**When:** Anytime, writes will be disabled
**Prerequisites**: https://wikitech.wikimedia.org/wiki/MariaDB/Primary_switchover
**Checklist:**
NEW primary: es1038
OLD primary: es1037
[x] Check configuration differences between new and old primary:
```
$ sudo pt-config-diff --defaults-file /root/.my.cnf h=es1037.eqiad.wmnet h=es1038.eqiad.wmnet
15 config differences
Variable es1037 es1038
========================= ========================= =========================
general_log_file es1037.log es1038.log
gtid_domain_id 172006403 172007428
gtid_slave_pos 0-171966521-9791330871... 0-171966521-9791330871...
hostname es1037 es1038
log_bin_basename /srv/sqldata/es1037-bin /srv/sqldata/es1038-bin
log_bin_index /srv/sqldata/es1037-bi... /srv/sqldata/es1038-bi...
pid_file /srv/sqldata/es1037.pid /srv/sqldata/es1038.pid
read_only OFF ON
report_host es1037.eqiad.wmnet es1038.eqiad.wmnet
rpl_semi_sync_master_e... ON OFF
rpl_semi_sync_slave_en... OFF ON
server_id 172006403 172007428
slow_query_log_file es1037-slow.log es1038-slow.log
thread_pool_stall_limit 100 10
wsrep_node_name es1037 es1038
```
[x] Disable writes in es6 merging https://gerrit.wikimedia.org/r/c/operations/mediawiki-config/+/1049555 and deploying it:
(in deployment.eqiad.org):
```
scap backport 1049555
```
[x] Check es6 is indeed read-only
**Failover prep:**
[x] Silence alerts on all hosts:
```
sudo cookbook sre.hosts.downtime --hours 1 -r "Primary switchover es6 T368401" 'A:db-section-es6'
```
[x] Set NEW primary with weight 0 (and depool it from API or vslow/dump groups if it is present).
```
sudo dbctl instance es1038 set-weight 0
sudo dbctl config commit -m "Set es1038 with weight 0 T368401"
```
[x] Topology changes, move all replicas under NEW primary
```
sudo db-switchover --timeout=25 --only-slave-move es1037 es1038
```
[x] Disable puppet on both nodes
```
sudo cumin 'es1037* or es1038*' 'disable-puppet "primary switchover T368401"'
```
[x] Merge gerrit puppet change to promote NEW primary: https://gerrit.wikimedia.org/r/1049550
**Failover:**
[x] Log the failover:
```
!log Starting es6 eqiad failover from es1037 to es1038 - T368401
```
[x] Switch primaries:
```
sudo db-switchover --skip-slave-move es1037 es1038
echo "===== es1037 (OLD)"; sudo db-mysql es1037 -e 'show slave status\G'
echo "===== es1038 (NEW)"; sudo db-mysql es1038 -e 'show slave status\G'
```
[x] Promote NEW primary in dbctl, and remove read-only
```
sudo dbctl --scope eqiad section es6 set-master es1038
sudo dbctl config commit -m "Promote es1038 to es6 primary T368401"
```
[x] Restart puppet on both hosts:
```
sudo cumin 'es1037* or es1038*' 'run-puppet-agent -e "primary switchover T368401"'
```
**Clean up tasks:**
[] Clean up heartbeat table(s).
```
sudo db-mysql es1038 heartbeat -e "delete from heartbeat where file like 'es1037%';"
```
[] 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 es1038
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 es1037
```
[] Update DNS: https://gerrit.wikimedia.org/r/1049551
[] Update candidate primary dbctl and orchestrator notes
```
sudo dbctl instance es1037 set-candidate-master --section es6 true
sudo dbctl instance es1038 set-candidate-master --section es6 false
(dborch1001): sudo orchestrator-client -c untag -i es1038 --tag name=candidate
(dborch1001): sudo orchestrator-client -c tag -i es1037 --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 = 'es6';"
```
[] (If needed): Depool es1037 for maintenance.
```
sudo dbctl instance es1037 depool
sudo dbctl config commit -m "Depool es1037 T368401"
```
[] Change es1037 weight to mimic the previous weight es1038:
```
sudo dbctl instance es1037 edit
```
[] Enable writes in es6 by merging and deploying revert of mediawiki config patch:
(in deployment.eqiad.org)
```
scap backport 922377
```
FIXME: That number should be the id of gerrit patch of the revert.
[] Update/resolve this ticket.