**When:** FIXME
**Checklist:**
[] Create a task to communicate the chosen date and send an announcement to the community: FIXME
[] Create a calendar entry for the maintenance, invite sre-data-persistence@
[] Add to deployments calendar. E.g.:
```
{{Deployment calendar event card
|when=2021-08-24 23:00 SF
|length=0.5
|window=Database primary switchover for s7
|who={{ircnick|kormat|Stevie Beth Mhaol}}, {{ircnick|marostegui|Manuel 'Early Bird' Arostegui}}
|what=https://phabricator.wikimedia.org/T289650
}}
```
NEW primary: db2110
OLD primary: db2090
[] Check configuration differences between new and old primary:
```
sudo pt-config-diff --defaults-file /root/.my.cnf h=db2090.codfw.wmnet h=db2110.codfw.wmnet
```
**Failover prep:**
[] Silence alerts on all hosts:
```
sudo cookbook sre.hosts.downtime --hours 1 -r "Primary switchover s4 T289650" 'A:db-section-s4'
```
[] Set NEW primary with weight 0
```
sudo dbctl instance db2110 set-weight 0
sudo dbctl config commit -m "Set db2110 with weight 0 T289650"
```
[] Topology changes, move all replicas under NEW primary
```
sudo db-switchover --timeout=15 --only-slave-move db2090 db2110
```
[] Disable puppet on both nodes
```
sudo cumin 'db2090* or db2110*' 'disable-puppet "primary switchover T289650"'
```
[] Merge gerrit puppet change to promote NEW primary: FIXME
**Failover:**
[] Log the failover:
```
!log Starting s4 codfw failover from db2090 to db2110 - T289650
```
[] Set section read-only:
```
sudo dbctl --scope codfw section s4 ro "Maintenance until 05:15 UTC - T289650"
sudo dbctl config commit -m "Set s4 codfw as read-only for maintenance - T289650"
```
[] Check s4 is indeed read-only
[] Switch primaries:
```
sudo db-switchover --skip-slave-move db2090 db2110
echo "===== db2090 (OLD)"; sudo mysql.py -h db2090 -e 'show slave status\G'
echo "===== db2110 (NEW)"; sudo mysql.py -h db2110 -e 'show slave status\G'
```
[] Promote NEW primary in dbctl, and remove read-only
```
sudo dbctl --scope codfw section s4 set-master db2110
sudo dbctl --scope codfw section s4 rw
sudo dbctl config commit -m "Promote db2110 to s4 primary and set section read-write T289650"
```
[] Restart puppet on both hosts:
```
sudo cumin 'db2090* or db2110*' 'run-puppet-agent -e "primary switchover T289650"'
```
**Clean up tasks:**
[] Clean up heartbeat table(s).
[] change events for query killer:
```
events_coredb_master.sql on the new primary db2110
events_coredb_slave.sql on the new slave db2090
```
[] Update DNS: FIXME
[] Update candidate primary dbctl notes
```
sudo dbctl instance db2090 set-candidate-master --section s4 true
sudo dbctl instance db2110 set-candidate-master --section s4 false
```
[] Check tendril was updated
[] Check zarcillo was updated
** db-switchover should do this. If it fails, do it manually: https://phabricator.wikimedia.org/P13956
[] Depool OLD primary, as it's running 10.1, replicating from a 10.4 primary
```
sudo dbctl instance db2090 depool
sudo dbctl config commit -m "Depool db2090 until it's reimaged to buster T289650"
```
[] Apply outstanding schema changes to db2090 (if any)
[] Update/resolve this ticket.