add: rewriter logic and tests

src/main.rs

@@ -6,9 +6,16 @@ use env_logger::Env;
 use log::info;
 use rewriter::Rewriter;
 
-/// Rewrites nginx configs when new nodes show up in a kubernetes cluster.
+/// Implements a HTTP server which allows clients to 'register'
-/// This package implements the 'proxy end'; another binary is run on the
+/// themselves. Their IP address will be used to replace a
-/// Kubernetes cluster which executes when a node goes down or comes up.
+/// needle in a set of config files. This is intended to be
+/// used as a low-cost way of enabling Kubernetes ingress
+/// using nginx running on a machine that has a public port.
+/// 
+/// The needle is expected to be a dummy IP address; something
+/// fairly unique. The goal is to replace nginx files, where
+/// we often repeat lines if we want nginx to load balance between
+/// multiple destination IPs.
 #[derive(Parser, Debug)]
 #[command(version, about, long_about = None)]
 struct Args {