I’m not sure if this is an intermittent problem, or a permanent change in URL.
doc/howto/images_remote.md and doc/reference/image_servers.md both link to https://git.launchpad.net/simplestreams/tree/, but that URL gives a 503 for me.
It’s weird, because git clone https://git.launchpad.net/simplestreams works fine. There’s something about a request from a regular browser it doesn’t like.
Pretty sure the link is still meant to be good. I remember looking into an automated report of the broken link and when you go to https://launchpad.net you can definitely find your way to the same broken URL.
So it’s likely just a temporary (for a few weeks now) breakage on the Launchpad infrastructure…