──────────────────────────────────────────────────┘
┌──────────────────────────────────────────────────┐
│ OS │
└──────────────────────────────────────────────────┘
┌──────────────────────────────────────────────────┐
│ Hardware Infrastructure │
└──────────────────────────────────────────────────┘
(Docker based architecture)
:: CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS
:: NAMES
:: 4a76281f9c53 hello-world "/hello" 2 minutes ago Exited (0) 2 minutes ago
:: happy_poincare
:: the name part is generated automatically so it probably will be different for you
</pre>
:: let's remove our previously generated image
docker rm happy_poincare
Couple of terms we will encounter frequently are Docker Images and Docker
Containers. Images are packages or templates of containers all stored in a
container registry such as [Docker Hub](https://hub.docker.com/). Containers
are standalone, executable instances of these images which include code,
runtime, system tools, system libraries and settings - everything required to
get the software up and running. Coming to Docker, it follows a client-server
architecture wherein the CLI client communicates with the server component,
which here is, the Docker Engine using RESTful API to issue commands.
:: let's test if it was really deleted
docker ps -a
:: CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS
:: NAMES
## The Docker CLI
```bash
# after installing Docker from https://docs.docker.com/get-docker/
# To list available commands, either run `docker` with no parameters or execute
# `docker help`
$ docker
:: specify a custom name for the container
docker run --name test_container hello-world
:: 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://hub.docker.com/
::
:: For more examples and ideas, visit:
:: https://docs.docker.com/get-started/
>>> docker [OPTIONS] COMMAND [ARG...]
docker [ --help | -v | --version ]
docker ps -a
:: CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS
:: NAMES
:: d345fe1a4f41 hello-world "/hello" About a minute ago Exited (0) About a minute ago
:: test_container
:: as you can see the name is now what we have specified
A self-sufficient runtime for containers.
:: retrieve logs from a named container
docker logs test_container
:: 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://hub.docker.com/
::
:: For more examples and ideas, visit:
:: https://docs.docker.com/get-started/
Options:
--config string Location of client config files (default "/root/.docker")
-c, --context string Name of the context to use to connect to the daemon (overrides DOCKER_HOST env var and default context set with "docker context use")
-D, --debug Enable debug mode
--help Print usage
-H, --host value Daemon socket(s) to connect to (default [])
-l, --log-level string Set the logging level ("debug"|"info"|"warn"|"error"|"fatal") (default "info")
--tls Use TLS; implied by --tlsverify
--tlscacert string Trust certs signed only by this CA (default "/root/.docker/ca.pem")
--tlscert string Path to TLS certificate file (default "/root/.docker/cert.pem")
--tlskey string Path to TLS key file (default "/root/.docker/key.pem")
--tlsverify Use TLS and verify the remote
-v, --version Print version information and quit
docker rm test_container
Commands:
attach Attach to a running container
# […]
docker run ubuntu
:: Unable to find image 'ubuntu:latest' locally
:: latest: Pulling from library/ubuntu
:: 2746a4a261c9: Pull complete
:: 4c1d20cdee96: Pull complete 0d3160e1d0de: Pull complete c8e37668deea: Pull complete Digest: sha256:250cc6f3f3ffc5cdaa9d8f4946ac79821aafb4d3afc93928f0de9336eba21aa4
