So, what's a 499 status code?
What exactly is an HTTP 499 status code? You'll find a variety of answers online, but unfortunately, most of them are incorrect. Oddly enough, the internet can get things wrong! But don't worry, today I'm going to clear up the confusion for you. So, what's a 499 status code? Simply put, it's when a client sends a FIN (finish) to NGINX before it has a chance to respond. Let me paint you a picture using the context of a 200 HTTP OK status. When a client connects, it sends an HTTP request (for example, a "/something") to an API endpoint. This could either be to fetch a file or to get JSON data back from a database. So here's the process: The client sends a request. NGINX transfers that request to an upstream entity, which is usually a Node.js running Express, along with some Mongo in a database. It fetches the data and sends a response back to the client who then receives it. This is known as a 200 status and is the ideal scenario. However, there's one condition under which NGINX will produce a 499 status. It looks like this: The client sends their request as usual. NGINX forwards that request to your NGINX upstream (in this case, Node.js). But then your client aborts the request before a response comes in. This triggers the 499 status. This is the only scenario when NGINX logs a 499, which you need to monitor, and we'll delve further into this later.
