plugins/grpc: default value for grpc port

[jackstar12]

The gRPC server will always start this way. Current port choice is arbitrary, open to suggestions.

closes: #7473

[niftynei]

ACK 9127f94

[cdecker]

The change in the behavior appears to cause the cln-grpc-plugin to terminate almost immediately which is causing the tests to also fail right away. Can you check what is causing the plugin to exit?

[jackstar12]

Can you check what is causing the plugin to exit?

The test is starting two nodes and both are now trying to use the default port 9736 for the cln-grpc plugin which is causing one of them to crash

[rustyrussell]

So, when people upgrade they will have a new random port open to the internet?

I know @michael1011 wants this, but would it be sufficient to open a localhost-bound port by default in this case?

[michael1011]

So, when people upgrade they will have a new random port open to the internet?

I know @michael1011 wants this, but would it be sufficient to open a localhost-bound port by default in this case?

@rustyrussell that's a very valid point. What about adding an option to configure the host on which the plugin will listen and defaulting that to 127.0.0.1?

Edit: I can't think of any other sensible option, so let's do that. The only concern is that it's a breaking change for all existing CLNs that have a gRPC port configured and expect the plugin to listen on 0.0.0.0.

[ShahanaFarooqui]

@jackstar12 Thanks for the PR. Just FYI, I reordered the commits to move 'set default grpc-host to localhost' before the tests. This ensures that test_clnrest with l1.daemon.wait_for_logs([r'serving grpc on 127.0.0.1:' does not fail.

ACK 467fbaa.

[rustyrussell]

Only problem now is that this will break existing setups which set grpc-port and do an upgrade!

Suggest that the default grpc-host be localhost IF the port is not specified, otherwise 0.0.0.0?

[ShahanaFarooqui]

Only problem now is that this will break existing setups which set grpc-port and do an upgrade!

Suggest that the default grpc-host be localhost IF the port is not specified, otherwise 0.0.0.0?

Shouldn't we instead encourage existing users to explicitly configure their grpc-host to limit their node's exposure? New users who wish to run cln-grpc on a custom port may unintentionally expose their node on 0.0.0.0 if they assume the default grpc-host setting of localhost applies universally. We can update the docs to make this clearer, but it might be a good idea to ask existing users to set their grpc-host intentionally and understand the risks.

[jackstar12]

While the suggestion from @rustyrussell would maintain backward compatibility, it could become burdensome in the future and complicated to explain in the documentation. So, I think it's easier to simply mention the change in the release notes and have all gRPC users verify whether it affects their setup.