Docker

The Docker Lifecycle

• Starting the Service in Linux -> sudo service docker start
• Create Container -> docker create <imageName>
  • The docker client will search locally the image or it will reach the Docker hub to grab the image
• Start container -> docker start <id> <defaultCommand>
  • The filesystem of the image gets copy to the container allongside the default command
  • Once running the container, the default command cant be overrided
  • If you want to execute other commands you will have to use the exec command docker exec <containerId> <command>
  • You can read and enter text into the container with the -it flags docker exec -it <containerId> <command>
  • Many images have shells that you can run. To enter the filesystem with the shell use docker run -it <containerName> sh

You can make create and start the container at once with docker run <id> or <ImageName> <defaultCommand>

• Paused State
• Stop the Container
  • You can either send a SIGTERM signal with docker stop <id> to give it 10 seconds to gracefully shutdown
  • Or, you can send a SIGKILL with docker kill <containerId> to shutdown inmediatly

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Creating your own Images

You can use your own images by writting a Dockerfile

The docker Image can have:

1. A base Image using the commands FROM <baseImage> like FROM node:alpine
2. Specifying the proccess the container will execute RUN <command> like RUN npm install
3. Defining the post-command with CMD["string array"] like CMD ["npm","start"]

To make a container from your own custom image you will run docker build . where the . is the context.

You can copy local files to your docker container with the COPY command like COPY ./ ./ to copy the root directory to the container root directory

• If you want to copy anywhere else in the container you can use the WORKDIR command like WORKDIR '/app'

You can also tag your instances with docker build -t <yourName/nameOfContainer:version> . so you dont have to run the container with the id.

If you want to anyways run the the container using the id you can just copy a couple of first alphanumeric characters and Docker will identify wich id is the correct container

A container will have by default the output ports closed to the outside world (input ports are open by default) to map ports you can use docker run -p <localPortNumber>:<containerPortNumber> <imageName>

Running multiple containers that commnicate with eachother

You can use the Docker cli to handle multiple containers and make a network between your containers but this is pain in the ass. It is better to use a tool name Docker Compose

You will have to create a docker-compose.yml In it you will enter

1. The version like version: 3

2. The services (the container) services like

   1. redis-server:
      1. image: redis

3. You can set optional options like:

   Flag	command
   restart	always
   build	.
   ports	"4001:8080"

To create and run docker-compose up --

To rebuild the containers when you change your source files docker-compose up --build

To kill the containers docker-compose down

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Docker useful commands

• docker ps -> Look the active containers

• docker ps --all Look the running containers and the ones that are stopped.

• docker images -> Look to all the images you have downloaded

• docker rmi <IMAGEID> -> remove a docker image

• docker inspect <repository> -> Inspect a repository

• docker rm <ContainerId> -> Remove a Container

• docker run -d <containerId> -> Run withouts outputting the results

• docker system prune Remove all your images and erease the cache.

• docker logs <containerId> -> Watch all the output the container has generated

• docker image -q -> Get the id of and image

Terminology

Alpine : minimal

Links

• Docker Hub

• Great Docker and Kubernetes Course