95 lines
3.6 KiB
Markdown
95 lines
3.6 KiB
Markdown
 
|
# 06 — Your first change
|
||
|
|
|
||
|
|
Everything so far proved Argo CD can deploy what's in Git. This doc proves
|
||
|
|
the part that actually matters day to day: changing what's in Git and
|
||
|
|
watching the cluster follow, with no `kubectl apply` from you at all.
|
||
|
|
|
||
|
|
## Steps
|
||
|
|
|
||
|
|
1. Open [`apps/demo/configmap.yaml`](../apps/demo/configmap.yaml) and edit
|
||
|
|
the HTML — change the `<h1>` text to something of your own.
|
||
|
|
|
||
|
|
2. Commit and push, exactly like any other Git change:
|
||
|
|
```sh
|
||
|
|
git add apps/demo/configmap.yaml
|
||
|
|
git commit -m "Personalize the demo page"
|
||
|
|
git push
|
||
|
|
```
|
||
|
|
|
||
|
|
3. By default, Argo CD polls Git every three minutes, so your change will
|
||
|
|
show up on its own — but you can force it immediately:
|
||
|
|
```sh
|
||
|
|
argocd app sync demo
|
||
|
|
```
|
||
|
|
|
||
|
|
4. Watch it happen:
|
||
|
|
```sh
|
||
|
|
argocd app get demo
|
||
|
|
```
|
||
|
|
You'll see Argo CD detect that the live ConfigMap no longer matches
|
||
|
|
Git, and correct it.
|
||
|
|
|
||
|
|
5. Refresh `http://<your-demo-app-IP>` (the MetalLB address you gave it in
|
||
|
|
[`docs/05-metallb.md`](05-metallb.md)). Your new text should be there. Note
|
||
|
|
that nginx itself never restarted — Kubernetes noticed the mounted
|
||
|
|
ConfigMap changed and updated the file inside the running Pod's
|
||
|
|
filesystem automatically. (This is specific to volume-mounted
|
||
|
|
ConfigMaps; not every kind of change is this seamless — a change to the
|
||
|
|
Deployment's image, for instance, does trigger a Pod restart, by
|
||
|
|
design.)
|
||
|
|
|
||
|
|
Give it up to a minute if the page doesn't look different yet.
|
||
|
|
`argocd app get demo` shows the *ConfigMap object* updating right away,
|
||
|
|
but kubelet — the agent on the node that actually keeps a Pod's mounted
|
||
|
|
files in sync — only re-checks mounted ConfigMaps on its own periodic
|
||
|
|
cycle, not instantly. A blank refresh isn't a sign anything's wrong;
|
||
|
|
give it a moment and refresh again.
|
||
|
|
|
||
|
|
## What just proved itself
|
||
|
|
|
||
|
|
You changed a file, pushed it, and never touched the cluster directly. That
|
||
|
|
gap between "commit" and "running" being closed automatically, without you
|
||
|
|
doing the applying, *is* GitOps. Everything from here on — every future app
|
||
|
|
you add — works exactly this way: edit, commit, push, done.
|
||
|
|
|
||
|
|
## Try triggering self-healing
|
||
|
|
|
||
|
|
Optional, but worth seeing once. Reintroduce drift by hand:
|
||
|
|
|
||
|
|
```sh
|
||
|
|
kubectl -n demo patch configmap demo-page --type merge \
|
||
|
|
-p '{"data":{"index.html":"<h1>hand-edited, not from Git</h1>"}}'
|
||
|
|
```
|
||
|
|
|
||
|
|
Watch the ConfigMap *object* itself, not the browser, for this one — it's
|
||
|
|
the more reliable way to see the timing: Argo CD's self-heal typically
|
||
|
|
reverts a hand-edit within a second or two, which is faster than kubelet's
|
||
|
|
own mount-sync cycle usually gets around to reflecting a change in the
|
||
|
|
served page at all (see the note above). Check the object directly:
|
||
|
|
|
||
|
|
```sh
|
||
|
|
kubectl -n demo get configmap demo-page -o jsonpath='{.data.index\.html}'
|
||
|
|
```
|
||
|
|
|
||
|
|
Run that once right after the `patch` above and you may catch your
|
||
|
|
hand-edited text; run it again a couple of seconds later and it'll already
|
||
|
|
be back to what's in Git — with no action from you. That's `selfHeal:
|
||
|
|
true` from `apps/demo.yaml` in action. See
|
||
|
|
[`docs/00-what-is-all-this.md`](00-what-is-all-this.md#the-reconciliation-loop)
|
||
|
|
for the loop that just ran.
|
||
|
|
|
||
|
|
> **Ask Claude:** "if selfHeal is on, how would I ever safely debug
|
||
|
|
> something by changing it live in the cluster first?" — a real question
|
||
|
|
> people run into once this clicks, and worth understanding before you hit
|
||
|
|
> it for real.
|
||
|
|
|
||
|
|
## Checklist
|
||
|
|
|
||
|
|
- [ ] Edited `apps/demo/configmap.yaml`, committed, pushed
|
||
|
|
- [ ] Saw the change reflected in `argocd app get demo`
|
||
|
|
- [ ] Saw the new text in the browser
|
||
|
|
- [ ] (Optional) Watched self-healing revert a hand-made change
|
||
|
|
|
||
|
|
Continue to [`docs/07-adding-new-apps.md`](07-adding-new-apps.md) to add
|
||
|
|
something of your own.
|