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/s8.dblist
Checklist:
NEW primary: db2165
OLD primary: db2161
- Check configuration differences between new and old primary:
sudo pt-config-diff --defaults-file /root/.my.cnf h=db2161.codfw.wmnet h=db2165.codfw.wmnet
Failover prep:
- Silence alerts on all hosts:
sudo cookbook sre.hosts.downtime --hours 1 -r "Primary switchover s8 T349053" 'A:db-section-s8'
- Set NEW primary with weight 0 (and depool it from API or vslow/dump groups if it is present).
sudo dbctl instance db2165 set-weight 0 sudo dbctl config commit -m "Set db2165 with weight 0 T349053"
- Topology changes, move all replicas under NEW primary
sudo db-switchover --timeout=25 --only-slave-move db2161 db2165
- Disable puppet on both nodes
sudo cumin 'db2161* or db2165*' 'disable-puppet "primary switchover T349053"'
- Merge gerrit puppet change to promote NEW primary: https://gerrit.wikimedia.org/r/c/operations/puppet/+/965579/
Failover:
- Log the failover:
!log Starting s8 codfw failover from db2161 to db2165 - T349053
- Set section read-only:
sudo dbctl --scope codfw section s8 ro "Maintenance until 06:15 UTC - T349053" sudo dbctl config commit -m "Set s8 codfw as read-only for maintenance - T349053"
- Check s8 is indeed read-only
- Switch primaries:
sudo db-switchover --skip-slave-move db2161 db2165 echo "===== db2161 (OLD)"; sudo db-mysql db2161 -e 'show slave status\G' echo "===== db2165 (NEW)"; sudo db-mysql db2165 -e 'show slave status\G'
- Promote NEW primary in dbctl, and remove read-only
sudo dbctl --scope codfw section s8 set-master db2165 sudo dbctl --scope codfw section s8 rw sudo dbctl config commit -m "Promote db2165 to s8 primary and set section read-write T349053"
- Restart puppet on both hosts:
sudo cumin 'db2161* or db2165*' 'run-puppet-agent -e "primary switchover T349053"'
Clean up tasks:
- Clean up heartbeat table(s).
sudo db-mysql db2165 heartbeat -e "delete from heartbeat where file like 'db2161%';"
- change events for query killer:
events_coredb_master.sql on the new primary db2165 events_coredb_slave.sql on the new slave db2161
- Update DNS: https://gerrit.wikimedia.org/r/c/operations/dns/+/965580/
- Update candidate primary dbctl and orchestrator notes
sudo dbctl instance db2161 set-candidate-master --section s8 true sudo dbctl instance db2165 set-candidate-master --section s8 false (dborch1001): sudo orchestrator-client -c untag -i db2165 --tag name=candidate (dborch1001): sudo orchestrator-client -c tag -i db2161 --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 = 's8';"
- (If needed): Depool db2161 for maintenance.
sudo dbctl instance db2161 depool sudo dbctl config commit -m "Depool db2161 T349053"
- Change db2161 weight to mimic the previous weight db2165:
sudo dbctl instance db2161 edit
- Update/resolve this ticket.