How to set multiple nodes in HttpProvider web3 v1.2.0

Question

I'm working with Nodejs application, and using a multi-node setup on different servers.

If I have single node end point like http://localhost:8545 I can use Web3 providers as below

var web3 = new Web3(new Web3.providers.HttpProvider('http://localhost:8545'));

However, I'm not sure how to setup multiple nodes into it. So the first node becomes unhealthy, the system uses the second node and so on.

I have tried with multi-http-provider but it seems not working with web3 v1.2.0

but it seems not working: having an error of uncaughtException : RangeError: Maximum call stack size exceeded

Answer 1

The following script might help you to achieve the multi-providers case (it is written in Node.js using TypeScript and is quite lightweight):

import Web3 from 'web3';
require('dotenv').config();
const infuraKey = process.env.INFURA_KEY;

// We assign a default web3 provider
let web3 = new Web3(new Web3.providers.HttpProvider('http://127.0.0.1:7545'));

// List of our web3 providers
const providers = [
   new Web3(new Web3.providers.HttpProvider('http://127.0.0.1:7545')),
   new Web3(new 
Web3.providers.HttpProvider(`https://ropsten.infura.io/v3/${infuraKey}`)),
];

// Selects the first web3 provider available from our list
const providerSelector = async () => {
   let selectedProvider = null;
   for (let i = 0; i < providers.length; i++) {
       await providers[i].eth.getBlockNumber()
           .then(() => { selectedProvider = providers[i] })
           .catch(() => { console.log(`Provider ${i} not available`) });
       if (selectedProvider) {
           web3 = selectedProvider;
           return true;
       };
   };
   return false;
};

const main = async () => {
   // Example (here we can put any query, transaction, etc)
   web3.eth.getBlockNumber()
      .then(() => { 
         // Do our stuff
      })
      .catch(async (err) => {
         // If current provider is not available, try another one from the list
         const res = JSON.stringify(err, Object.getOwnPropertyNames(err));
         if (res.includes('Invalid JSON RPC response'))
            (await providerSelector()) ? main() : console.log('No providers available');
      });
};

main();

So we have basically providers, which is our list of web3 providers to that we will use depending on their availability.

Whenever we launch a transaction or do any interaction with web3, we need to catch the error exception and in case it is an Invalid JSON RPC response, then we will try finding a new provider and re-try the same function recursively.

In case that no provider is available, the function will just finish because the providerSelector function will return false.