**When:** During a pre-defined DBA maintenance windows
**Prerequisites:** https://wikitech.wikimedia.org/wiki/MariaDB/Primary_switchover
[] Team calendar invite
**Affected wikis:**: https://noc.wikimedia.org/conf/highlight.php?file=dblists/s1.dblist
**Checklist:**
NEW primary: db2112
OLD primary: db2103
[x] Check configuration differences between new and old primary:
```
sudo pt-config-diff --defaults-file /root/.my.cnf h=db2103.codfw.wmnet h=db2112.codfw.wmnet
```
**Failover prep:**
[x] Silence alerts on all hosts:
```
sudo cookbook sre.hosts.downtime --hours 1 -r "Primary switchover s1 T356059" 'A:db-section-s1'
```
[x] Set NEW primary with weight 0 (and depool it from API or vslow/dump groups if it is present).
```
sudo dbctl instance db2112 set-weight 0
sudo dbctl config commit -m "Set db2112 with weight 0 T356059"
```
[x] Topology changes, move all replicas under NEW primary
```
sudo db-switchover --timeout=25 --only-slave-move db2103 db2112
```
[x] Disable puppet on both nodes
```
sudo cumin 'db2103* or db2112*' 'disable-puppet "primary switchover T356059"'
```
[x] Merge gerrit puppet change to promote NEW primary: https://gerrit.wikimedia.org/r/c/operations/puppet/+/993469
**Failover:**
[] Log the failover:
```
!log Starting s1 codfw failover from db2103 to db2112 - T356059
```
[] Set section read-only:
```
sudo dbctl --scope eqiad section s1 ro "Maintenance until 06:15 UTC - T356059"
sudo dbctl --scope codfw section s1 ro "Maintenance until 06:15 UTC - T356059"
sudo dbctl config commit -m "Set s1 codfw as read-only for maintenance - T356059"
```
[] Check s1 is indeed read-only
[] Switch primaries:
```
sudo db-switchover --skip-slave-move db2103 db2112
echo "===== db2103 (OLD)"; sudo db-mysql db2103 -e 'show slave status\G'
echo "===== db2112 (NEW)"; sudo db-mysql db2112 -e 'show slave status\G'
```
[] Promote NEW primary in dbctl, and remove read-only
```
sudo dbctl --scope codfw section s1 set-master db2112
sudo dbctl --scope eqiad section s1 rw
sudo dbctl --scope codfw section s1 rw
sudo dbctl config commit -m "Promote db2112 to s1 primary and set section read-write T356059"
```
[] Restart puppet on both hosts:
```
sudo cumin 'db2103* or db2112*' 'run-puppet-agent -e "primary switchover T356059"'
```
**Clean up tasks:**
[] Clean up heartbeat table(s).
```
sudo db-mysql db2112 heartbeat -e "delete from heartbeat where file like 'db2103%';"
```
[] change events for query killer:
```
events_coredb_master.sql on the new primary db2112
events_coredb_slave.sql on the new slave db2103
```
[] Update DNS: https://gerrit.wikimedia.org/r/c/operations/dns/+/993470
[] Update candidate primary dbctl and orchestrator notes
```
sudo dbctl instance db2103 set-candidate-master --section s1 true
sudo dbctl instance db2112 set-candidate-master --section s1 false
(dborch1001): sudo orchestrator-client -c untag -i db2112 --tag name=candidate
(dborch1001): sudo orchestrator-client -c tag -i db2103 --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 db1215 zarcillo -e "select * from masters where section = 's1';"
```
[] (If needed): Depool db2103 for maintenance.
```
sudo dbctl instance db2103 depool
sudo dbctl config commit -m "Depool db2103 T356059"
```
[] Change db2103 weight to mimic the previous weight db2112:
```
sudo dbctl instance db2103 edit
```
[] Apply outstanding schema changes to db2103 (if any)
[] Update/resolve this ticket.