To resolve this warning, I added a Cache-Control header with the value max-age=31536000 to the HTTP responses of my domain (31536000 is the number of seconds in a year).

I host nelson.cloud on Amazon CloudFront. I added this header to the CloudFront Distribution that the nelson.cloud domain points to. This can be done by adding a “Response headers policy” in the Behavior of the Distribution. I wrote a post demonstrating how to do this in detail: How to Add a Custom Response Header to an Amazon CloudFront Distribution.

After the header was configured, I checked PageSpeed Insights again and the warning had gone away for the assets under my domain nelson.cloud:

(The remaining asset is not under my control so I can’t fix that one.)

Note:

You may be able to use a different value smaller than 31536000 for your header. I chose a year in seconds to be on the safe side for PageSpeed Insights.

References

• https://developer.chrome.com/docs/lighthouse/performance/uses-long-cache-ttl/
• https://developer.mozilla.org/en-US/docs/Web/HTTP/Reference/Headers/Cache-Control
• https://docs.aws.amazon.com/AmazonCloudFront/latest/DeveloperGuide/Expiration.html