Dmitrii Abramov
Dmitrii Abramov Passionate Software Developer

Quick guide to Docker

Quick guide to Docker

This is a quick introduction to the basic Docker capabilities that might be useful for the most of developers for everyday use.

Intro

Docker is a powerful tool for creating containers (lightweight virtual machines, that use kernel of host OS as their kernel).

Basics

Docker image - is configured image of the container. Docker container is an instance of Docker image.

Creating an image

To create a Docker container you should either:

  • pull it from Docker Hub.
  • or create it using docker build command.

To see all images available locally you should issue docker images command.

Pulling an image

Use docker pull [image_name]:[tag] command to fetch an image from Docker Hub.

Tag is used for certain version of an image. By default it’s latest.

Running a container

To run a Docker container you should use docker run [instance] command. It has a lot of flags. The most useful are:

  • -d will run container in the background.
  • --name [name] will create the container with certain name.

  • -p [host_port]:[container_port] will expose container’s ports to host ports.

    For example:
    docker run -d -p 8080:8080 jenkins

  • -e [VARNAME]=[variable_value] will set environmental variable inside the container.

    For example:
    docker run -d --name mysql -e MYSQL_ROOT_PASSWORD=root -p 3306:3306 mysql:5.7

  • -v [your_data_directory]:[directory_inside_container] will mount a volume for directory in your container.

    It means that any data in this directory will be kept across container restarts (without volume, it won’t). For example:
    docker run -v your_data_directory:/var/data/elasticsearch elasticsearch.

    You also may use volumes to provide configuration files like this (:ro means that access to volume is read-only):
    docker run -d -p 80:80 -v /some/nginx.conf:/etc/nginx/nginx.conf:ro nginx

Operating containers

To see the list of running containers you may issue docker ps command.
To see all containers available on the machine you should issue docker ps -a.

All following commands accept container ID (or even it’s prefix, for your convenience):

  • docker start [id] - run existing container.
  • docker pause [id] - pause all processes inside the container.
  • docker stop [id] - stop a running container.
  • docker exec [id] [command] - execute command in container.

To remove image or container you may use:

  • docker rm [id] - remove container.
  • docker rmi [image_id] - remove image.

To interact with your container withought SSH configured, you may use docker exec -it to run bash command inside the container in interactive mode:

docker exec -it [container_name] /bin/bash

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