Downscaling the cluster¶
Downscaling can have an adverse effect on the availability and resiliency of the cluster, especially when a member is being removed that runs an OVN central service (OVN SB, OVN NB, OVN Northd).
OVN uses the Raft consensus algorithm for cluster management, which has a
fault tolerance of up to
(N-1)/2 members. This means that fault resiliency
will be lost if a three-node cluster is reduced to two nodes.
You can watch logs on the departing member for indications of removal failures with:
snap logs -f microovn.daemon
Any issues that arise during the removal process will need to be resolved manually.
Remove a cluster member¶
To remove a cluster member:
microovn cluster remove <member_name>
The value of
<member_name> is taken from the Name column in the output
of the cluster list command.
Any chassis components (
ovs-vswitchd) running on the
member will first be stopped and disabled (prevented from starting). For a
member with central components present (
microovn.central), the Northbound
and Southbound databases will be gracefully removed.
Upon removal, check the state of OVN services to ensure that the member was properly removed.
# Check status of OVN SB cluster
microovn.ovn-appctl -t /var/snap/microovn/common/run/central/ovnsb_db.ctl cluster/status OVN_Southbound
# Check status of OVN NB cluster
microovn.ovn-appctl -t /var/snap/microovn/common/run/central/ovnnb_db.ctl cluster/status OVN_Northbound
# Check registered chassis
MicroOVN will back up selected data directories into the timestamped location
/var/snap/microovn/common/backup_<timestamp>/. These backups will
OVN database files
OVS database file
issued certificates and keys