What is the maximum allowed round trip time (RTT) between 2 nodes?

Consul reference architecture mentions below statement -

“In any case, there should be high-bandwidth, low-latency (sub 8ms round trip) connectivity between the failure domains.”

What happens if the RTT is more than 8ms? What is the maximum allowed RTT between 2 nodes in a cluster?

This latency requirement primarily applies to Raft protocol communication between servers within a Consul datacenter. Higher latency values could affect the availability of cluster. See the server performance page in the Consul docs for variables that can be tuned to potentially allow for more latency between server agents.

Consul clients can likely operate at higher thresholds than servers. We are in the process of determining a reasonable latency ceiling. We will update our documentation with this information once that range has been determined.