**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/s2.dblist
**Checklist:**
NEW primary: db1162
OLD primary: db1222
[] Check configuration differences between new and old primary:
```
sudo pt-config-diff --defaults-file /root/.my.cnf h=db1222.eqiad.wmnet h=db1162.eqiad.wmnet
```
**Failover prep:**
[] Silence alerts on all hosts:
```
sudo cookbook sre.hosts.downtime --hours 1 -r "Primary switchover s2 T367020" 'A:db-section-s2'
```
[] Set NEW primary with weight 0
```
sudo dbctl instance db1162 set-weight 0
sudo dbctl config commit -m "Set db1162 with weight 0 T367020"
```
[] Depool NEW from any specific group (API, vslow, dump) if present.
```
sudo dbctl instance db1162 edit
# If some changes were made:
sudo dbctl config commit -m "Remove db1162 from API/vslow/dump T367020"
```
[] Topology changes, move all replicas under NEW primary
```
sudo db-switchover --timeout=25 --only-slave-move db1222 db1162
```
[] Disable puppet on both nodes
```
sudo cumin 'db1222* or db1162*' 'disable-puppet "primary switchover T367020"'
```
[] Merge gerrit puppet change to promote NEW primary: https://gerrit.wikimedia.org/r/c/operations/puppet/+/1040886
**Failover:**
[] Log the failover:
```
!log Starting s2 eqiad failover from db1222 to db1162 - T367020
```
[] Set section read-only:
```
sudo dbctl --scope eqiad section s2 ro "Maintenance until 06:15 UTC - T367020"
sudo dbctl --scope codfw section s2 ro "Maintenance until 06:15 UTC - T367020"
sudo dbctl config commit -m "Set s2 eqiad as read-only for maintenance - T367020"
```
[] Check s2 is indeed read-only
[] Switch primaries:
```
sudo db-switchover --skip-slave-move db1222 db1162
echo "===== db1222 (OLD)"; sudo db-mysql db1222 -e 'show slave status\G'
echo "===== db1162 (NEW)"; sudo db-mysql db1162 -e 'show slave status\G'
```
[] Promote NEW primary in dbctl, and remove read-only
```
sudo dbctl --scope eqiad section s2 set-master db1162
sudo dbctl --scope eqiad section s2 rw
sudo dbctl --scope codfw section s2 rw
sudo dbctl config commit -m "Promote db1162 to s2 primary and set section read-write T367020"
```
[] Restart puppet on both hosts:
```
sudo cumin 'db1222* or db1162*' 'run-puppet-agent -e "primary switchover T367020"'
```
**Clean up tasks:**
[] Clean up heartbeat table(s).
```
sudo db-mysql db1162 heartbeat -e "delete from heartbeat where file like 'db1222%';"
```
[] change events for query killer:
```
events_coredb_master.sql on the new primary db1162
events_coredb_slave.sql on the new slave db1222
```
[] Update DNS: https://gerrit.wikimedia.org/r/c/operations/dns/+/1040887
[] Update candidate primary dbctl and orchestrator notes
```
sudo dbctl instance db1222 set-candidate-master --section s2 true
sudo dbctl instance db1162 set-candidate-master --section s2 false
(dborch1001): sudo orchestrator-client -c untag -i db1162 --tag name=candidate
(dborch1001): sudo orchestrator-client -c tag -i db1222 --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 = 's2';"
```
[] (If needed): Depool db1222 for maintenance.
```
sudo dbctl instance db1222 depool
sudo dbctl config commit -m "Depool db1222 T367020"
```
[] Change db1222 weight to mimic the previous weight db1162:
```
sudo dbctl instance db1222 edit
```
[] Apply outstanding schema changes to db1222 (if any)
[] Update/resolve this ticket.