Docker day 1

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Build, swap and remove infrastructure in a text file

Docker containers are a set of tools to quickly and easily build, swap out and remove infrastructure layers. You get 3 for one, on one hand you learn bash and containers while streamlining your workflow.

Under the hood Docker is a toolkit for two very old Linux features that are used to compartmentalize processes:  

• cgroups and
• namespaces.

Docker makes these otherwise arcane features much easier to use.

Main benefits

... of Containers include their reproducibility, portability and lightweightness.

• Reproducibility - Getting a service to a certain state and distributing that application to its users is one of the primary concerns for any system administrator. Containers are written in code using a layered approach and forces the administrator to codify their environments. You are introduced to the world of Infrastructure-as-code (IAAS) were servers are created, updated and destroyed in a text file.
• Portability is concerned with easily moving resources between servers/nodes in the network and being able to work with containers cross-platform or cross-cloud. When acquisitions happen (such as akami buying linode) the portability of "infrastructure as a code"-workflow enables much quicker deployment onto a new cloud platform.
• The smallest containers need only a few megabytes at most, start up in seconds and runs as one process, something that makes them very lightweight with a small foot print compared to traditional Virtual Machines that that can easily become gigabytes large and takes minutes to start.

Other benefits include

• A growing ecosystem of 'pre made' service definitions by the community
• Interoperability between major container platforms: Docker, Kubernetes and Podman. "create once bring the container everywere".

Image Creation like lego bricks

Image creation starts in text file by importing a 'base image' to work on and adding customization ontop of, very much like lego bricks. Everything written in the text file is parsed and converted into an image by the container platform. The image is like a compiled binary of your source code which can be distributed around your servers/nodes. Containers are run as defined in the text.

Important day 1 stuff

Dockerfiles build docker images which run docker containers.

• Dockerfile = text based instructions for docker to build/assemble an image. Keywords such as RUN, COPY, MOVE dicatate the location and startup of files and processes inside the image. Each "keyword/action" creates a layer in the docker image. Dockerfiles are read by the docker process from top to bottom.
• Docker image = read only archive containing executable files built from the dockerfile.
• Docker container = A running version of a docker image, loaded into memory

Dockerfiles often contain references to other docker images to simplify containers. Instead of writing an operating system container such as debian one can simply reference the debian container as the base container and build upon it. Docker downloads docker images/files according to the dockerfile text specification.

Docker filesystem locations

Docker has its own root directory (simillar to httpd/apache) which can be viewed using the docker info command, the default location is /var/lib/docker/. Important sysadmin subfolders in the docker root directory include:

• Dockerfiles - Dockerfiles can be stored anywere on the system and parsed by docker.
• /var/lib/docker/images -  Images created by reading dockerfiles are stored here and can be listed using the command docker images ls --all.
• /var/lib/docker/containers - Docker container location, list all containers using the command docker container ls --all
• /var/lib/docker/volumes - Persistent files are stored in either docker volumes subfolder or using bind mounts on the host system.

Use the command docker info for a quick overview of your installation.

Persistance vs ephemeral storage

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this section will be updated ..

Resources

Were did my init system go?

How do filesystems work in containers?

The container lifecycle

Build containers

Manage networks

Manage volumes

Resource

Read this:

Best practices for writing Dockerfiles

Hints, tips and guidelines for writing clean, reliable Dockerfiles

Docker Documentation

The MariaDB knowledgebase has some great writeups about docker.

Installing and Using MariaDB via Docker

Creating and managing a MariaDB Docker container.

MariaDB KnowledgeBase

The container lifecycle

Push/Pull, Create from image, list containers, Run/Stop, Persistent storage, Replace, Delete.

Environment variables

Secrets

Stuff we want to do

List all containers

List all running containers

List all images (that create containers)

Link containers together (create a shared network, linking is deprecated)

docker network create fivenet --driver bridge --subnet 10.13.37.1/24

docker network ls # confirm network created

docker container run --name maria --hostname maria --network fivenet -e MARIADB_ROOT_PASSWORD=password mariadb

docker container run --name phpmyadmin --hostname phpmyadmin --network fivenet

Download an image

Create a container

docker container create --help 
$ docker container create --help
Usage:  docker container create [OPTIONS] IMAGE [COMMAND] [ARG...]
.....

docker container create --name [name] [image]

Start a container

Example 1, starting phpmyadmin

NOTE THIS VERSION HAS NO DATA PERSITANCE BETWEEN CONTAINER "reboots"

docker pull mariadb

docker pull phymyadmin

docker container run --name maria --hostname maria --network fivenet -e MARIADB_USER=admin -e MARIADB_PASSWORD=admin -e MARIADB_ROOT_PASSWORD=root mariadb

docker run -dit --name myadmin --hostname myadmin --network fivenet -p 5555:80 -e PMA_HOST=maria -e PMA_PORT=3306 -e PMA_USER=root -e PMA_PASSWORD=root phpmyadmin

go into a container

docker exec -it <container name> /bin/bash  

Creating a compose script

Compose can reduce a multi-page “developer getting started guide” to a single machine readable Compose file and a few commands.