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isle/tasks/misc/open-port-checker.md

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/nats/rpc.md

A mechanism should be developed, using NATS, for a host A to double check that host B can connect to it on a certain host:port. This can be used for a couple use-cases:

  • Make sure that VPN public address is connectable prior to being configured.

  • Make sure that garage RPC port is connectable prior to being configured.

  • Make sure that HTTP(s) ports are connectable prior to being configured (future).

The host which is configuring a port to be opened will always be the one to initiate the process. It will:

  • Open a dummy HTTP server on the port in question, with a handler which always returns a randomly generated token.

  • Publish an RPC request on NATS which indicates which host:port it wishes to confirm connectability and the token.

  • Waits for a response to the NATS request indicating either that the connection was successful, or an error indicating why it wasn't. Errors could include:

    • Timeout (probably blocked by firewall)
    • Challenge token not returned (something else is listening at that port)