This is a simple server that responds with the http headers it received. Image versions >= 1.4 removes the redirect introduced in 1.3. Image versions >= 1.3 redirect requests on :80 with X-Forwarded-Proto: http to :443. Image versions > 1.0 run an nginx server, and implement the echoserver using lua in the nginx config. Image versions <= 1.0 run a python http server instead of nginx, and don't redirect any requests.