An nginx location selects configuration for a request within the chosen server. For the flat prefix and regex locations tested here, an exact match finishes the search; otherwise nginx remembers the longest matching prefix and can then choose the first matching regex. If no applicable regex wins, the remembered prefix supplies the configuration. This is a selection process, not simply the first block encountered in the file. ...
Anycast gives an address several homes. Multiple sites announce the same prefix, and each network selects one usable path according to its BGP policy. A client usually lands at a topologically close replica without first contacting a global load balancer. When one site withdraws its announcement, the control plane can converge on another home. ...
Aggregation replaces a set of adjacent prefixes with one covering announcement, so every peer downstream stores one entry instead of dozens and stops processing updates for each component. The table gets smaller, and the churn of a flapping edge stops propagating outward. ...
An IPv4 default route is the prefix 0.0.0.0/0: it matches every IPv4 destination, with the least possible specificity. In a selected routing table, a longer matching prefix normally takes precedence. The default is not a procedure that retries whenever a more specific route fails. Routing policy selects relevant tables, and the chosen route describes a forwarding decision rather than promising that the entire round trip will succeed. ...
BGP is the only protocol that stitches tens of thousands of independently operated networks into one forwarding table. It carries reachability, but what it really carries is policy: each network says which prefixes it originates, which neighbours it learned them from, and — through filters — which ones it is willing to pass on. ...
nginx proxy_pass chooses an upstream destination and also affects the request URI sent there. The important distinction is whether the directive includes a URI component, not simply whether its text ends with a slash. In an ordinary prefix location, a literal target URI replaces the matching normalized prefix. An authority-only target can pass the original request URI when the request has not been rewritten. ...