"As these requirements were hitting us, there was no open source out there able to meet them," he says. "And once you start on a path where you're starting to build out infrastructure and system, even if there's something else that comes along and addresses those requirements the switching cost is pretty huge. It's not an aversion to it; it's that we haven't seen open source out there that really meets our needs, and there's a switching cost that we have to take into account, which will slow us down."
Microsoft is, however, considering contributing the Azure Service Fabric architecture to the open source community, Russinovich said. But there has to be some symbiosis.
"What's secret sauce, what's not; what's the cost of contributing to open source, what's the benefit to customers of open source, what's the benefit to us penetrating markets," he says. "It's a constant evaluation."
Some of the challenges in constructing the Azure SDN were retrofitting existing controllers into the Service Fabric, Russinovich says. That resulted in some scaling issues.
"Some of the original controllers were written not using Service Fabric so they were not microservice oriented," he says. "We immediately started to run into scale challenges with that. Existing ones are being (rewritten) onto Service Fabric.
"Another one is this evolution of the VFP and how it does packet processing. That is not something that we sat down initially and said, it's connections, not flows.' We need to make sure that packet processing on every packet after the connection is set up needs to be highly efficient. It's been the challenge of being able to operate efficiently, scale it up quickly, being able to deliver features into it quickly, and being able to take the load off the server so we can run VMs on it."
What's next for the Azure SDN? Preparing for more explosive growth of the Microsoft cloud, Russinovich says.
"It's a constant evolution in terms of functionality and features," he says. "You're going to see us get more richer and powerful abstractions at the network level from a customer API perspective. We're going to see 10X scale in a few years."
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