Build a Real-Time ISS Tracker with Quarkus, SSE, and Qute

Most developers look at a small real-time app like this and think it is mainly a frontend exercise. Poll an API, move an icon on a map, done. That works for a demo, but it breaks down fast when you turn it into an actual service. Browsers start polling too often, upstream calls pile up, your server does duplicate work for every tab, and one slow public API drags the whole thing down. The better mental model is this: the browser is not the source of truth. Your Quarkus service is. It owns the upstream HTTP call, it decides how often data gets refreshed, it caches the latest good result, and it pushes updates to every connected client. That gives you one polling loop, one failure boundary, and one place to harden behavior when the upstream service is slow or unavailable. This matters even in a small tutorial. Public APIs fail. Network calls stall. Frontends reconnect. SSE clients disappear without warning. If you do not put the right boundaries in place, a harmless little tracker turns i