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/s6.dblist
Checklist:
NEW primary: db1231
OLD primary: db1173
- Check configuration differences between new and old primary:
sudo pt-config-diff --defaults-file /root/.my.cnf h=db1173.eqiad.wmnet h=db1231.eqiad.wmnet
Failover prep:
- Silence alerts on all hosts:
sudo cookbook sre.hosts.downtime --hours 1 -r "Primary switchover s6 T364067" 'A:db-section-s6'
- Set NEW primary with weight 0
sudo dbctl instance db1231 set-weight 0 sudo dbctl config commit -m "Set db1231 with weight 0 T364067"
- Depool NEW from any specific group (API, vslow, dump) if present.
sudo dbctl instance db1231 edit # If some changes were made: sudo dbctl config commit -m "Remove db1231 from API/vslow/dump T364067"
- Topology changes, move all replicas under NEW primary
sudo db-switchover --timeout=25 --only-slave-move db1173 db1231
- Disable puppet on both nodes
sudo cumin 'db1173* or db1231*' 'disable-puppet "primary switchover T364067"'
- Merge gerrit puppet change to promote NEW primary: https://gerrit.wikimedia.org/r/1025916
Failover:
- Log the failover:
!log Starting s6 eqiad failover from db1173 to db1231 - T364067
- Set section read-only:
sudo dbctl --scope eqiad section s6 ro "Maintenance until 06:15 UTC - T364067" sudo dbctl --scope codfw section s6 ro "Maintenance until 06:15 UTC - T364067" sudo dbctl config commit -m "Set s6 eqiad as read-only for maintenance - T364067"
- Check s6 is indeed read-only
- Switch primaries:
sudo db-switchover --skip-slave-move db1173 db1231 echo "===== db1173 (OLD)"; sudo db-mysql db1173 -e 'show slave status\G' echo "===== db1231 (NEW)"; sudo db-mysql db1231 -e 'show slave status\G'
- Promote NEW primary in dbctl, and remove read-only
sudo dbctl --scope eqiad section s6 set-master db1231 sudo dbctl --scope eqiad section s6 rw sudo dbctl --scope codfw section s6 rw sudo dbctl config commit -m "Promote db1231 to s6 primary and set section read-write T364067"
- Restart puppet on both hosts:
sudo cumin 'db1173* or db1231*' 'run-puppet-agent -e "primary switchover T364067"'
Clean up tasks:
- Clean up heartbeat table(s).
sudo db-mysql db1231 heartbeat -e "delete from heartbeat where file like 'db1173%';"
- change events for query killer:
events_coredb_master.sql on the new primary db1231 events_coredb_slave.sql on the new slave db1173
- Update DNS: https://gerrit.wikimedia.org/r/1025917
- Update candidate primary dbctl and orchestrator notes
sudo dbctl instance db1173 set-candidate-master --section s6 true sudo dbctl instance db1231 set-candidate-master --section s6 false (dborch1001): sudo orchestrator-client -c untag -i db1231 --tag name=candidate (dborch1001): sudo orchestrator-client -c tag -i db1173 --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 = 's6';"
- (If needed): Depool db1173 for maintenance.
sudo dbctl instance db1173 depool sudo dbctl config commit -m "Depool db1173 T364067"
- Change db1173 weight to mimic the previous weight db1231:
sudo dbctl instance db1173 edit
- Apply outstanding schema changes to db1173 (if any)
- Update/resolve this ticket.