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I. What is Docker? - Definitions

  • In a Nutshell, Docker is an ecosystem for packaging a web app and its host environment into a consumer-ready deliverable.
  • Is a containerization (not virtualization) platform.
    • Is NOT the hypervisor.
    • This makes it lightweight enough to run on any OS that supports Docker (More on this in the Scalability section.)

So why should I care about Docker? Isn't it only for Linux developers? The fact is, with the advent of WSL, and especially since the release of WSL 2, Docker is becoming more and more accessible to Windows developers too.

II. Some advantages of the Docker ecosystem:

  • Light-weight Compartmentalization with external visibility

    • Forces sysadmins to properly deal with the separation of data from the app (backups).
    • Exploits in your app (or a sibling container) won't take down the host.
    • Unlike a full virtualization platform, you can still see into the container images from the host.

  • Cross-platform compatibility

    • Because they include the OS, they can be deployed on a totally dissimilar system from your dev environment - even with non-cross-platform apps. (Norman will describe how to consume a Docker image in his part of this talk.)
    • Docker can run on any hardware from ARM 64 platforms like the Raspberry Pi to cloud clusters, enabling painless migration to other OS's.
      • Give yourself an out when your host OS is discontinued. (Running on CentOS vs Docker within CentOS)
      • Protect yourself against vendor lock-in. (Contractual difficulties with cloud hosting providers - Parler app).

  • Security

    • In the hands of the image publisher. You select the OS environment for your app.
    • You update when you want to, after careful testing. The burden of ensuring compatibility between the App, its Dependencies, and the OS is now on the Developers rather than the unsuspecting Sysadmin. Remove the 'Oh, no!' moments when an OS update breaks live systems on the field.
    • Use docker scan to check your local images.

  • Scalability

    • Docker has become the linga franca of containerization.
    • Manage your containers directly with Docker Swarm or Kubernetes, with Portainer, or with cloud ecosystems like OpenStack, MS Azure, or AWS.
    • Some of these cloud services directly integrate with Docker.

III. Some specific use-cases for Docker:

  • Flexible development toolchains with image layers and snapshots (Gitea, Seq)
    • Share configuration among team members and customize from that.
  • "Throw-away" build environments (CI/CD pipelines)
  • Portable and scalable testing environments (NPM, Postman (newman)).
  • "One-click", pre-configured software installs.

IV. Basic Docker Components

Here's the high-level difference between docker commands, .dockerfile, and Docker Compose:

  • docker commands are for manually building images and running containers
  • .dockerfile is the script used to build docker images from the contents of a given directory.
  • .docker-compose.yml files are scripts that automate the tasks you can do manually with docker commands.
    • They're not a one-to-one correlation to docker commands.
    • Often used to manage clusters of dependent images. (The cloud platforms mentioned earlier would rely on Docker Compose.)

V. Build Demo (for the Devs)

Build the docker image via code (.dockerfile) I. Build on SG's dev PC

  • Simple docker build from existing binaries (used for CI pipelines)
  • The Build Context:
    • If you want the directory from which you call BUILD, use .
    • May be overriden with a local PATH or a Git URL
    • If dockerfile is not in this context, you must specify it with the '-f' flag.
      • Example: docker build -f scripts/dockerfile --force-rm -t abc21/update-server:test .
      • Note that we must use properly formed Linux paths (/, not \)
  • TODO: Port Bindings
  • TODO: Volume declaration
  • TODO: Environment variables
  • Spin up app.

II. Build from 'remote' Git repository

  • docker build with Git repo path
    • GitHub example: docker build -f scripts/dockerfile-build --force-rm -t abc21/update-server:latest github.com/ode2code95/ac21-update-server#develop
    • To run: docker run -d -p 5000:80 --name abc21-container-test abc21/update-server:latest
    • Note the branch-name notation.
  • Image will dotnet restore and build code.
  • Note: Be sure to clean up source when done.
  • Image will run resulting binaries

VI. Deployment Demo (for the SysAdmins)

By Norman King. Notes may be available later.