jakman85andClaude Opus 5
5642881c4d
MEASURED on prod 2026-10-18: kube-system/coredns had replicas: 1. In-cluster DNS was a single pod on a single node, so draining or rebooting that node was a CLUSTER-WIDE in-cluster DNS outage until the pod rescheduled -- every Service lookup, every CNPG replica finding its primary, every operator addressing the API by name. It was invisible because 1/1 Ready looks healthy. It is urgent rather than latent now: the scheduled reboot automation on feat/automated-upgrades drains and reboots one node at a time, unattended, overnight -- turning a single point of failure into a recurring one. WHY AN HPA AND NOT replicas: 2 -- the whole decision. k3s OWNS the coredns Deployment: AddOn/coredns, source /data/k3s/server/manifests/coredns.yaml, managedFields managers deploy@k3s-prod-1 + k3s, objectset.rio.cattle.io/hash label. k3s re-stages its bundled manifests on startup, so replicas: 2 written there -- or a kubectl scale -- is reverted on the next restart or upgrade. Rejected alternatives: * coredns.yaml.skip + our own templated copy (the roles/kube_vip pattern). Deterministic, but takes ownership of coredns from k3s permanently so k3s upgrades stop updating it. Too high a price for a replica count. * A Flux patch of the Deployment. Rejected outright: Flux and k3s's deploy controller would both own one object and fight -- the default-deny NetworkPolicy drift-loop shape (~2500 events/10min) this cluster already hit. An HPA is a separate object k3s does not own, driving /scale rather than the Deployment spec, so there is no shared-ownership fight; if k3s re-stages replicas: 1 it is re-asserted within a reconcile. Disclosed cost: a brief window at 1 replica after a k3s restart. It is a FLOOR-HOLDER, not an autoscaler -- the CPU metric exists only so the autoscaling/v2 object is valid. Measured: 5m/4m against a 100m request (~5%), so the 80% target is never approached. scaleDown stabilization 600s because DNS is the worst thing to flap; scaleUp immediate, since that restores redundancy. The kustomization edit is ADDITIVE: platform/coredns/ already existed and holds the coredns-custom split-horizon ConfigMap (R-DNS-01/03), which is untouched. UNAPPLIED. The HPA has never run, and the claim that k3s reverts replicas on restart is reasoned, not observed. After merge check `describe hpa coredns` for ScalingActive=True -- an inert HPA looks identical to a working one because the hand scale already left 2 replicas. See the handoff entry. Co-Authored-By: Claude Opus 5 (1M context) <[email protected]>
decisions/ — the handoff log, one file per entry
This directory is the decision log. ../DECISIONS-LOG.md is the frozen archive of
everything written before 2026-09-29 and is never edited again (see "The archive is
frozen" below).
Why this exists
DECISIONS-LOG.md was append-only in a single file, and every agent appended to its
tail. Two branches that both append hit the same last hunk, so git cannot
auto-merge them: the second one to be reviewed conflicts, and so does the third, and
the fourth. Measured on 2026-09-29: four of the five open PRs were unmergeable, and
DECISIONS-LOG.md was the only conflicting file in all four:
#22 fix/crafty-oauth2-proxy-signin CONFLICT (content): DECISIONS-LOG.md
#20 feat/conformance-job-template CONFLICT (content): DECISIONS-LOG.md
#19 feat/conformance-trigger-kubeconfig CONFLICT (content): DECISIONS-LOG.md
#18 feat/conformance-runner-image CONFLICT (content): DECISIONS-LOG.md
#17 feat/ci-is-the-approver clean (it touched no log entry)
Nothing was wrong with any of those changes. The log's storage format serialised work that was otherwise parallel, and it got worse with every concurrent branch: N branches produce N-1 rebases, each of which invalidates any gate run that preceded it.
The fix is the obvious one for concurrent appenders: stop sharing a file. Each
handoff is its own file. Two agents writing handoffs touch disjoint paths, so there is
nothing for git to merge and nothing to conflict. This scales to any number of parallel
branches with zero coordination — which is the point, since the agents are deliberately
isolated from each other in separate worktrees (required by CLAUDE.md §0) and cannot
coordinate.
There is deliberately no index file and no counter. An index would be a shared
mutable file — exactly the thing that just failed — and a sequence number would have
two agents racing for 0043. The directory listing is the index.
Writing an entry
One file per handoff, named:
decisions/YYYY-MM-DD-<slug>.md
<slug> is lowercase [a-z0-9-]. Use your branch name's last segment — it is
already unique per unit of work, which is precisely the property the filename needs.
A branch fix/crafty-oauth2-proxy-signin handed off on 2026-09-29 writes:
decisions/2026-09-29-crafty-oauth2-proxy-signin.md
The file is YAML frontmatter followed by three required sections:
---
date: 2026-09-29
branch: fix/crafty-oauth2-proxy-signin
title: The Keycloak gate works — Crafty's own login was the wall
---
## What changed
Prose. What you actually did, and why.
## What I verified
The measurements, with their numbers. Quote the field you read, not the prose you
believed. Name the gate result and its exit code.
## What I did NOT verify
Everything else. An honest "UNVERIFIED" is worth more than an optimistic "green" —
this repo has been burned by the difference more than once.
All three headings are required and enforced (ci/decisions-log.sh). They are
CLAUDE.md §7's contract; making them a checked structure is what stops an entry
degrading into "done ✅".
Reading the log
The whole log, oldest first:
ls decisions/[0-9]*.md | sort
The current PM handoff — the newest entry. Ties within a day are broken by what landed
on main last, which is the honest answer, so ask git rather than the filename:
git log --diff-filter=A --format='%H' --name-only -- 'decisions/[0-9]*.md' \
| grep '^decisions/' | head -1
For a quick skim of who said what:
grep -H '^title:' decisions/[0-9]*.md | sort
The archive is frozen
DECISIONS-LOG.md is read-only history. Its SHA-256 is pinned in
decisions/ARCHIVE.sha256 and ci/decisions-log.sh fails the merge gate if the file
changes. That is not ceremony: without it, the next agent to read runbooks/ or an old
CLAUDE.md habit appends to the tail again and re-creates the conflict for everybody
else, silently, one PR at a time.
If the archive genuinely must change (a leaked credential to redact, say), that is a
deliberate, reviewed act: change it, run sha256sum DECISIONS-LOG.md > decisions/ARCHIVE.sha256,
and say in your handoff entry why. Re-pinning is visible in the diff. Appending is not.