It has been reported that at least one png image fails to load with ERR_CONTENT_DECODING_FAILED: https://upload.wikimedia.org/wikipedia/commons/thumb/4/49/Relief_map_of_Serbia.png/272px-Relief_map_of_Serbia.png in esams. All esams frontend are affected, the object is cached on cp3037's varnish-be.
The error is due to the fact that the image is not compressed, but the response contains Content-Encoding: gzip.
curl --compressed fails with the following message:
curl: (61) Error while processing content unencoding: invalid stored block lengths
Most likely, the problem is not related to esams-specific network conditions. esams is probably just the DC that happened to cache a bad copy.
It is not clear why we try to gzip pngs at all, even if the browser accepts gzip.
Using curl --compressed against vanrnish-be works fine.