When: During a pre-defined DBA maintenance windows
Prerequisites: https://wikitech.wikimedia.org/wiki/MariaDB/Primary_switchover
- Team calendar invite
Affected wikis:: TO-DO
Checklist:
NEW primary: db2196
OLD primary: db2115
- Check configuration differences between new and old primary:
sudo pt-config-diff --defaults-file /root/.my.cnf h=db2115.codfw.wmnet h=db2196.codfw.wmnet
Failover prep:
- Silence alerts on all hosts:
sudo cookbook sre.hosts.downtime --hours 1 -r "Primary switchover x1 T359919" 'A:db-section-x1'
- Set NEW primary with weight 0 (and depool it from API or vslow/dump groups if it is present).
sudo dbctl instance db2196 set-weight 0 sudo dbctl config commit -m "Set db2196 with weight 0 T359919"
- Topology changes, move all replicas under NEW primary
sudo db-switchover --timeout=25 --only-slave-move db2115 db2196
- Disable puppet on both nodes
sudo cumin 'db2115* or db2196*' 'disable-puppet "primary switchover T359919"'
- Merge gerrit puppet change to promote NEW primary: FIXME
Failover:
- Log the failover:
!log Starting x1 codfw failover from db2115 to db2196 - T359919
- Set section read-only:
sudo dbctl --scope eqiad section x1 ro "Maintenance until 06:15 UTC - T359919" sudo dbctl --scope codfw section x1 ro "Maintenance until 06:15 UTC - T359919" sudo dbctl config commit -m "Set x1 codfw as read-only for maintenance - T359919"
- Check x1 is indeed read-only
- Switch primaries:
sudo db-switchover --skip-slave-move db2115 db2196 echo "===== db2115 (OLD)"; sudo db-mysql db2115 -e 'show slave status\G' echo "===== db2196 (NEW)"; sudo db-mysql db2196 -e 'show slave status\G'
- Promote NEW primary in dbctl, and remove read-only
sudo dbctl --scope codfw section x1 set-master db2196 sudo dbctl --scope eqiad section x1 rw sudo dbctl --scope codfw section x1 rw sudo dbctl config commit -m "Promote db2196 to x1 primary and set section read-write T359919"
- Restart puppet on both hosts:
sudo cumin 'db2115* or db2196*' 'run-puppet-agent -e "primary switchover T359919"'
Clean up tasks:
- Clean up heartbeat table(s).
sudo db-mysql db2196 heartbeat -e "delete from heartbeat where file like 'db2115%';"
- change events for query killer:
events_coredb_master.sql on the new primary db2196 events_coredb_slave.sql on the new slave db2115
- Update DNS: FIXME
- Update candidate primary dbctl and orchestrator notes
sudo dbctl instance db2115 set-candidate-master --section x1 true sudo dbctl instance db2196 set-candidate-master --section x1 false (dborch1001): sudo orchestrator-client -c untag -i db2196 --tag name=candidate (dborch1001): sudo orchestrator-client -c tag -i db2115 --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 = 'x1';"
- (If needed): Depool db2115 for maintenance.
sudo dbctl instance db2115 depool sudo dbctl config commit -m "Depool db2115 T359919"
- Change db2115 weight to mimic the previous weight db2196:
sudo dbctl instance db2115 edit
- Apply outstanding schema changes to db2115 (if any)
- Update/resolve this ticket.