Walk me through everything that happens when a client sends an HTTPS request to your service.

The client resolves the hostname through DNS, opens a TCP connection to the resolved address or reuses an existing one, then completes a TLS handshake that validates the server certificate and agrees session keys. The encrypted request travels through load balancers and proxies to your application, which handles it and writes a response back over the same connection. Keep alive and HTTP/2 multiplexing let later requests skip most of the setup.

First the client needs an address, so it checks its own cache, then the OS resolver, then a recursive resolver, and gets back an IP with a time to live. Then a TCP handshake to that address, unless there is already an open connection in the pool, which there usually is. Then TLS: the server presents a certificate chain, the client validates it against its trust store and checks the hostname matches, and they agree session keys. With TLS 1.3 that is one round trip, or zero on a resumed session. The request goes out encrypted, and in practice it hits a CDN or load balancer first, which usually terminates TLS and opens its own connection to my service. My app handles it and the response comes back the same way. The reason I care about the sequence is latency: on mobile the first request pays DNS plus TCP plus TLS before a byte of my code runs, so connection reuse is often the biggest win available.