The native HA feature allows two Cisco DCNM appliances to run as active and standby applications, with their embedded databases synchronized in real time. Therefore, when the active DCNM is not functioning, the standby DCNM will take over with the same database data and resume the operation.
Limitations of native HA:
The native HA is only supported on DCNM appliances with ISO or OVA installation.
Once you enable native HA you could not revert back. The only option to have stand-alone server again is to restart DCNM
When you setup native HA, you need to license only one DCNM server (the one which has been deployed as Active). During failover, Standby server will get the licensing information from the original Active and will work as a licensed server.
Please pay attention, the following values in the ha-setup.properties file should be changed: NODE_ID, PERR_ETH0_IP, VIP_ADDRESS, VIP_PREFIXand VIP_FQDN. If you use Enhanced Fabric Management network, then you also should specify values for VIP1_ADDRESSand VIP1_PREFIX
Split brain and HA-PING
Split-Brain syndrome occurs when the communication on enhanced fabric interface between two HA peers is lost. As the result, both hosts will act as Active. When the communication resumes, both hosts shall negotiate and eventually one will become active, the other standby
In order to avoid the split-brain situations, you could configure optional parameter HA_PING in ha-setup.properties . The address which you configure as HA_Ping should be a 3-rd machine address, i.e. it should not belong one of the DCNM HA instances. The HA_PING address should be reachable from both DCNM servers. It is recommended to use a default-gateway as HA-Ping address.
Question: How I could change the configured network mask (VIP_PREFIX) after ha has been setup?
Answer: please edit /etc/ha.d/haresources and changes virtual network mask there. The file would look like this one:
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