**When:** During a pre-defined DBA maintenance windows
**Affected wikis:**: https://noc.wikimedia.org/conf/highlight.php?file=dblists/s4.dblist
**Checklist:**
NEW primary: db2140
OLD primary: db2110
[] Check configuration differences between new and old primary:
```
sudo pt-config-diff --defaults-file /root/.my.cnf h=db2110.codfw.wmnet h=db2140.codfw.wmnet
```
**Failover prep:**
[] Silence alerts on all hosts:
```
sudo cookbook sre.hosts.downtime --hours 1 -r "Primary switchover s4 T328022" 'A:db-section-s4'
```
[] Set NEW primary with weight 0 (and depool it from API or vslow/dump groups if it is present).
```
sudo dbctl instance db2140 set-weight 0
sudo dbctl config commit -m "Set db2140 with weight 0 T328022"
```
[] Topology changes, move all replicas under NEW primary
```
sudo db-switchover --timeout=25 --replicating-master --read-only-master --only-slave-move db2110 db2140
```
[] Disable puppet on both nodes
```
sudo cumin 'db2110* or db2140*' 'disable-puppet "primary switchover T328022"'
```
[] Merge gerrit puppet change to promote NEW primary: FIXME
**Failover:**
[] Log the failover:
```
!log Starting s4 codfw failover from db2110 to db2140 - T328022
```
[] Switch primaries:
```
sudo db-switchover --replicating-master --read-only-master --skip-slave-move db2110 db2140
echo "===== db2110 (OLD)"; sudo db-mysql db2110 -e 'show slave status\\G'
echo "===== db2140 (NEW)"; sudo db-mysql db2140 -e 'show slave status\\G'
```
[] Promote NEW primary in dbctl
```
sudo dbctl --scope codfw section s4 set-master db2140
sudo dbctl config commit -m "Promote db2140 to s4 primary T328022"
```
[] Restart puppet on both hosts:
```
sudo cumin 'db2110* or db2140*' 'run-puppet-agent -e "primary switchover T328022"'
```
**Clean up tasks:**
[] Clean up heartbeat table(s).
```
sudo db-mysql db2140 heartbeat -e "delete from heartbeat where file like 'db2110%';"
```
[] change events for query killer:
```
events_coredb_master.sql on the new primary db2140
events_coredb_slave.sql on the new slave db2110
```
[] Update candidate primary dbctl and orchestrator notes
```
sudo dbctl instance db2110 set-candidate-master --section s4 true
sudo dbctl instance db2140 set-candidate-master --section s4 false
(dborch1001): sudo orchestrator-client -c untag -i db2140 --tag name=candidate
(dborch1001): sudo orchestrator-client -c tag -i db2110 --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 = 's4';"
```
[] (If needed): Depool db2110 for maintenance.
```
sudo dbctl instance db2110 depool
sudo dbctl config commit -m "Depool db2110 T328022"
```
[] Change db2110 weight to mimic the previous weight db2140:
```
sudo dbctl instance db2110 edit
```
[] Apply outstanding schema changes to db2110 (if any)
[] Update/resolve this ticket.