**When:** During pre-defined window in Thursday 21st 2022
**Checklist:**
NEW primary: db1104
OLD primary: db1109
[x] Check configuration differences between new and old primary:
```
sudo pt-config-diff --defaults-file /root/.my.cnf h=db1109.eqiad.wmnet h=db1104.eqiad.wmnet
```
**Failover prep:**
[x] Silence alerts on all hosts:
```
sudo cookbook sre.hosts.downtime --hours 1 -r "Primary switchover s8 T303927" 'A:db-section-s8'
```
[x] Set NEW primary with weight 0
```
sudo dbctl instance db1104 set-weight 0
sudo dbctl config commit -m "Set db1104 with weight 0 T303927"
```
[x] Topology changes, move all replicas under NEW primary
```
sudo db-switchover --timeout=25 --only-slave-move db1109 db1104
```
[x] Disable puppet on both nodes
```
sudo cumin 'db1109* or db1104*' 'disable-puppet "primary switchover T303927"'
```
[x] Merge gerrit puppet change to promote NEW primary: https://gerrit.wikimedia.org/r/c/operations/puppet/+/784681
**Failover:**
[] Log the failover:
```
!log Starting s8 eqiad failover from db1109 to db1104 - T303927
```
[] Set section read-only:
```
sudo dbctl --scope eqiad section s8 ro "Maintenance until 06:15 UTC - T303927"
sudo dbctl config commit -m "Set s8 eqiad as read-only for maintenance - T303927"
```
[] Check s8 is indeed read-only
[] Switch primaries:
```
sudo db-switchover --skip-slave-move db1109 db1104
echo "===== db1109 (OLD)"; sudo db-mysql db1109 -e 'show slave status\G'
echo "===== db1104 (NEW)"; sudo db-mysql db1104 -e 'show slave status\G'
```
[] Promote NEW primary in dbctl, and remove read-only
```
sudo dbctl --scope eqiad section s8 set-master db1104
sudo dbctl --scope eqiad section s8 rw
sudo dbctl config commit -m "Promote db1104 to s8 primary and set section read-write T303927"
```
[] Restart puppet on both hosts:
```
sudo cumin 'db1109* or db1104*' 'run-puppet-agent -e "primary switchover T303927"'
```
**Clean up tasks:**
[] Clean up heartbeat table(s): `delete from heartbeat.heartbeat where server_id=171978924`
[] change events for query killer:
```
events_coredb_master.sql on the new primary db1104
events_coredb_slave.sql on the new slave db1109
```
[] Update DNS: https://gerrit.wikimedia.org/r/c/operations/dns/+/784678
[] Update candidate primary dbctl and orchestrator notes
```
sudo dbctl instance db1109 set-candidate-master --section s8 true
sudo dbctl instance db1104 set-candidate-master --section s8 false
(dborch1001): sudo orchestrator-client -c untag -i db1104 --tag name=candidate
(dborch1001): sudo orchestrator-client -c tag -i db1109 --tag name=candidate
```
[] Check zarcillo was updated
** db-switchover should do this. If it fails, do it manually: https://phabricator.wikimedia.org/P13956
[] (If needed): Depool db1109 for maintenance.
```
sudo dbctl instance db1109 depool
sudo dbctl config commit -m "Depool db1109 T303927"
```
[] Apply outstanding schema changes to db1109 (if any)
[] Update/resolve this ticket.