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Use Infura as a backup for your node

In this tutorial, you'll use Caddy to set up a reverse proxy with two upstreams, one from your own node, and one from Infura as a backup.

Prerequisites​

Steps​

1. Create a project directory​

Create a new directory for your project. You can do this from the command line:

mkdir reverseProxy

Change into the new directory:

cd reverseProxy

2. Install Caddy​

Install Caddy in the project directory using Homebrew:

brew install caddy

3. Create a Node.js stub​

You may be running your own Ethereum node, but for the sake of this tutorial, you can substitute a node with a Node.js stub. Create a file named main.js in the project directory with the following content:

const https = require("https")
const fs = require("fs")
const options = {
  key: fs.readFileSync("<PATH_TO_CERTIFICATE_KEY_FILE>.pem"),
  cert: fs.readFileSync("<PATH_TO_CERTIFICATE_FILE>.pem"),
}

const hostname = "127.0.0.1"
const port = 9000

const server = https.createServer(options, function (req, res) {
  res.statusCode = 200
  res.setHeader("Content-Type", "text/plain")
  setTimeout(() => {
    res.end("Reverse proxy success!\n")
  }, 1000)
})

server.listen(port, hostname, () => {
  console.log(`Server running at https://${hostname}:${port}/`)
})

This sets up a backend HTTPS service running on 127.0.0.1:9000 (localhost:9000) and displays a success message if the proxy works.

warning

When creating a reverse proxy with multiple upstreams, Caddy requires all upstream endpoints to be HTTP or HTTPS. In this tutorial, because the backup Infura endpoint is HTTPS, you must create a TLS certificate for your localhost (if you're not already using your own private HTTPS node).

You can install and use mkcert to generate a certificate key file and certificate file for your stub:

brew install mkcert
mkcert -install
mkcert localhost

Replace <PATH_TO_CERTIFICATE_KEY_FILE> and <PATH_TO_CERTIFICATE_FILE> in main.js with the generated files.

4. Run the Node.js stub​

In a new terminal window, from your project directory, start the Node.js stub and leave that connection open:

node main.js

5. Create the reverse proxy​

To create the reverse proxy, create a text file named Caddyfile with the following content:

localhost:3000

reverse_proxy https://localhost:9000 https://sepolia.infura.io {
  header_up Host {/v3/<YOUR-API-KEY>}
}

Ensure you replace <YOUR-API-KEY> with the API key for your Ethereum project.

In this example, the reverse proxy retrieves information from localhost:9000, and redirects it to localhost:3000. If localhost:9000 stops responding, Caddy will move on to retrieve information from the Sepolia endpoint. Using header_up Host allows you to include your API key to both the Sepolia and localhost endpoints.

6. Run the reverse proxy​

In a new terminal window, from your project directory, run the reverse proxy using Caddy:

caddy run

7. Make a request​

In a new terminal window, make a curl request to localhost. The following example executes a web3_clientVersion request:

curl http://localhost:3000/v3/<YOUR-API-KEY> \
  -X POST \
  -H "Content-Type: application/json" \
  -d '{"jsonrpc": "2.0", "method": "web3_clientVersion", "params": [], "id": 1}'

The success message from main.js should display, because you've asked the reverse proxy to go to localhost:9000 first.

If you close the Node.js server and send the request again, you should get the result from the Sepolia node:

curl http://localhost:3000/v3/<YOUR-API-KEY> \
  -X POST \
  -H "Content-Type: application/json" \
  -d '{"jsonrpc": "2.0", "method": "web3_clientVersion", "params": [], "id": 1}'

The reverse proxy ignores the localhost node, since it's not functioning, and falls back to the Sepolia node.

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