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GitOps with Argo CD

The cluster as a copy of a Git repository: sync, drift and rollback.

An interactive Kubernetes lesson: 21 steps, about 30 minutes, on a live simulation in your browser.

You run the shop's website. Three copies of web serve customers through a NodePort Service on port 30080. Every deploy is someone on the team running helm install or helm upgrade from their laptop, with a values file that lives on the same laptop.

It works. Customer requests flow and every one returns 200. Watch that traffic line as the lesson goes on: it stays green through most of what follows, which is exactly why the problems ahead go unnoticed for so long.

What you will learn

  1. Deploys by hand

    • The shop runs on hand applies: A hand deploy sends files to the cluster. Nothing records which files, from whose laptop, or in which order.
    • Two laptops, two truths: If the values are not in git, the release cannot be rebuilt from scratch. The laptop is a single point of failure.
    • A hotfix at midnight: Live edits fix the cluster and leave the repo behind. From that moment the two disagree.

  2. Drift

    • Argo CD moves in: GitOps means the repo is the desired state and the cluster is measured against it. Drift is any difference between the two.
    • Break it: five where git says three
    • Nobody presses sync
    • Read the diff before the sync

  3. The Application object

    • One object points at git: An Application says: this repo, this revision, this cluster. Everything Argo CD does follows from those three lines.
    • What a branch revision follows: targetRevision picks the commit. A branch follows movement; a tag or SHA pins one commit.
    • Press sync: A sync writes git onto the cluster. Live edits are overwritten, never merged.

  4. Drift correction

    • Three switches: auto, prune, heal: Automated sync closes the loop. Prune deletes what git removed. SelfHeal reverts what hands changed.
    • Break it: down to one by hand
    • SelfHeal notices: SelfHeal makes live edits temporary. The cluster converges back to git on its own.
    • Prune deletes the stray: Prune deletes what git stopped asking for. It never touches what git never owned.
    • Drill: sync one app by hand

  5. Rollback with Git and Helm

    • Break it: the tag that was never pushed
    • Revert the commit, not the cluster: Roll back the repo, not the cluster. The sync carries the fix wherever the app runs.
    • Git says why, Helm says what: Git is the intent: who meant what, and why. The release history is the fact: what the cluster actually ran.
    • Drill: read the release history

  6. Recap & playground

    • Cheat sheet
    • Playground