Maximum RTT within a datacenter

[Miguel Terron]

Reading Consul documentation, the definition of a datacenter is very loosely defined as "a networking environment that is private, low latency, and high bandwidth".
In this context, what does "low latency" means? In my case, I have two datacenters with a RTT of 12ms, is that latency low enough? I understand the effect of latency on data replication but would like some guidance on the limits of Consul deployments in physically remote deployments.

Thanks

[Armon Dadgar]

Miguel,

That is probably right at the limit of what we'd consider a LAN. There is no hard and fast rule, however the concerns are with the tuning of the gossip layer which expects a certain timeliness of responses and the Raft consensus layer which also requires fairly tight latency promises.

Both layers can handle spikes up to hundreds of milliseconds, but they typical will experience higher levels of errors as latency increases. For this reason we typically recommend a maximum network latency of 10ms for LAN, but you may get away with 12.

Best bet is to just try it and see how things go. I'd be happy to suggest possible tunes to both of those layers, although you'd need to recompile to overwrite our defaults.

Hope that helps!

Best Regards,

Armon Dadgar

Sent from my iPhone

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[Miguel Terron]

Thanks for the answer Armon. It'd be good to have some of this numbers on the official documentation.