How do I add a resolve.alias fallback in case the CDN is down?

[marIbarra8]

Hello. I am bundling my app using Vite. I am using React and ReactDOM and I noticed that they made my bundle huge so I am importing them externally from a CDN instead of including it in the bundle. This a relevant snippet of my vite.config.js:

export default defineConfig({
  resolve: {
    alias: {
      'react': 'https://esm.sh/react@18.2.0',
      'react-dom': 'https://esm.sh/react-dom@18.2.0'
    }
  };

I know that if the CDN I'm using (esm.sh) is down, my whole app will be down as well because it is dependent on react and react dom. Is there anything I can do to add an alternative CDN in case this happens? Or are there any other solutions?

[vekovius]

resolve.alias is the wrong layer for runtime CDN failover.

What you have now is really just telling Vite/Rollup to rewrite the import source during bundling/dev resolution. It does not give you a real “try CDN A, then CDN B” runtime fallback.
If you care about availability, I’d strongly recommend one of these instead:

1. Bundle React normally

   • This is the simplest and most reliable option.
   • For most apps, externalizing React to a CDN is not worth the operational fragility unless you have a very specific constraint.

2. Use explicit runtime loading in HTML

   • e.g. import maps or script tags that you control from the server/CDN edge
   • then you can implement a real fallback strategy there
   • this is more of an app delivery concern than a Vite config concern

3. Use a primary CDN with a server-controlled fallback

   • for example: your own origin or edge cache serves as the stable URL
   • that origin can pull from upstream and gives you a single dependable URL in the app

If you keep React external, I would not try to solve HA through Vite aliasing. I’d solve it at the deployment/runtime layer.

So the short answer is: no, resolve.alias is not the right mechanism for CDN failover. The better answer is either bundle React, or move the fallback logic to HTML/runtime/infrastructure.