[FrontEnd] Keep RPC server tcp protocol

[esmeetu]

Motivation: Keep RPC tcp mode is useful when we want to deploy api server and vllm engine server on different machine.

Related PR: #7222

Furthermore, i want to decouple api server with vllm engine server in the future, where we can update one of them without shutdown another server.

Use case:

# start rpc server on Node1
vllm serve model_arg --engine-use-rpc

# start api server on Node2
vllm start --adress tcp://Node1:5570

vLLM RPC System(Experimental):

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[youkaichao]

where we can update one of them without shutdown another server

looks like a corner case. what's the motivation for this? when you shutdown the engine server, the api server is not usable.

[robertgshaw2-neuralmagic]

As part of this, we need to make sure that port selection is robust

[njhill]

I think the main thing is that we make it clear the interface/protocol between the two procs is not yet stable, will likely change over the next few versions as we refine things.

[esmeetu]

where we can update one of them without shutdown another server

looks like a corner case. what's the motivation for this? when you shutdown the engine server, the api server is not usable.

Yes, but when i reboot api server(light), i won't touch engine server (heavy, might multi-node serving the large model). But ipc mode can also achieve this if we know the ipc path. And rpc mode just for distributed server environment.

[esmeetu]

I think the main thing is that we make it clear the interface/protocol between the two procs is not yet stable, will likely change over the next few versions as we refine things.

Yes, and I also add some ideas in the description.

[esmeetu]

As part of this, we need to make sure that port selection is robust

ok, will look into this. But currently we can use VLLM_RPC_PORT to control.

[youkaichao]

when i reboot api server(light), i won't touch engine server (heavy, might multi-node serving the large model)

can you elaborate on this? what's the usecase of rebooting just the api server?

[esmeetu]

when i reboot api server(light), i won't touch engine server (heavy, might multi-node serving the large model)

can you elaborate on this? what's the usecase of rebooting just the api server?

Such as adding some features for api server or api server crash for some reason.