**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/s3.dblist
**Checklist:**
NEW primary: db1123
OLD primary: db1157
[] Check configuration differences between new and old primary:
```
sudo pt-config-diff --defaults-file /root/.my.cnf h=db1157.eqiad.wmnet h=db1123.eqiad.wmnet
```
**Failover prep:**
[] Silence alerts on all hosts:
```
sudo cookbook sre.hosts.downtime --hours 1 -r "Primary switchover s3 T316622" 'A:db-section-s3'
```
[] Set NEW primary with weight 0 (and depool it from API or vslow/dump groups if it is present).
```
sudo dbctl instance db1123 set-weight 0
sudo dbctl config commit -m "Set db1123 with weight 0 T316622"
```
[] Topology changes, move all replicas under NEW primary
```
sudo db-switchover --timeout=25 --only-slave-move db1157 db1123
```
[] Disable puppet on both nodes
```
sudo cumin 'db1157* or db1123*' 'disable-puppet "primary switchover T316622"'
```
[] Merge gerrit puppet change to promote NEW primary: FIXME
**Failover:**
[] Log the failover:
```
!log Starting s3 eqiad failover from db1157 to db1123 - T316622
```
[] Set section read-only:
```
sudo dbctl --scope eqiad section s3 ro "Maintenance until 06:15 UTC - T316622"
sudo dbctl config commit -m "Set s3 eqiad as read-only for maintenance - T316622"
```
[] Check s3 is indeed read-only
[] Switch primaries:
```
sudo db-switchover --skip-slave-move db1157 db1123
echo "===== db1157 (OLD)"; sudo db-mysql db1157 -e 'show slave status\\G'
echo "===== db1123 (NEW)"; sudo db-mysql db1123 -e 'show slave status\\G'
```
[] Promote NEW primary in dbctl, and remove read-only
```
sudo dbctl --scope eqiad section s3 set-master db1123
sudo dbctl --scope eqiad section s3 rw
sudo dbctl config commit -m "Promote db1123 to s3 primary and set section read-write T316622"
```
[] Restart puppet on both hosts:
```
sudo cumin 'db1157* or db1123*' 'run-puppet-agent -e "primary switchover T316622"'
```
**Clean up tasks:**
[] Clean up heartbeat table(s).
```
sudo db-mysql db1123 heartbeat -e "delete from heartbeat where file like 'db1157%';"
```
[] change events for query killer:
```
events_coredb_master.sql on the new primary db1123
events_coredb_slave.sql on the new slave db1157
```
[] Update DNS: FIXME
[] Update candidate primary dbctl and orchestrator notes
```
sudo dbctl instance db1157 set-candidate-master --section s3 true
sudo dbctl instance db1123 set-candidate-master --section s3 false
(dborch1001): sudo orchestrator-client -c untag -i db1123 --tag name=candidate
(dborch1001): sudo orchestrator-client -c tag -i db1157 --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 = 's3';"
```
[] (If needed): Depool db1157 for maintenance.
```
sudo dbctl instance db1157 depool
sudo dbctl config commit -m "Depool db1157 T316622"
```
[] Change db1157 weight to mimic the previous weight db1123:
```
sudo dbctl instance db1157 edit
```
[] Apply outstanding schema changes to db1157 (if any)
[] Update/resolve this ticket.