cmd, node: initialize ports with --instance

[weiihann]

Description

This PR adds a new CLI flag called --instance <value>, used to configure ports when running multiple nodes on the same machine to avoid port conflicts. This is only applicable for port, authrpc.port, discovery,port, http.port, ws.port.

The calculation of port numbers is as follows:

authrpc.port = 8551 (default) + `instance`*100 - 100
http.port = 8545 (default) - `instance` + 1
ws.port = 8546 (default) + `instance`*2 - 2
port = 30303 (default) + `instance` - 1
discovery.port = 30303 (default) + `instance` - 1

In a scenario where the user specify both --instance and the supported port list (i.e. port, authrpc.port, ...), then the ports specified will supersede the port values configured by --instance.

Example

Usage: geth --instance 2

authrpc.port = 8651
http.port = 8544
ws.port = 8548
port = 30304
discovery.port = 30304

Usage: geth --instance 2 --authrpc.port 8551

authrpc.port = 8551
http.port = 8544
ws.port = 8548
port = 30304
discovery.port = 30304

Usage: geth --instance 201

Fatal: Instance number 201 is too high, maximum is 200

Credits

This flag is inspired by reth.

[jwasinger]

I can see how this flag would be useful when running multiple local nodes on the same host. Because the main use-case for this is for testing, I would opt to not include this flag in Geth.

[jwasinger]

This should be a complete explanation of what this flag does, similarly to the full description from reth:

          Add a new instance of a node.
          
          Configures the ports of the node to avoid conflicts with the defaults. This is useful for running multiple nodes on the same machine.
          
          Max number of instances is 200. It is chosen in a way so that it's not possible to have port numbers that conflict with each other.
          
          Changes to the following port numbers: - DISCOVERY_PORT: default + `instance` - 1 - AUTH_PORT: default + `instance` * 100 - 100 - HTTP_RPC_PORT: default - `instance` + 1 - WS_RPC_PORT: default + `instance` * 2 - 2

[weiihann]

Amended.

[weiihann]

I can see how this flag would be useful when running multiple local nodes on the same host. Because the main use-case for this is for testing, I would opt to not include this flag in Geth.

Primarily, I think users would need to run multiple nodes in this scenario:

1. Running different nodes on mainnet and testnets
2. Running different L1 nodes
3. Running L1 and L2 nodes (perhaps fork of geth)
4. Testing

For me, I encountered the need to run multiple nodes when I was running 1 mainnet node and 2 testnet nodes. So having this flag would save me some time figuring out the correct ports. For users that are not that familiar with ports, this will save them some trouble.