---
# Give the k3s server process — and therefore the EMBEDDED ETCD inside it — a larger share of
# the block device it shares with Longhorn. Mitigates the 2026-09-07 k3s-prod-1 outage, where
# etcd's WAL fdatasync took 3.4-6.7 s (expects 1 s) and the node went NotReady while the host
# stayed up. See roles/etcd_io_priority/README.md for the mechanism, the measurements, and the
# list of things in this space that do NOT work on these nodes.
#
# NO-OP BY DEFAULT. The role's master switch (etcd_io_priority_enabled) is false in
# defaults/main.yml and true only in inventory/group_vars/k3s_prod/vars.yml, so running this
# with no extra vars against dev changes nothing on any node — dev already has a dedicated
# etcd device and has nothing to arbitrate.
#
# TARGET (R-ENV-02): same `k3s_hosts` seam every other whole-cluster play uses.
#   ansible-playbook playbooks/etcd-io-priority.yml                       # dev, a no-op
#   ansible-playbook playbooks/etcd-io-priority.yml -e k3s_hosts=k3s_prod # prod
#
# RUN IT ON ONE NODE FIRST, AND CONFIRM THE TARGET BEFORE YOU RUN IT AT ALL. A prior mistake in
# this repo silently targeted dev's three nodes; --list-hosts is how that is caught:
#   ansible-playbook playbooks/etcd-io-priority.yml -e k3s_hosts=k3s_prod \
#     --limit k3s-prod-3 --list-hosts
# k3s-prod-3 first, deliberately: it is the WD Blue SATA node (IO PSI 1.29 during the incident),
# so it exercises the identical code path as the failing node 1 (11.36) at a fraction of the
# stakes. Watch NodeIOPressureHigh / the "Nodes — CPU / Memory / I-O Pressure" dashboard for a
# day before touching node 1.
#
# ROLLBACK is immediate and needs no playbook — see the header of
# /usr/local/sbin/k3s-etcd-io-priority on the node.

- name: I/O priority for the shared etcd + Longhorn device
  hosts: "{{ k3s_hosts | default('k3s_servers') }}"
  become: true
  # serial: 1 — one node at a time. Nothing here restarts k3s, but changing a live node's I/O
  # scheduler is a real change to a cluster member, and the whole point is that a bad outcome
  # on one node must never be simultaneous across all three.
  serial: 1
  gather_facts: true
  roles:
    - role: etcd_io_priority