I have two indexers A and B.
UF always send data to A. If A is down, then UF send data to B. Is it possible to enforce so?
This is not possible to achieve within Splulnk, using outputs.conf. You would need to use external DNS load balancer with HA design.
Yes, you can configure autoLB in output.conf. Example:
server = splunk1:9997,splunk2:9997,splunk3:9997
autoLB = true
forceTimebasedAutoLB = true
autoLBFrequency = 40
For details, please refer to this topic:
Hope it helps. Thank!