**Checklist:**
NEW primary: db2107
OLD primary: db2104
[x] Check configuration differences between new and old primary:
```
sudo pt-config-diff --defaults-file /root/.my.cnf h=db2104.codfw.wmnet h=db2107.codfw.wmnet
```
**Failover prep:**
[] Silence alerts on all hosts:
```
sudo cookbook sre.hosts.downtime --hours 1 -r "Primary switchover s2 T317627" 'A:db-section-s2'
```
[] Set NEW primary with weight 0 (and depool it from API or vslow/dump groups if it is present).
```
sudo dbctl instance db2107 set-weight 0
sudo dbctl config commit -m "Set db2107 with weight 0 T317627"
```
[] Topology changes, move all replicas under NEW primary
```
sudo db-switchover --timeout=25 --only-slave-move db2104 db2107
```
[] Disable puppet on both nodes
```
sudo cumin 'db2104* or db2107*' 'disable-puppet "primary switchover T317627"'
```
[] Merge gerrit puppet change to promote NEW primary: FIXME
**Failover:**
[] Log the failover:
```
!log Starting s2 codfw failover from db2104 to db2107 - T317627
```
[] Set section read-only:
```
sudo dbctl --scope codfw section s2 ro "Maintenance until 06:15 UTC - T317627"
sudo dbctl config commit -m "Set s2 codfw as read-only for maintenance - T317627"
```
[] Check s2 is indeed read-only
[] Switch primaries:
```
sudo db-switchover --skip-slave-move db2104 db2107
echo "===== db2104 (OLD)"; sudo db-mysql db2104 -e 'show slave status\G'
echo "===== db2107 (NEW)"; sudo db-mysql db2107 -e 'show slave status\G'
```
[] Promote NEW primary in dbctl, and remove read-only
```
sudo dbctl --scope codfw section s2 set-master db2107
sudo dbctl --scope codfw section s2 rw
sudo dbctl config commit -m "Promote db2107 to s2 primary and set section read-write T317627"
```
[] Restart puppet on both hosts:
```
sudo cumin 'db2104* or db2107*' 'run-puppet-agent -e "primary switchover T317627"'
```
**Clean up tasks:**
[] Clean up heartbeat table(s).
```
sudo db-mysql db2107 heartbeat -e "delete from heartbeat where file like 'db2104%';"
```
[] change events for query killer:
```
events_coredb_master.sql on the new primary db2107
events_coredb_slave.sql on the new slave db2104
```
[] Update DNS: FIXME
[] Update candidate primary dbctl and orchestrator notes
```
sudo dbctl instance db2104 set-candidate-master --section s2 true
sudo dbctl instance db2107 set-candidate-master --section s2 false
(dborch1001): sudo orchestrator-client -c untag -i db2107 --tag name=candidate
(dborch1001): sudo orchestrator-client -c tag -i db2104 --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 db1115 zarcillo -e "select * from masters where section = 's2';"
```
[] (If needed): Depool db2104 for maintenance.
```
sudo dbctl instance db2104 depool
sudo dbctl config commit -m "Depool db2104 T317627"
```
[] Change db2104 weight to mimic the previous weight db2107:
```
sudo dbctl instance db2104 edit
```
[] Apply outstanding schema changes to db2104 (if any)
[] Update/resolve this ticket.