Docker Basics

Docker

https://docs.docker.com/engine/install/

## help message for docker
docker help

## help message for docker command
docker <sub-command> --help

Basic Concepts

Image

Images are template that we can use to run for different tasks. Docker.io supplies us many base images.

Related Commands

## display all images in current docker
docker images

## run as images
docker run <image id/name> <command>

## delete an image
docker rmi <image id/name>

## shortcut for run a temporary image to debug.
docker run --rm -it <image id/name> /bin/bash
docker run --rm -it <image id/name> /bin/sh    # for images without bash

Container

Container is a running task on docker. It uses an image as template. We can save changes maked on containers as a new image.

Related commands

## display all running containers
docker ps

## display all containers (including stopped)
docker ps -a

## start a stopped container
docker stop <container id/name>

## execute command in a container
docker exec <container id/name> <command>

## shortcut to go into the container
docker exec -it <container id/name> /bin/bash
docker exec -it <container id/name> /bin/sh    # for container without /bin/bash 

## commit a container as an image
docker commit <container id/name> <image name>[:<tag>]

Registry

Therea are many bas images supplied by docker.io like ubuntu, centos and so on. And we can set up a registry of ourselves.

Related commands

## get image from registry
docker pull <image name>

## push image to registry
docker push <image name>

Dockerfile

Docker can build images automatically by reading the instructions from a Dockerfile. A Dockerfile is a text document that contains all the commands a user could call on the command line to assemble an image. Using docker build users can create an automated build that executes several command-line instructions in succession.

Dockerfile Components:

Command	Description
FROM	for base image, this command must be on the top of the dockerfile
RUN	to execute commands, it will create a layer in image
MAINTAINER	author/owner/description
COPY	copy files from local system(docker vm) we need to provide source, destination(we can't download file from internet and any remote repo.)
ADD	similar to copy but it provides a feature to download files from internet, also extract file at docker image side.
EXPOSE	to expose ports sucha as port 8080 for tomcat, port 80 for nginx etc.
CMD	execute commands but during container creation
ENTRYPOINT	similar to CMD but has higher priority over CMD , first ccommand will be executed by ENTRYPOINT only
ENV	environment variables
WORKDIR	The WORKDIR command is used to define the working directory of a Docker container at any given time.
	Any RUN, CMD, ADD, COPY, or ENTRYPOINT command will be executed in the specified working directory. e.g. WORKDIR /directory

Steps:

Dockefile --> Instructions --> Build --> Run

1. Create a file named Dockerfile.
2. Add instructions in Dockerfile.
3. Build dockerfile to create image.
4. Run image to create container.

Docker - Essential Commands

Commands	Description
docker ps	List all running containers
docker ps -a	List all containers stopped, running
docker stop container-id	Stop the container which is running
docker start container-id	Start the container which is stopped
docker restart container-id	Restart the container which is running
docker port container-id	List port mappings of a specific container
docker rm container-id or name	Remove the stopped container
docker rm -f container-id or name	Remove the running container forcefully
docker pull image-info	Pull the image from docker hub repository
docker pull /	Pull the image from docker hub repository
docker exec -it container-name /bin/sh	Connect to linux container and execute commands in container
docker rmi image-id	Remove the docker image
docker logout	Logout from docker hub
docker login -u username -p password	Login to docker hub
docker stats	Display a live stream of container(s) resource usage statistics
docker top container-id or name	Display the running processes of a container
docker version	Show the Docker version information