**When:** Anytime, writes will be disabled
** Prerequisites **: https://wikitech.wikimedia.org/wiki/MariaDB/Primary_switchover
**Checklist:**
NEW primary: es1020
OLD primary: es1021
[x] Check configuration differences between new and old primary:
```
sudo pt-config-diff --defaults-file /root/.my.cnf h=es1021.eqiad.wmnet h=es1020.eqiad.wmnet
```
[x] Disable writes in es4 by merging: https://gerrit.wikimedia.org/r/c/operations/mediawiki-config/+/831511/
[] Check es4 is indeed read-only
**Failover prep:**
[x] Silence alerts on all hosts:
```
sudo cookbook sre.hosts.downtime --hours 1 -r "Primary switchover es4 T317522" '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 es1020 set-weight 0
sudo dbctl config commit -m "Set es1020 with weight 0 T317522"
```
[x] Topology changes, move all replicas under NEW primary
```
sudo db-switchover --timeout=25 --only-slave-move es1021 es1020
```
[x] Disable puppet on both nodes
```
sudo cumin 'es1021* or es1020*' 'disable-puppet "primary switchover T317522"'
```
[] Merge gerrit puppet change to promote NEW primary: https://gerrit.wikimedia.org/r/c/operations/puppet/+/831513/
**Failover:**
[] Log the failover:
```
!log Starting es4 eqiad failover from es1021 to es1020 - T317522
```
[] Switch primaries:
```
sudo db-switchover --skip-slave-move es1021 es1020
echo "===== es1021 (OLD)"; sudo db-mysql es1021 -e 'show slave status\G'
echo "===== es1020 (NEW)"; sudo db-mysql es1020 -e 'show slave status\G'
```
[] Promote NEW primary in dbctl, and remove read-only
```
sudo dbctl --scope eqiad section es4 set-master es1020
sudo dbctl config commit -m "Promote es1020 to es4 primary T317522"
```
[] Restart puppet on both hosts:
```
sudo cumin 'es1021* or es1020*' 'run-puppet-agent -e "primary switchover T317522"'
```
**Clean up tasks:**
[] Clean up heartbeat table(s).
```
sudo db-mysql es1020 heartbeat -e "delete from heartbeat where file like 'es1021%';"
```
[] change events for query killer:
```
events_coredb_master.sql on the new primary es1020
events_coredb_slave.sql on the new slave es1021
```
[] Update DNS: FIXME
[] Update candidate primary dbctl and orchestrator notes
```
sudo dbctl instance es1021 set-candidate-master --section es4 true
sudo dbctl instance es1020 set-candidate-master --section es4 false
(dborch1001): sudo orchestrator-client -c untag -i es1020 --tag name=candidate
(dborch1001): sudo orchestrator-client -c tag -i es1021 --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 = 'es4';"
```
[] (If needed): Depool es1021 for maintenance.
```
sudo dbctl instance es1021 depool
sudo dbctl config commit -m "Depool es1021 T317522"
```
[] Change es1021 weight to mimic the previous weight es1020:
```
sudo dbctl instance es1021 edit
```
[] Enable writes in es4 by reverting: TO-DO
[] Apply outstanding schema changes to es1021 (if any)
[] Update/resolve this ticket.