Docker

Makes running apps in containers easy.

Also, Docker Inc:

• Technology start-up from San Francisco.
• Main sponsor of the open-source technology with the same name.
• Originally dotCloud — provided a developer platform on top of AWS — Used containers for this.
• Homegrown tech which they built as an internal tool to run and manage their containers ⇒ Docker
• Now they sell enterprise-grade container management and providing support

To check for what version of docker is installed or if you have docker installed at all in you system -

docker version

Docker variants

• Docker Community Edition (CE)
• Open source — Lives on Github
  • Quick release cycle
  • Contributions and support from large organisations like IBM, Red Hat, Microsoft etc.
• Docker Enterprise Edition (EE)
  • Sold by Docker Inc.
  • Extra features
  • Official support
  • Slower release cycle
• Play with Docker
  • From Docker Inc.
  • Time limit of 4 hours
  • Provides fully working docker instance

Features

• Docker is language agnostic.
• In the container, the application automatically binds to the port on which it runs

Dockerfile

Set of build instructions — set of steps for Docker to follow to build the app and its dependencies into a container image.

Managing Container Images in Docker

Building an image

docker image build -t yourDockerHubID/repoName:imageName

Hosting image on Container Registry

docker image push yourDockerHubID/repoName:imageName

Listing local images

docker image ls

Managing Containerized Apps in Docker

Running a containerized app

docker container run -d --name containerName -p 8000:8080 \

>DockerHubID/repoName:imageName

Flags:

• -d (detached): to run the container in the background detached from the terminal
• --name : to specify the container name
• -p : for Port Mapping or Forwarding — any request to port 8000 on your system/remote server will redirect to port 8080 of the container - where the app is running.
• -it (interactive terminal): to run the container in foreground attached to the terminal
  • In this mode, you can run any command in your terminal and it will actually get executed on the container. You will be basically be inside the container on your terminal.
  • You can come out of it using exit command. Although, this will also kill the container, as you are effectively killing the shell process that was the main process of the container.
  • Leaving the container without terminating it: Ctrl + P + Q

How docker gets the image

• Docker first checks locally for the container image. If it doesn’t exist, then it goes to the Docker hub
• If you want to run image from a different registry, you need to enter the URL of the image.

Running

• On local system — localhost:8000
• On cloud system — DNS/public IP of the cloud instance:8000

Managing a containerized app

Stopping the app

docker container stop containerName

Docker sends the app a SIGTERM signal and waits for a few seconds for it to shut down gracefully. If it doesn’t, its terminated with a SIGKILL

Starting the app

docker container start containerName

Removing the app

docker container rm containerName

Removing the app forcefully -f flag

Listing containers

Listing running containers:

docker container ls

Listing all images/containers Use a -a flag along with the command.