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Azure/azure-functions-host
The host/runtime that powers Azure Functions
This is the actual runtime that executes Azure Functions — the host process that loads your function app, manages worker processes via gRPC, dispatches triggers, and handles the function lifecycle. If you've ever wondered what happens between your function code and Azure infrastructure, it's here. Useful reading for anyone doing deep Azure Functions debugging or building custom extensions.
The gRPC worker channel architecture (src/WebJobs.Script.Grpc/) is well-structured — the separation between OrderedInvocationMessageDispatcher and the channel itself makes the invocation pipeline legible. The isolated worker model is properly first-class now, not bolted on. CI pipeline is thorough: separate cold-start benchmarking, integration tests, and perf benchmarks as distinct pipeline definitions rather than one monolithic YAML. The JSON schema files for function.json and extensions.json are useful for anyone building tooling.
The sample code in /sample/CSharp/ still uses the old .csx scripting model with function.json sidecars — that model is dead for new development but the samples haven't been updated, which will confuse newcomers. The README is basically empty for a project of this complexity: no architecture overview, no contributor setup guide, no pointer to where the interesting code actually lives. Having both 'in-proc' and 'dev' branches in active CI is a maintenance burden that reflects the painful in-process model deprecation — in-proc isn't going away as fast as Microsoft would like. The gRPC proto definitions are pulled from a separate repo, so you can't do a fully self-contained build without tracking down the right version of azure-functions-language-worker-protobuf.