Configure Flask dev server to be visible across the network

I’m not sure if this is Flask specific, but when I run an app in dev mode (http://localhost:5000), I cannot access it from other machines on the network (with http://[dev-host-ip]:5000). With Rails in dev mode, for example, it works fine. I couldn’t find any docs regarding the Flask dev server configuration. Any idea what should be configured to enable this?

X-Forwarded-Proto and Flask

I have precisely the same problem described in this SO question and answer. The answer to that question is a nice work around but I don’t understand the fundamental problem. Terminating SSL at the load balancer and using HTTP between the load balancer and web/app servers is very common. What piece of the stack is not respecting the X-Forwarded-Proto? Is it werkzeug? Flask? uwsgi?