:: Status: Downloaded newer image for ubuntu:latest
$ docker run hello-world
# `docker run <container-name>` is used to run a container, it will pull the
# images from Docker Hub if they don't already exist in your system. Here the
# docker client connects to the daemon which in turn pulls the "hello-world"
# image from the Docker Hub. The daemon then builds a new container from the
# image which runs the executable that produces the output streamed back to the
# client that we see on our terminals.
docker ps -a
:: CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS
:: NAMES
:: c19e9e5b000a ubuntu "/bin/bash" 5 seconds ago Exited (0) 4 seconds ago
:: relaxed_nobel
$ docker run -d ubuntu sleep 60s
# The -d (or --detach) flag is when we want to run a container in the background
# and return back to the terminal. Here we detach an ubuntu container from the
# terminal, the output should be the id and the command exits. If we check
# running containers, we should still see ours there:
# CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
# 133261b4894a ubuntu "sleep 60s" 3 seconds ago Up 2 seconds vigorous_gould
:: running a container in an interactive mode
docker run -it ubuntu
:: root@e2cac48323d2:/# uname
:: Linux
:: root@e2cac48323d2:/# exit
:: exit
$ docker run <container-id> -p 3000:8000
# The -p (or --publish) flag is used to expose port 8000 inside the container to
# port 3000 outside the container. This is because the app inside the container
# runs in isolation, hence the port 8000 where the app runs is private to the
# container.
docker rm relaxed_nobel
$ docker run -i
# or
$ docker run -it
# Docker runs our containers in a non-interactive mode i.e. they do not accept
# inputs or work dynamically while running. The -i flag keeps input open to the
# container, and the -t flag creates a pseudo-terminal that the shell can attach
# to (can be combined as -it)
docker ps -a
:: CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS
:: NAMES
:: e2cac48323d2 ubuntu "/bin/bash" 2 minutes ago Exited (0) About a minute ago
:: nifty_goldwasser
$ docker ps -a
# The `docker ps` command only shows running containers by default. To see all
# containers, use the -a (or --all) flag
# Running the above command should output something similar in the terminal:
# CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
# 82f84bf6912b hello-world "/hello" 9 minutes ago Exited (0) 9 minutes ago eloquent_sammet
$ docker stop hello-world
# or
$ docker start hello-world
# The stop command simply stops one or more containers, and the start command
# starts the container(s) up again! `docker start -a ubuntu` will attach our
# detached container back to the terminal i.e. runs in the foreground
$ docker create alpine
# `docker create` creates a new container for us with the image specified (here,
# alpine), the container does not auto-start unlike `docker run`. This command
# is used to set up a container configuration and then `docker start` to shoot
# it up when required. Note that the status is "Created":
# CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
# 4c71c727c73d alpine "/bin/sh" 29 seconds ago Created naughty_ritchie
$ docker rm 82f84
# Removes one or more containers using their container ID.
# P.S.: we can use only the first few characters of the entire ID to identify
# containers
$ docker images
# Displays all images and their information, created here means the latest image
# tag updated on Docker Hub:
# REPOSITORY TAG IMAGE ID CREATED SIZE
# ubuntu latest a8780b506fa4 9 days ago 77.8MB
# alpine latest 9c6f07244728 3 months ago 5.54MB
# hello-world latest feb5d9fea6a5 13 months ago 13.3kB
$ docker rmi
# Removes one or more images from your system which do not have their instances
# (or containers as we know them) running. If the image has an attached
# container, either delete the container first or use the -f (or --force) flag
# to forcefully delete both the container and image.
$ docker pull busybox
# The pull command downloads the specified image on our system from Docker Hub.
$ docker exec -it 7b272 bash
# This command is used to run a command in the running container's default
# directory. Here 7b272 was our ubuntu container and the above command would
# help us interact with the container by opening a bash session.
$docker logs <container-id>
# Displays the information logged by the specified container
# root@7b27222e4bb7:/# whoami
# root
# root@7b27222e4bb7:/# pwd
# /
# root@7b27222e4bb7:/# ls
# bin boot dev etc home lib lib32 lib64 libx3 srv sys tmp usr var
# root@7b27222e4bb7:/# exit
# exit
# More commands can be found at https://docs.docker.com/engine/reference/commandline/docker/
```
## The Dockerfile
The Dockerfile is a blueprint of a Docker image. We can mention the artifacts
from our application along with their configurations into this file in the
specific syntax to let anyone create a Docker image of our application.
### A few things to keep in mind:
* It is always strictly named `Dockerfile` without any extensions
* We have to build our custom image on top of some already available Docker base
image. (there is an empty image called `scratch` which literally lets you build
an image from scratch)
* All capitalised commands are part of the syntax, they are not case-sensitive
but used like a convention
* Below is a sample Dockerfile but you can read in depth from the [official docs](https://docs.docker.com/engine/reference/builder/).
```Dockerfile
FROM <base-image>
# define base image
ENV USERNAME='admin'\
PWD='****'
# optionally define environmental variables
RUN apt-get update
# run linux commands inside container env, does not affect host env
# This executes during the time of image creation
COPY <src> <target>
# executes on the host, copies files from src (usually on the host) to target
# on the container
ENTRYPOINT ["some-script.sh"]
# executes an entire script as an entrypoint
CMD [<args>,...]
# always part of dockerfile, introduces entry point linux command e.g.
# `CMD node server.js`
# This executes after image creation only when the container from the image
# is running.
```
### Build your images
Use the `docker build` command after wrapping your application into a Docker
image to run ( or build) it.
```bash
$docker build <path-to-dockerfile>
# used to build an image from the specified Dockerfile
# instead of path we could also specify a URL
# -t tag is optional and used to name and tag your images for e.g.
# `$docker build -t my-image:0.1 ./home/app`
# rebuild images everytime you make changes in the dockerfile
```
## Push your image to DockerHub
If you want your application's Docker image to be made publically available for
any Docker user, you might wanna push it to the [Docker Hub](https://hub.docker.com/) which is a
registry of Docker images. Make sure you have an account with a username and
password on Docker Hub.
When pushing an image to Docker Hub, we must specify our Docker Hub username
as part of the source image name. We need to create the target image with the
tag name of username/image-name much like GitHub repositories.
```bash
$docker login
# to login to Docker Hub using your username and password
$docker tag <src-image>[:<src-tag>] <target-image>[:<target-tag>]
# this tags a local src-image to a public target-image
# e.g. `docker tag my-sample-app:1.0.0 akshitadixit/my-sample-app`
# if tags are not specified, they're defaulted to `latest`
$docker push <target-image>[:<target-tag>]
# uploads our image to Docker Hub
# e.g. `docker push akshitadixit/my-sample-app`
# this image will be accessible under your profile's repositories as
# `https://hub.docker.com/r/username/image-name`
docker rm nifty_goldwasser
```