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Containers

Container Basics​

  • Containers are used to ensure that the application is always run with the same asumptions.
  • Whether in development or production, containers ensure that the application always has the correct dependencies.
  • The most common tool to create containers is Docker.

Terminology​

  • Image: A package with the compiled app and dependencies.
  • Container: A running instance of a container image.
  • Dockerfile: The build instructions for creating an image.
  • Build: Creating an image from Dockerfile
  • Volumes: File systems that are made available to the container.
  • MSB: Multi-stated Build
  • Registry: A place to store container images
  • Docker Compose: A tool to run multiple container images together

Dockerfiles​

  • In order to create containers with Docker, we must create an image.
  • Images are created from Dockerfiles. A Dockerfile must have a base image and probably does several steps to set up the enviornment for the new images.
  • The docker build command is used to build images from docker files.
  • Then the images can be run, which turns them into containers.

Multi-stage Builds​

  • Sometimes, it is ideal to have a one environment for building the source or for some other action, and another for running it in production.
  • One soltuion to this would be to have two different dockerfiles along with a shell script to manage them, but this is complex and leads to large container sizes
  • Instead, multi-stage builds can be added to the docker file to seperate various stages of the development and deployment process.

Running Containers​

  • Containers can be started with docker run [options] [container].
  • They can be stopped with docker stop [container].

Docker Compose​

  • Docker compose is used to orchestrate the running of several different containers for a singular project
  • Various configurations can be passed into the docker-compose.yml, so that command line arguments do not need to be used everytime a container needs to be started.
  • The containers can be started with docker compose up and closed with docker compose down.