* First level of loadbalancing is DNS[2]. here we try to map user to a closest PoP based on metrics from our clients.
* User to a PoP path after that mostly depends on our BGP peering with other ISPs (we have an open peering policy[3], please peer with us!)
* Within the PoP we use BGP ECMP and a set of L4 loadbalancers (previously IPVS, now Katran[4]) that encapsulate traffic and DSR it to L7 balancers (previously nginx, now mostly Envoy.)
Overall, we have ~25 PoPs and 4 datacenters.
[1] https://dropbox.tech/infrastructure/dropbox-traffic-infrastr... [2] https://dropbox.tech/infrastructure/intelligent-dns-based-lo...
[3] https://www.dropbox.com/peering [4] https://github.com/facebookincubator/katran
He also contributed a lot to Envoy migration migrating our desktop client to it and adding perf-related thing like TLS session tickets' lifetime to SDS.
"we have an open peering policy"
That's a bit of a lie given you have a minimum 50Mbps requirement before you even consider a peering request.
I would call that Selective, not Open !
What I wonder about is how do you distribute the traffic on the higher level? I imagine there are separate clusters of envoys to serve different configurations/applications/locations? How many datacenters does dropbox have?
I was running a comparable setup in a large company, all based on HAProxy, there was a significant amount of complexity in routing requests to applications that might ultimately be in any of 30 datacenters.