**When:** During a pre-defined DBA maintenance windows
**Prerequisites:** https://wikitech.wikimedia.org/wiki/MariaDB/Primary_switchover
[x] Team calendar invite
**Affected wikis:**: https://noc.wikimedia.org/conf/highlight.php?file=dblists/s6.dblist
**Checklist:**
NEW primary: db1231
OLD primary: db1173
[x] Check configuration differences between new and old primary:
```
sudo pt-config-diff --defaults-file /root/.my.cnf h=db1173.eqiad.wmnet h=db1231.eqiad.wmnet
```
**Failover prep:**
[] Silence alerts on all hosts:
```
sudo cookbook sre.hosts.downtime --hours 1 -r "Primary switchover s6 T364067" 'A:db-section-s6'
```
[] Set NEW primary with weight 0
```
sudo dbctl instance db1231 set-weight 0
sudo dbctl config commit -m "Set db1231 with weight 0 T364067"
```
[] Depool NEW from any specific group (API, vslow, dump) if present.
```
sudo dbctl instance db1231 edit
# If some changes were made:
sudo dbctl config commit -m "Remove db1231 from API/vslow/dump T364067"
```
[] Topology changes, move all replicas under NEW primary
```
sudo db-switchover --timeout=25 --only-slave-move db1173 db1231
```
[] Disable puppet on both nodes
```
sudo cumin 'db1173* or db1231*' 'disable-puppet "primary switchover T364067"'
```
[] Merge gerrit puppet change to promote NEW primary: https://gerrit.wikimedia.org/r/1025916
**Failover:**
[] Log the failover:
```
!log Starting s6 eqiad failover from db1173 to db1231 - T364067
```
[] Set section read-only:
```
sudo dbctl --scope eqiad section s6 ro "Maintenance until 06:15 UTC - T364067"
sudo dbctl --scope codfw section s6 ro "Maintenance until 06:15 UTC - T364067"
sudo dbctl config commit -m "Set s6 eqiad as read-only for maintenance - T364067"
```
[] Check s6 is indeed read-only
[] Switch primaries:
```
sudo db-switchover --skip-slave-move db1173 db1231
echo "===== db1173 (OLD)"; sudo db-mysql db1173 -e 'show slave status\G'
echo "===== db1231 (NEW)"; sudo db-mysql db1231 -e 'show slave status\G'
```
[] Promote NEW primary in dbctl, and remove read-only
```
sudo dbctl --scope eqiad section s6 set-master db1231
sudo dbctl --scope eqiad section s6 rw
sudo dbctl --scope codfw section s6 rw
sudo dbctl config commit -m "Promote db1231 to s6 primary and set section read-write T364067"
```
[] Restart puppet on both hosts:
```
sudo cumin 'db1173* or db1231*' 'run-puppet-agent -e "primary switchover T364067"'
```
**Clean up tasks:**
[] Clean up heartbeat table(s).
```
sudo db-mysql db1231 heartbeat -e "delete from heartbeat where file like 'db1173%';"
```
[] change events for query killer:
```
events_coredb_master.sql on the new primary db1231
events_coredb_slave.sql on the new slave db1173
```
[] Update DNS: https://gerrit.wikimedia.org/r/1025917
[] Update candidate primary dbctl and orchestrator notes
```
sudo dbctl instance db1173 set-candidate-master --section s6 true
sudo dbctl instance db1231 set-candidate-master --section s6 false
(dborch1001): sudo orchestrator-client -c untag -i db1231 --tag name=candidate
(dborch1001): sudo orchestrator-client -c tag -i db1173 --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 = 's6';"
```
[] (If needed): Depool db1173 for maintenance.
```
sudo dbctl instance db1173 depool
sudo dbctl config commit -m "Depool db1173 T364067"
```
[] Change db1173 weight to mimic the previous weight db1231:
```
sudo dbctl instance db1173 edit
```
[] Apply outstanding schema changes to db1173 (if any)
[] Update/resolve this ticket.