Proxies, Load Balancers & CDNs
Forward vs reverse proxies, L4 vs L7 balancing, health checks, and the networking view of a CDN: DNS, edge locations, caches and geographic distance.
A proxy is a process that terminates one connection and opens another; whether it acts for the client (forward) or for the server fleet (reverse) decides who knows about it, what it may rewrite, and which headers you can trust.
A load balancer either forwards TCP connections it never reads (L4: cheap, protocol-blind) or terminates HTTP and routes requests it understands (L7: smarter, costlier) — and in both cases its health checks, draining and idle timeouts decide what 502 and 504 mean.
A CDN moves the TCP/TLS endpoint and a cache to within a few milliseconds of the client, because the one cost no engineering removes is the speed of light in fibre; what it cannot cache still pays the trip to the origin.