How SNI actually works: the TLS feature powering CDNs and multi-tenant routing
HankYeomans · x · 2026-09-29
Gwen Shapira explains SNI (Server Name Indication), an underappreciated feature of modern network protocols: a server may have multiple DNS names, and it must present the right certificate to every client regardless of which name was used.
The client includes the hostname in its opening TLS message, letting the server select the correct certificate—and also run 'business logic' based on the hostname, such as routing and tenant isolation.
That's how CDNs route to the correct app, and most multi-tenant services rely on SNI to work.
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