Problem Description
After upgrading to Aerospike 8.1.0.x you see the following error when using the asadm command 'show user-agents'
Admin> show user-agents
ERROR: Error processing user agent data from 1.2.3.4:3000: 'user-agent'
Explanation
This command is new to the 8.1.0.x product release, so if the cluster is left in a mixed state during or after upgrade, it's possible for a node on an older version to report missing or no data and cause the failure.
Solution
Ensure all nodes in the cluster are fully upgraded to the release that supports the user-agent command.
If all nodes are already upgraded, restart the nodes in the cluster to ensure all connection tables and info protocol entries are refreshed.
Notes
https://aerospike.com/docs/database/release/8-1