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/s5.dblist
Checklist:
NEW primary: db1210
OLD primary: db1230
- Check configuration differences between new and old primary:
sudo pt-config-diff --defaults-file /root/.my.cnf h=db1230.eqiad.wmnet h=db1210.eqiad.wmnet
Failover prep:
- Silence alerts on all hosts:
sudo cookbook sre.hosts.downtime --hours 1 -r "Primary switchover s5 T398593" 'A:db-section-s5'
- Set NEW primary with weight 0
sudo dbctl instance db1210 set-weight 0 sudo dbctl config commit -m "Set db1210 with weight 0 T398593"
- Depool NEW from any specific group (API, vslow, dump) if present.
sudo dbctl instance db1210 edit # If some changes were made: sudo dbctl config commit -m "Remove db1210 from API/vslow/dump T398593"
- Topology changes, move all replicas under NEW primary
sudo db-switchover --timeout=25 --only-slave-move db1230 db1210
- Disable puppet on both nodes
sudo cumin 'db1230* or db1210*' 'disable-puppet "primary switchover T398593"'
- Merge gerrit puppet change to promote NEW primary: FIXME
Failover:
- Log the failover:
!log Starting s5 eqiad failover from db1230 to db1210 - T398593
- Set section read-only:
sudo dbctl --scope eqiad section s5 ro "Maintenance until 06:15 UTC - T398593" sudo dbctl --scope codfw section s5 ro "Maintenance until 06:15 UTC - T398593" sudo dbctl config commit -m "Set s5 eqiad as read-only for maintenance - T398593"
- Check s5 is indeed read-only
- Switch primaries:
sudo db-switchover --skip-slave-move db1230 db1210 echo "===== db1230 (OLD)"; sudo db-mysql db1230 -e 'show slave status\G' echo "===== db1210 (NEW)"; sudo db-mysql db1210 -e 'show slave status\G'
- Promote NEW primary in dbctl, and remove read-only
sudo dbctl --scope eqiad section s5 set-master db1210 sudo dbctl --scope eqiad section s5 rw sudo dbctl --scope codfw section s5 rw sudo dbctl config commit -m "Promote db1210 to s5 primary and set section read-write T398593"
- Clean up heartbeat table(s).
sudo db-mysql db1210 heartbeat -e "delete from heartbeat where file like 'db1230%';"
- Restart puppet on both hosts:
sudo cumin 'db1230* or db1210*' 'run-puppet-agent -e "primary switchover T398593"'
Clean up tasks:
- change events for query killer:
curl -sS 'https://gerrit.wikimedia.org/r/plugins/gitiles/operations/software/+/refs/heads/master/dbtools/events_coredb_master.sql?format=TEXT' | base64 -d | sudo db-mysql db1210 curl -sS 'https://gerrit.wikimedia.org/r/plugins/gitiles/operations/software/+/refs/heads/master/dbtools/events_coredb_slave.sql?format=TEXT' | base64 -d | sudo db-mysql db1230
- Update DNS: FIXME
- Update candidate primary dbctl and orchestrator notes
sudo dbctl instance db1230 set-candidate-master --section s5 true sudo dbctl instance db1210 set-candidate-master --section s5 false sudo cumin 'dborch*' 'orchestrator-client -c untag -i db1210 --tag name=candidate' sudo cumin 'dborch*' 'orchestrator-client -c tag -i db1230 --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 = 's5';"
- (If needed): Depool db1230 for maintenance.
sudo dbctl instance db1230 depool sudo dbctl config commit -m "Depool db1230 T398593"
- Change db1230 weight to mimic the previous weight db1210 (main/api/vslow/dumps):
sudo dbctl instance db1230 edit
- Apply outstanding schema changes to db1230 (if any)
- Update/resolve this ticket.