The summary.
EACH HTTP VERSION ADDRESSED THE BOTTLENECK THE LAST ONE EXPOSED
Version two removed application-layer blocking but left transport-layer blocking. Version three, over QUIC, removes that.
The benefit is largest on high-latency, lossy connections — which is exactly this market.
MULTIPLEXING MADE OLD OPTIMISATIONS COUNTERPRODUCTIVE
Splitting assets across hostnames and bundling purely to reduce requests now hurt, because separate files cache independently.
VERIFY WHICH PROTOCOL IS ACTUALLY NEGOTIATED
In a layered setup, the component terminating the client connection decides — not the origin behind it.
TLS PROVES IDENTITY, NOT HONESTY
Disable everything before the current two versions, enable forward secrecy, and test with an external assessment tool.
SERVE THE FULL CHAIN
Omitting intermediates makes some clients fail and others succeed, which is the hardest kind of fault to diagnose.
MONITOR CERTIFICATE EXPIRY FROM OUTSIDE
Checking your own automation only confirms it believes it succeeded. Silent renewal failure is the commonest cause of a complete outage.
