When a browser loads a Notify page it does the following:
- DNS and TLS handshake for notifications.service.gov.uk
- download some HTML
- sees that the HTML needs to load some CSS
- DNS and TLS handshake for static.notifications.service.gov.uk
- downloads the CSS
We can speed things up a bit in modern browsers by parallelizing this
process a bit. Modern browsers support some HTTP headers[1] that allow
them to connect to other origins sooner.
After this change the steps are:
- DNS and TLS handshake for notifications.service.gov.uk
- receive response headers and simultaneously:
- download some HTML
- DNS and TLS handshake for static.notifications.service.gov.uk
- sees that the HTML needs to load some CSS
- downloads the CSS
1. https://developer.mozilla.org/en-US/docs/Web/Performance/dns-prefetch