**When:** During a pre-defined DBA maintenance windows
**Affected wikis:**: https://noc.wikimedia.org/conf/highlight.php?file=dblists/s4.dblist
**Checklist:**
NEW primary: db1160
OLD primary: db1138
[x] Check configuration differences between new and old primary:
```
$ sudo pt-config-diff --defaults-file /root/.my.cnf h=db1138.eqiad.wmnet h=db1160.eqiad.wmnet
16 config differences
Variable db1138 db1160
========================= ========================= =========================
general_log_file db1138.log db1160.log
gtid_binlog_pos 171966513-171966513-28... 171966513-171966513-28...
gtid_binlog_state 171966513-171966513-28... 171966513-171966513-28...
gtid_current_pos 0-180359175-3368394787... 0-180359175-3368394787...
gtid_domain_id 171978876 171966513
gtid_slave_pos 0-180359175-3368394787... 0-180359175-3368394787...
hostname db1138 db1160
log_bin_basename /srv/sqldata/db1138-bin /srv/sqldata/db1160-bin
log_bin_index /srv/sqldata/db1138-bi... /srv/sqldata/db1160-bi...
pid_file /srv/sqldata/db1138.pid /srv/sqldata/db1160.pid
report_host db1138.eqiad.wmnet db1160.eqiad.wmnet
rpl_semi_sync_master_e... ON OFF
rpl_semi_sync_slave_en... OFF ON
server_id 171978876 171966513
slow_query_log_file db1138-slow.log db1160-slow.log
wsrep_node_name db1138 db1160
```
**Failover prep:**
[x] Silence alerts on all hosts:
```
sudo cookbook sre.hosts.downtime --hours 1 -r "Primary switchover s4 T351184" 'A:db-section-s4'
```
[x] Set NEW primary with weight 0 (and depool it from API or vslow/dump groups if it is present).
```
sudo dbctl instance db1160 set-weight 0
sudo dbctl config commit -m "Set db1160 with weight 0 T351184"
```
[x] Topology changes, move all replicas under NEW primary
```
sudo db-switchover --timeout=25 --replicating-master --read-only-master --only-slave-move db1138 db1160
```
[] Disable puppet on both nodes
```
sudo cumin 'db1138* or db1160*' 'disable-puppet "primary switchover T351184"'
```
[] Merge gerrit puppet change to promote NEW primary: FIXME
**Failover:**
[] Log the failover:
```
!log Starting s4 eqiad failover from db1138 to db1160 - T351184
```
[] Switch primaries:
```
sudo db-switchover --replicating-master --read-only-master --skip-slave-move db1138 db1160
echo "===== db1138 (OLD)"; sudo db-mysql db1138 -e 'show slave status\G'
echo "===== db1160 (NEW)"; sudo db-mysql db1160 -e 'show slave status\G'
```
[] Promote NEW primary in dbctl
```
sudo dbctl --scope eqiad section s4 set-master db1160
sudo dbctl config commit -m "Promote db1160 to s4 primary T351184"
```
[] Restart puppet on both hosts:
```
sudo cumin 'db1138* or db1160*' 'run-puppet-agent -e "primary switchover T351184"'
```
**Clean up tasks:**
[] Clean up heartbeat table(s).
```
sudo db-mysql db1160 heartbeat -e "delete from heartbeat where file like 'db1138%';"
```
[] change events for query killer:
```
events_coredb_master.sql on the new primary db1160
events_coredb_slave.sql on the new slave db1138
```
[] Update candidate primary dbctl and orchestrator notes
```
sudo dbctl instance db1138 set-candidate-master --section s4 true
sudo dbctl instance db1160 set-candidate-master --section s4 false
(dborch1001): sudo orchestrator-client -c untag -i db1160 --tag name=candidate
(dborch1001): sudo orchestrator-client -c tag -i db1138 --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 = 's4';"
```
[] (If needed): Depool db1138 for maintenance.
```
sudo dbctl instance db1138 depool
sudo dbctl config commit -m "Depool db1138 T351184"
```
[] Change db1138 weight to mimic the previous weight db1160:
```
sudo dbctl instance db1138 edit
```
[] Apply outstanding schema changes to db1138 (if any)
[] Update/resolve this ticket.