**When:** During a pre-defined DBA maintenance windows
**Prerequisites:** https://wikitech.wikimedia.org/wiki/MariaDB/Primary_switchover
[] Team calendar invite
**Affected wikis:**: TO-DO
**Checklist:**
NEW primary: db1120
OLD primary: db1103
[] Check configuration differences between new and old primary:
```
sudo pt-config-diff --defaults-file /root/.my.cnf h=db1103.eqiad.wmnet h=db1120.eqiad.wmnet
```
**Failover prep:**
[] Silence alerts on all hosts:
```
sudo cookbook sre.hosts.downtime --hours 1 -r "Primary switchover x1 T316745" 'A:db-section-x1'
```
[] Set NEW primary with weight 0 (and depool it from API or vslow/dump groups if it is present).
```
sudo dbctl instance db1120 set-weight 0
sudo dbctl config commit -m "Set db1120 with weight 0 T316745"
```
[] Topology changes, move all replicas under NEW primary
```
sudo db-switchover --timeout=25 --only-slave-move db1103 db1120
```
[] Disable puppet on both nodes
```
sudo cumin 'db1103* or db1120*' 'disable-puppet "primary switchover T316745"'
```
[] Merge gerrit puppet change to promote NEW primary: https://gerrit.wikimedia.org/r/c/operations/puppet/+/828468
**Failover:**
[] Log the failover:
```
!log Starting x1 eqiad failover from db1103 to db1120 - T316745
```
[] Set section read-only:
```
sudo dbctl --scope eqiad section x1 ro "Maintenance until 06:15 UTC - T316745"
sudo dbctl config commit -m "Set x1 eqiad as read-only for maintenance - T316745"
```
[] Check x1 is indeed read-only
[] Switch primaries:
```
sudo db-switchover --skip-slave-move db1103 db1120
echo "===== db1103 (OLD)"; sudo db-mysql db1103 -e 'show slave status\\G'
echo "===== db1120 (NEW)"; sudo db-mysql db1120 -e 'show slave status\\G'
```
[] Promote NEW primary in dbctl, and remove read-only
```
sudo dbctl --scope eqiad section x1 set-master db1120
sudo dbctl --scope eqiad section x1 rw
sudo dbctl config commit -m "Promote db1120 to x1 primary and set section read-write T316745"
```
[] Restart puppet on both hosts:
```
sudo cumin 'db1103* or db1120*' 'run-puppet-agent -e "primary switchover T316745"'
```
**Clean up tasks:**
[] Clean up heartbeat table(s).
```
sudo db-mysql db1120 heartbeat -e "delete from heartbeat where file like 'db1103%';"
```
[] change events for query killer:
```
events_coredb_master.sql on the new primary db1120
events_coredb_slave.sql on the new slave db1103
```
[] Update DNS: https://gerrit.wikimedia.org/r/828469
[] Update candidate primary dbctl and orchestrator notes
```
sudo dbctl instance db1103 set-candidate-master --section x1 true
sudo dbctl instance db1120 set-candidate-master --section x1 false
(dborch1001): sudo orchestrator-client -c untag -i db1120 --tag name=candidate
(dborch1001): sudo orchestrator-client -c tag -i db1103 --tag name=candidate
```
[] Check zarcillo was updated
** db-switchover should do this. If it fails, do it manually: https://phabricator.wikimedia.org/P13956
```
sudo db-mysql db1115 zarcillo -e "select * from masters where section = 'x1';"
```
[] (If needed): Depool db1103 for maintenance.
```
sudo dbctl instance db1103 depool
sudo dbctl config commit -m "Depool db1103 T316745"
```
[] Change db1103 weight to mimic the previous weight db1120:
```
sudo dbctl instance db1103 edit
```
[] Apply outstanding schema changes to db1103 (if any)
[] Update/resolve this ticket.