When: During a pre-defined DBA maintenance windows
Prerequisites: https://wikitech.wikimedia.org/wiki/MariaDB/Primary_switchover
- Team calendar invite
Affected wikis:: https://noc.wikimedia.org/conf/highlight.php?file=dblists/s7.dblist
Checklist:
NEW primary: db2121
OLD primary: db2118
- Check configuration differences between new and old primary:
sudo pt-config-diff --defaults-file /root/.my.cnf h=db2118.codfw.wmnet h=db2121.codfw.wmnet
Failover prep:
- Silence alerts on all hosts:
sudo cookbook sre.hosts.downtime --hours 1 -r "Primary switchover s7 T358423" 'A:db-section-s7'
- Set NEW primary with weight 0 (and depool it from API or vslow/dump groups if it is present).
sudo dbctl instance db2121 set-weight 0 sudo dbctl config commit -m "Set db2121 with weight 0 T358423"
- Topology changes, move all replicas under NEW primary
sudo db-switchover --timeout=25 --only-slave-move db2118 db2121
- Disable puppet on both nodes
sudo cumin 'db2118* or db2121*' 'disable-puppet "primary switchover T358423"'
- Merge gerrit puppet change to promote NEW primary: https://gerrit.wikimedia.org/r/1006108
Failover:
- Log the failover:
!log Starting s7 codfw failover from db2118 to db2121 - T358423
- Set section read-only:
sudo dbctl --scope eqiad section s7 ro "Maintenance until 06:15 UTC - T358423" sudo dbctl --scope codfw section s7 ro "Maintenance until 06:15 UTC - T358423" sudo dbctl config commit -m "Set s7 codfw as read-only for maintenance - T358423"
- Check s7 is indeed read-only
- Switch primaries:
sudo db-switchover --skip-slave-move db2118 db2121 echo "===== db2118 (OLD)"; sudo db-mysql db2118 -e 'show slave status\G' echo "===== db2121 (NEW)"; sudo db-mysql db2121 -e 'show slave status\G'
- Promote NEW primary in dbctl, and remove read-only
sudo dbctl --scope codfw section s7 set-master db2121 sudo dbctl --scope eqiad section s7 rw sudo dbctl --scope codfw section s7 rw sudo dbctl config commit -m "Promote db2121 to s7 primary and set section read-write T358423"
- Restart puppet on both hosts:
sudo cumin 'db2118* or db2121*' 'run-puppet-agent -e "primary switchover T358423"'
Clean up tasks:
- Clean up heartbeat table(s).
sudo db-mysql db2121 heartbeat -e "delete from heartbeat where file like 'db2118%';"
- change events for query killer:
events_coredb_master.sql on the new primary db2121 events_coredb_slave.sql on the new slave db2118
- Update DNS: https://gerrit.wikimedia.org/r/1006109
- Update candidate primary dbctl and orchestrator notes
sudo dbctl instance db2118 set-candidate-master --section s7 true sudo dbctl instance db2121 set-candidate-master --section s7 false (dborch1001): sudo orchestrator-client -c untag -i db2121 --tag name=candidate (dborch1001): sudo orchestrator-client -c tag -i db2118 --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 = 's7';"
- (If needed): Depool db2118 for maintenance.
sudo dbctl instance db2118 depool sudo dbctl config commit -m "Depool db2118 T358423"
- Change db2118 weight to mimic the previous weight db2121:
sudo dbctl instance db2118 edit
- Update/resolve this ticket.