**When:** Anytime - no in use
** Prerequisites **: https://wikitech.wikimedia.org/wiki/MariaDB/Primary_switchover
**Checklist:**
NEW primary: es2020
OLD primary: es2021
[x] Check configuration differences between new and old primary:
```
sudo pt-config-diff --defaults-file /root/.my.cnf h=es2021.codfw.wmnet h=es2020.codfw.wmnet
```
**Failover prep:**
[x] Silence alerts on all hosts:
```
sudo cookbook sre.hosts.downtime --hours 1 -r "Primary switchover es4 T317507" 'A:db-section-es4'
```
[x] Set NEW primary with weight 0 (and depool it from API or vslow/dump groups if it is present).
```
sudo dbctl instance es2020 set-weight 0
sudo dbctl config commit -m "Set es2020 with weight 0 T317507"
```
[x] Topology changes, move all replicas under NEW primary
```
sudo db-switchover --read-only-master --replicating-master --timeout=25 --only-slave-move es2021 es2020
```
[x] Disable puppet on both nodes
```
sudo cumin 'es2021* or es2020*' 'disable-puppet "primary switchover T317507"'
```
[x] Merge gerrit puppet change to promote NEW primary: https://gerrit.wikimedia.org/r/c/operations/puppet/+/831464/
**Failover:**
[x] Log the failover:
```
!log Starting es4 codfw failover from es2021 to es2020 - T317507
```
[x] Switch primaries:
```
sudo db-switchover --read-only-master --replicating-master --skip-slave-move es2021 es2020
echo "===== es2021 (OLD)"; sudo db-mysql es2021 -e 'show slave status\G'
echo "===== es2020 (NEW)"; sudo db-mysql es2020 -e 'show slave status\G'
```
[x] Promote NEW primary in dbctl, and remove read-only
```
sudo dbctl --scope codfw section es4 set-master es2020
sudo dbctl --scope codfw section es4 rw
sudo dbctl config commit -m "Promote es2020 to es4 primary and set section read-write T317507"
```
[x] Restart puppet on both hosts:
```
sudo cumin 'es2021* or es2020*' 'run-puppet-agent -e "primary switchover T317507"'
```
**Clean up tasks:**
[x] Clean up heartbeat table(s).
```
sudo db-mysql es2020 heartbeat -e "delete from heartbeat where file like 'es2021%';"
```
[x] change events for query killer:
```
events_coredb_master.sql on the new primary es2020
events_coredb_slave.sql on the new slave es2021
```
[x] Update candidate primary dbctl and orchestrator notes
```
sudo dbctl instance es2021 set-candidate-master --section es4 true
sudo dbctl instance es2020 set-candidate-master --section es4 false
(dborch1001): sudo orchestrator-client -c untag -i es2020 --tag name=candidate
(dborch1001): sudo orchestrator-client -c tag -i es2021 --tag name=candidate
```
[x] 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 = 'es4';"
```
[x] (If needed): Depool es2021 for maintenance.
```
sudo dbctl instance es2021 depool
sudo dbctl config commit -m "Depool es2021 T317507"
```
[x] Change es2021 weight to mimic the previous weight es2020:
```
sudo dbctl instance es2021 edit
```
[] Update/resolve this ticket.