Canaries in the Network
Updating a large network deployment is a dangerous process. Regardless of whether the operation is a switch BGP configuration change or a network wide SDN controller upgrade, misconfigurations and bugs can potentially cause network outages and downtime for critical cloud services. Many cloud applications have adopted a useful strategy that networks have tried to emulate: phased rollouts, in which a small fraction of users are redirected to the updated version while most users continue unassailed. Unfortunately, this analogy is fundamentally flawed. This paper explores the limits of phased rollouts in networks and shows when and why they can fail. We also go on to propose two preliminary designs for approximating the benefits of phased rollouts. Although preliminary, we argue that our designs can achieve a useful level of isolation between a 'known correct' and 'new' control plane.
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