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diff --git a/docker.html.markdown b/docker.html.markdown new file mode 100644 index 00000000..ec6abe7e --- /dev/null +++ b/docker.html.markdown @@ -0,0 +1,281 @@ +--- +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 publicly 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` + +``` |