**When:** During a pre-defined DBA maintenance windows
**Affected wikis:**: https://noc.wikimedia.org/conf/highlight.php?file=dblists/s3.dblist
**Checklist:**
NEW primary: db1223
OLD primary: db1189
[] Check configuration differences between new and old primary:
```
sudo pt-config-diff --defaults-file /root/.my.cnf h=db1189.eqiad.wmnet h=db1223.eqiad.wmnet
```
**Failover prep:**
[] Silence alerts on all hosts:
```
sudo cookbook sre.hosts.downtime --hours 1 -r "Primary switchover s3 TICKID" 'A:db-section-s3'
```
[] Set NEW primary with weight 0
```
sudo dbctl instance db1223 set-weight 0
sudo dbctl config commit -m "Set db1223 with weight 0 TICKID"
```
[] Depool NEW from any specific group (API, vslow, dump) if present.
```
sudo dbctl instance db1223 edit
# If some changes were made:
sudo dbctl config commit -m "Remove db1223 from API/vslow/dump TICKID"
```
[] Topology changes, move all replicas under NEW primary
```
sudo db-switchover --timeout=25 --replicating-master --read-only-master --only-slave-move db1189 db1223
```
[] Disable puppet on both nodes
```
sudo cumin 'db1189* or db1223*' 'disable-puppet "primary switchover TICKID"'
```
[] Merge gerrit puppet change to promote NEW primary: FIXME
**Failover:**
[] Log the failover:
```
!log Starting s3 eqiad failover from db1189 to db1223 - TICKID
```
[] Switch primaries:
```
sudo db-switchover --replicating-master --read-only-master --skip-slave-move db1189 db1223
echo "===== db1189 (OLD)"; sudo db-mysql db1189 -e 'show slave status\G'
echo "===== db1223 (NEW)"; sudo db-mysql db1223 -e 'show slave status\G'
```
[] Promote NEW primary in dbctl
```
sudo dbctl --scope eqiad section s3 set-master db1223
sudo dbctl config commit -m "Promote db1223 to s3 primary TICKID"
```
[] Clean up heartbeat table(s).
```
sudo db-mysql db1223 heartbeat -e "delete from heartbeat where file like 'db1189%';"
```
[] Restart puppet on both hosts:
```
sudo cumin 'db1189* or db1223*' 'run-puppet-agent -e "primary switchover TICKID"'
```
**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 db1223
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 db1189
```
[] Update candidate primary dbctl and orchestrator notes
```
sudo dbctl instance db1189 set-candidate-master --section s3 true
sudo dbctl instance db1223 set-candidate-master --section s3 false
sudo cumin 'dborch*' 'orchestrator-client -c untag -i db1223 --tag name=candidate'
sudo cumin 'dborch*' 'orchestrator-client -c tag -i db1189 --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 = 's3';"
```
[] (If needed): Depool db1189 for maintenance.
```
sudo dbctl instance db1189 depool
sudo dbctl config commit -m "Depool db1189 TICKID"
```
[] Change db1189 weight to mimic the previous weight db1223:
```
sudo dbctl instance db1189 edit
```
[] Apply outstanding schema changes to db1189 (if any)
[] Update/resolve this ticket.