To Coordinate Or Not To Coordinate? Wide-Area Traffic Management for Data Centers
In this paper, we study the impact of coordinating the selection
of data centers for clients (“mapping”) and performing
multi-homed network-routing (“routing”) from data centers,
two decisions which are conventionally managed independently.
We model their functional separation and degrees of
coordination through an optimization framework, and study
the impact of coordination on (i) service performance, (ii)
robustness to traffic variability, and (iii) bandwidth costs.
We show that in theory, performing mapping and routing independently
can lead to much lower performance or higher
costs than a coordinated decision. In practice, our tracebased
evaluations on an operational CDN show that coarsegrained
information-sharing between mapping and routing is
sufficient for near-optimal request latencies, but not minimal
costs. Further, even complete information-sharing between
mapping and routing is not sufficiently robust to traffic variability,
as ISP-links can easily be overwhelmed due to traffic
burstiness. To address this issue, we design a coordination
technique which is much more robust to traffic variability,
and is also provably optimal.