Instant Overflow Injection - Shifting traffic to overflow providers in a moment's notice (denog16)

Single peering interfaces can get loaded during peak usage and/or failure scenarios while the network as a whole still has spare capacity. As remedy we can use upstream via our so-called overflow providers. In normal operation mode we will prefer direct peerings and only use overflow providers as fallback. For events like the European Football Championship we want to be able to shift traffic to those fallback routes with low effort, low wait times, high granularity and high confidence. We have implemented a service that injects on-demand copies of the existing fallback routes with the preferences tuned to let them be preferred over the "normal" peering routes. The routes are advertised via BGP sessions to our routers and are not distributed any further. The service is using GoBGP and running in Kubernetes. Licensed to the public under http://creativecommons.org/licenses/by/4.0 about this event: https://pretalx.com/denog16/talk/NCYK9Q/