**When:** During a pre-defined DBA maintenance windows
**Prerequisites:** https://wikitech.wikimedia.org/wiki/MariaDB/Primary_switchover
[x] Team calendar invite
**Affected wikis:**: https://noc.wikimedia.org/conf/highlight.php?file=dblists/s1.dblist
**Checklist:**
NEW primary: db2103
OLD primary: db2112
[x] Check configuration differences between new and old primary:
```
sudo pt-config-diff --defaults-file /root/.my.cnf h=db2112.codfw.wmnet h=db2103.codfw.wmnet
```
```
20 config differences
Variable db2112 db2103
========================= ========================= =========================
general_log_file db2112.log db2103.log
gtid_binlog_pos 171970572-171970572-39... 171970572-171970572-39...
gtid_binlog_state 171970572-171970572-39... 171970572-171970572-39...
gtid_current_pos 0-171970637-5484646134... 0-171970637-5484646134...
gtid_domain_id 180363268 180355190
gtid_slave_pos 0-171970637-5484646134... 0-171970637-5484646134...
hostname db2112 db2103
innodb_version 10.4.25 10.4.26
log_bin_basename /srv/sqldata/db2112-bin /srv/sqldata/db2103-bin
log_bin_index /srv/sqldata/db2112-bi... /srv/sqldata/db2103-bi...
pid_file /srv/sqldata/db2112.pid /srv/sqldata/db2103.pid
read_only OFF ON
report_host db2112.codfw.wmnet db2103.codfw.wmnet
rpl_semi_sync_master_e... ON OFF
rpl_semi_sync_slave_en... OFF ON
server_id 180363268 180355190
slow_query_log_file db2112-slow.log db2103-slow.log
version 10.4.25-MariaDB-log 10.4.26-MariaDB-log
version_source_revision 23ddc3518f999e003d54f7... 65e8506ca9d03967191b6e...
wsrep_node_name db2112 db2103
```
**Failover prep:**
[x] Silence alerts on all hosts:
```
sudo cookbook sre.hosts.downtime --hours 2 -r "Primary switchover s1 T350142" 'A:db-section-s1'
```
[] Set NEW primary with weight 0 (and depool it from API or vslow/dump groups if it is present).
:warning: Take note of the weight to restore it on the old primary later.
```
sudo dbctl instance db2103 set-weight 0
sudo dbctl config commit -m "Set db2103 with weight 0 T350142"
```
[] Topology changes, move all replicas under NEW primary
```
sudo db-switchover --timeout=25 --only-slave-move db2112 db2103
```
[] Disable puppet on both nodes
```
sudo cumin 'db2112* or db2103*' 'disable-puppet "primary switchover T350142"'
```
[] Merge gerrit puppet change to promote NEW primary:
```
sudo puppet-merge
```
**Failover:**
[] Log the failover:
```
!log Starting s1 codfw failover from db2112 to db2103 - T350142
```
[] Set section read-only:
```
sudo dbctl --scope codfw section s1 ro "Maintenance until 06:15 UTC - T350142"
sudo dbctl config commit -m "Set s1 codfw as read-only for maintenance - T350142"
```
[] Check s1 is indeed read-only
```
select @@read_only;
```
[] Switch primaries:
```
sudo db-switchover --skip-slave-move db2112 db2103
```
:warning: Retrieve the 2 `curl` commands that the script returns
```
echo "===== db2112 (OLD)"; sudo db-mysql db2112 -e 'show slave status\G'
echo "===== db2103 (NEW)"; sudo db-mysql db2103 -e 'show slave status\G'
```
[] Promote NEW primary in dbctl, and remove read-only
```
sudo dbctl --scope codfw section s1 set-master db2103
sudo dbctl --scope codfw section s1 rw
sudo dbctl config commit -m "Promote db2103 to s1 primary and set section read-write T350142"
```
[] Restart puppet on both hosts:
```
sudo cumin 'db2112* or db2103*' 'run-puppet-agent -e "primary switchover T350142"'
```
**Clean up tasks:**
[] Clean up heartbeat table(s).
```
sudo db-mysql db2103 heartbeat -e "delete from heartbeat where file like 'db2112%';"
```
[] change events for query killer:
```
events_coredb_master.sql on the new primary db2103
events_coredb_slave.sql on the new slave db2112
```
[] Update DNS:
```
ssh ns0.wikimedia.org
sudo authdns-update
```
[] Update candidate primary dbctl and orchestrator notes
```
sudo dbctl instance db2112 set-candidate-master --section s1 true
sudo dbctl instance db2103 set-candidate-master --section s1 false
(dborch1001): sudo orchestrator-client -c untag -i db2103 --tag name=candidate
(dborch1001): sudo orchestrator-client -c tag -i db2112 --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 = 's1';"
```
[] (If needed): Depool db2112 for maintenance.
```
sudo dbctl instance db2112 depool
sudo dbctl config commit -m "Depool db2112 T350142"
```
[] Change db2112 weight to mimic the previous weight db2103:
```
sudo dbctl instance db2112 edit
```
[] Apply outstanding schema changes to db2112 (if any)
[] Update/resolve this ticket.