What does fwd mean in the heroku logs?

Question

Inside the heroku logs, I have the following line...

Aug 06 21:50:18 coolApp heroku/router:  at=info method=GET path="/about.jpg" host=coolapp.com fwd="78.7.88.177,643.198.55.55" dyno=web.1 connect=0ms service=43ms status=500 bytes=420 

My question is what does fwd represent? I see they are IP addresses. Are they IP addresses from the user?

Homebody

Answer 1

From heroku docs:

fwd: HTTP request X-Forwarded-For header value

From Wikipedia:

The X-Forwarded-For (XFF) HTTP header field is a common method for identifying the originating IP address of a client connecting to a web server through an HTTP proxy or load balancer.

So I think you are right when the http requests are from a user's browser.

Linguistician

while the docs don't specify it, this is the header value that is SENT to the downstream application, not the header value that is received by Heroku. this means that the header also includes the IP address of the client that connected to Heroku. if you want to dive in real deep on this topic, I recommend: adam-p.ca/blog/2022/03/x-forwarded-for – Karlenekarlens