**When:** During a pre-defined DBA maintenance windows
**Prerequisites:** https://wikitech.wikimedia.org/wiki/MariaDB/Primary_switchover
**Affected wikis:**: https://noc.wikimedia.org/conf/highlight.php?file=dblists/s1.dblist
**Checklist:**
NEW primary: db2212
OLD primary: db2203
[] Check configuration differences between new and old primary:
```
sudo pt-config-diff --defaults-file /root/.my.cnf h=db2203.codfw.wmnet h=db2212.codfw.wmnet
```
**Failover prep:**
[] Silence alerts on all hosts:
```
sudo cookbook sre.hosts.downtime --hours 1 -r "Primary switchover s1 T416554" 'A:db-section-s1'
```
[] Set NEW primary with weight 0
```
sudo dbctl instance db2212 set-weight 0
sudo dbctl config commit -m "Set db2212 with weight 0 T416554"
```
[] Topology changes, move all replicas under NEW primary, open orchestartor to monitor the process and check it at the end.
```
sudo db-switchover --timeout=25 --only-slave-move db2203 db2212
```
[] Disable puppet on both nodes
```
sudo cumin 'db2203* or db2212*' 'disable-puppet "primary switchover T416554"'
```
[] Merge gerrit puppet change to promote NEW primary: https://gerrit.wikimedia.org/r/1237136
**Failover:**
[] Log the failover:
```
!log Starting s1 codfw failover from db2203 to db2212 - T416554
```
[] Set section read-only:
```
sudo dbctl --scope eqiad section s1 ro "Maintenance until 06:15 UTC - T416554"
sudo dbctl --scope codfw section s1 ro "Maintenance until 06:15 UTC - T416554"
sudo dbctl config commit -m "Set s1 codfw as read-only for maintenance - T416554"
```
[] Check s1 is indeed read-only
[] Switch primaries:
```
sudo db-switchover --skip-slave-move db2203 db2212
echo "===== db2203 (OLD)"; sudo db-mysql db2203 -e 'show slave status\G'
echo "===== db2212 (NEW)"; sudo db-mysql db2212 -e 'show slave status\G'
```
[] Promote NEW primary in dbctl, and remove read-only
```
sudo dbctl --scope codfw section s1 set-master db2212
sudo dbctl --scope eqiad section s1 rw
sudo dbctl --scope codfw section s1 rw
sudo dbctl config commit -m "Promote db2212 to s1 primary and set section read-write T416554"
```
[] Clean up heartbeat table(s).
```
sudo db-mysql db2212 heartbeat -e "delete from heartbeat where file like 'db2203%';"
```
[] Restart puppet on both hosts:
```
sudo cumin 'db2203* or db2212*' 'run-puppet-agent -e "primary switchover T416554"'
```
**Clean up tasks:**
[] change events for query killer:
```
curl -sS 'https://gerrit.wikimedia.org/r/plugins/gitiles/operations/software/+/refs/heads/master/dbtools/events_coredb_master.sql?format=TEXT' | base64 -d | sudo db-mysql db2212
curl -sS 'https://gerrit.wikimedia.org/r/plugins/gitiles/operations/software/+/refs/heads/master/dbtools/events_coredb_slave.sql?format=TEXT' | base64 -d | sudo db-mysql db2203
```
[] Merge DNS change (ssh ns0.wikimedia.org): https://gerrit.wikimedia.org/r/1237137
```
sudo authdns-update
```
[] Update candidate primary dbctl and orchestrator notes
```
sudo dbctl instance db2203 set-candidate-master --section s1 true
sudo dbctl instance db2212 set-candidate-master --section s1 false
sudo cumin 'dborch*' 'orchestrator-client -c untag -i db2212 --tag name=candidate'
sudo cumin 'dborch*' 'orchestrator-client -c tag -i db2203 --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';"
```
[] Depool db2203 for maintenance.
```
sudo dbctl instance db2203 depool
sudo dbctl config commit -m "Depool db2203 T416554"
```
[] Change db2203 weight to mimic the previous weight db2212:
```
sudo dbctl instance db2203 edit
```
[] Apply outstanding schema changes to db2203 (if any)
[] Slowly repool the db2203 if ready
```
sudo cookbook sre.mysql.pool -t T416554 -r "Repooling after switchover" db2203
```
[] Update/resolve this ticket.