When I was at google, the big outages were almost always bad routing to the service - it was never that the service couldn't handle the load, and bad service in

When I was at google, the big outages were almost always bad routing to the service - it was never that the service couldn't handle the load, and bad service instances were kind of hidden. my service did have some problems on new releases, but because we had multiple instances we could just redirect traffic to the instances we hadn't updated, so they stayed up.