nimbus-eth1/lc_proxy/docs/metamask_configuration.md

MetaMask configuration with Alchemy provider

This documents shows how to build and start light client proxy on Goerli network and pair it with the MetaMask browser extension.

1. Build light client proxy

First build light client proxy as explained here.

2. Configuring and running light client proxy

To run the binary built in previous step with Goerli config and using Alchemy data provider, run:

# From the nimbus-eth1 repository
./build/lc_proxy --trusted-block-root:TrustedBlockRoot --web3-url="wss://eth-goerli.g.alchemy.com/v2/ApiKey" --network=goerli

ApiKey: personal API key assigned by Alchemy

TrustedBlockRoot: Trusted block root, from which the consensus light client will start synchronization

This command also starts an HTTP server with address http://127.0.0.1:8545 to listen for incoming JSON RPC requests.

After startup, light client will start looking for suitable peers in the network, i.e peers which serve light client data, and will then start syncing. During syncing most of the RPC endpoints will be inactive and will fail to respond to queries. This happens because the light client proxy can't verify responses from the data provider until the consensus light client is in sync with the consensus chain.

When the light client is in sync, the following line should be visible in the logs:

NOT 2022-09-29 10:06:15.974+02:00 New LC optimistic block                    opt=81de61ec:3994230 wallSlot=3994231

After receiving the first optimistic block, the proxy is ready to be used with MetaMask.

3. Configuring MetaMask extension to use custom network

To add custom network in MetaMask browser extension:

1. Go to settings
2. In settings, go to networks tab
3. Click on the Add a network button.
4. The most important fields when adding a new network are New RPC URL and Chain ID. New RPC URL should be configured to point to the HTTP server started with proxy. In this example it will be http://127.0.0.1:8545. Chain ID should be set to the chain id of the network used by proxy. The chain id for Goerli is 5.

If everyting went smooth there should be new network in Networks drop down menu.

After switching to this network it should be possible to create new accounts, and perform transfers between them.

NOTE: Currently when adding a custom network with a chain id which already exists in the MetaMask configuration, MetaMask will highlight this as an error. This should be ignored as this is really a warning, and it is a known bug in MetaMask.