mirror of
https://github.com/adambard/learnxinyminutes-docs.git
synced 2024-11-25 20:14:30 +03:00
282 lines
15 KiB
Markdown
282 lines
15 KiB
Markdown
---
|
|
category: tool
|
|
tool: docker
|
|
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"]
|
|
---
|
|
|
|
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/
|
|
|
|
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.
|
|
|
|
<pre>
|
|
┌────────────────────────┐ ┌───────────────────────┐
|
|
│ ┌───────────┐ │ │ ┌───────────┐ │
|
|
│ │ App │ │ │ │ App │ │
|
|
│ └───────────┘ │ │ └───────────┘ │
|
|
│ ┌────────┐ ┌────────┐ │ │ ┌────────┐ ┌───────┐ │
|
|
│ │ Libs │ │ Deps │ │ │ │ Libs │ │ Deps │ │
|
|
│ └────────┘ └────────┘ │ │ └────────┘ └───────┘ │
|
|
│ ┌───────────────────┐ │ │ ┌──────────────────┐ │
|
|
│ │ Guest OS │ │ │ │ Guest OS │ │
|
|
│ └───────────────────┘ │ │ └──────────────────┘ │
|
|
│ VM1 │ │ VM2 │
|
|
└────────────────────────┘ └───────────────────────┘
|
|
┌──────────────────────────────────────────────────┐
|
|
│ Hypervisor │
|
|
└──────────────────────────────────────────────────┘
|
|
┌──────────────────────────────────────────────────┐
|
|
│ Host OS │
|
|
└──────────────────────────────────────────────────┘
|
|
┌──────────────────────────────────────────────────┐
|
|
│ Hardware Infrastructure │
|
|
└──────────────────────────────────────────────────┘
|
|
(VM based architecture)
|
|
|
|
┌────────────────────────┐ ┌───────────────────────┐
|
|
│ ┌───────────┐ │ │ ┌───────────┐ │
|
|
│ │ App │ │ │ │ App │ │
|
|
│ └───────────┘ │ │ └───────────┘ │
|
|
│ ┌────────┐ ┌────────┐ │ │ ┌────────┐ ┌───────┐ │
|
|
│ │ Libs │ │ Deps │ │ │ │ Libs │ │ Deps │ │
|
|
│ └────────┘ └────────┘ │ │ └────────┘ └───────┘ │
|
|
│ Container1 │ │ Container2 │
|
|
└────────────────────────┘ └───────────────────────┘
|
|
┌──────────────────────────────────────────────────┐
|
|
│ Docker │
|
|
└──────────────────────────────────────────────────┘
|
|
┌──────────────────────────────────────────────────┐
|
|
│ OS │
|
|
└──────────────────────────────────────────────────┘
|
|
┌──────────────────────────────────────────────────┐
|
|
│ Hardware Infrastructure │
|
|
└──────────────────────────────────────────────────┘
|
|
(Docker based architecture)
|
|
|
|
</pre>
|
|
|
|
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.
|
|
|
|
## 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
|
|
|
|
>>> docker [OPTIONS] COMMAND [ARG...]
|
|
docker [ --help | -v | --version ]
|
|
|
|
A self-sufficient runtime for containers.
|
|
|
|
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
|
|
|
|
Commands:
|
|
attach Attach to a running container
|
|
# […]
|
|
|
|
$ 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 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
|
|
|
|
$ 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 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
|
|
# 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`
|
|
|
|
```
|