* mini: reserve the admin gRPC port instead of binding it late
Port selection probes every port with a throwaway listener and closes it.
Master, filer, volume and S3 bind a moment later, but the admin waits for
all of them first and only then binds its worker gRPC port, roughly two
seconds in. That port defaults to the admin http port + 10000, which lands
inside the Linux ephemeral range, so one of the cluster's own outgoing gRPC
dials can take it during the gap and the admin dies on bind, taking the
worker with it.
Keep the listener from the availability check and hand it to the admin.
* mini: clear the admin gRPC reservation before retaking it
A rerun inside one process would otherwise inherit the closed listener of
the previous run whenever the reservation fails, and the admin would accept
it and only find out inside Serve.
* mini: snapshot the admin options for the startup goroutine
The cleanup path read the package-level options long after the goroutine
started, so a later in-process run could have its reserved listener closed
by the previous run.
Chris LuandGitHub
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