Steps to upgrade:
[x] Sanitarium hosts on both DCs (already done https://phabricator.wikimedia.org/T275112 https://phabricator.wikimedia.org/T272008)
[x] Sanitarium masters on both DCs (https://phabricator.wikimedia.org/T280492)
[x] Available backup source on the standby DC db1171
[x] Candidate master on the standby DC: db1181
[x] Master on the standby DC: db1136
[x] Switchover backup generation standby DC https://gerrit.wikimedia.org/r/c/operations/puppet/+/710977
[x] Candidate master on the primary DC
[x] Available backup source on the primary DC db2098
[] Switchover on the primary DC to promote a Buster+10.4 host to master: T289129
[] Switchover backup generation Primary DC https://gerrit.wikimedia.org/r/c/operations/puppet/+/710981
[] Upgrade the old master and make it a candidate master.
[] Cleanup (remove) old backup sources from both DCs
Please read the [[ https://docs.google.com/document/d/1tYfOYROB_XjD0x_vrCRn8KpjCPUflCDuhKz8cXJvtFk/edit?ts=607fb79e | doc ]] about procedure for more details.
Original master: db2118
Original candidate master: db2121