When: Anytime, writes will be disabled
- Prerequisites **: https://wikitech.wikimedia.org/wiki/MariaDB/Primary_switchover
Checklist:
NEW primary: es2020
OLD primary: es2021
- 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
- Disable writes in es4 by merging: https://gerrit.wikimedia.org/r/c/operations/mediawiki-config/+/1004668
- Check es4 is indeed read-only
Failover prep:
- Silence alerts on all hosts:
sudo cookbook sre.hosts.downtime --hours 1 -r "Primary switchover es4 T356372" 'A:db-section-es4'
- 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 T356372"
- Topology changes, move all replicas under NEW primary
sudo db-switchover --timeout=25 --only-slave-move es2021 es2020
- Disable puppet on both nodes
sudo cumin 'es2020* or es2021*' 'disable-puppet "primary switchover T356372"'
- Merge gerrit puppet change to promote NEW primary: https://gerrit.wikimedia.org/r/c/operations/puppet/+/1004669
Failover:
- Log the failover:
!log Starting es4 codfw failover from es2021 to es2020 - T356372
- Switch primaries:
sudo db-switchover --skip-slave-move es2021 es2020 echo "===== es1020 (OLD)"; sudo db-mysql es2021 -e 'show slave status\G' echo "===== es1021 (NEW)"; sudo db-mysql es2020 -e 'show slave status\G'
- Promote NEW primary in dbctl, and remove read-only
sudo dbctl --scope codfw section es4 set-master es2020 sudo dbctl config commit -m "Promote es2020 to es4 primary T356372"
- Restart puppet on both hosts:
sudo cumin 'es2021* or es2020*' 'run-puppet-agent -e "primary switchover T356372"'
Clean up tasks:
- Clean up heartbeat table(s).
sudo db-mysql es2020 heartbeat -e "delete from heartbeat where file like 'es2021%';"
- change events for query killer:
events_coredb_master.sql on the new primary es2020 events_coredb_slave.sql on the new slave es2021
- Update DNS: https://gerrit.wikimedia.org/r/1004670
- 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
- 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 = 'es4';"
- (If needed): Depool es2021 for maintenance.
sudo dbctl instance es2021 depool sudo dbctl config commit -m "Depool es2021 T356372"
- Change es2021 weight to mimic the previous weight es2020:
sudo dbctl instance es2021 edit
- Enable writes in es4 by merging the revert patch: https://gerrit.wikimedia.org/r/c/operations/mediawiki-config/+/1004715
- Update/resolve this ticket.