Your article was of interest in that you appeared to successfully contact redis via a subdomain, rather than just hostname.local. Although this appears to have nothing to do with your configuration as ping test.$(hostname).local is unsuccessful.

Upon further inspection, there is no mention of mdns on that redis DockerHub images page.. Their usage of .local appears to be invalid?

Your modification to /etc/nsswitch.conf omits the [NOTFOUND=return] entry that should be between mdns4 and dns. So while your /etc/mdns.allow file will enable mdns4 to attempt to resolve the *.local address over mDNS, should it fail, it will fallback to dns where it appears to resolve successfully. I have not verified myself, but removing mdns4 would likely result in the same outcome you blog about, where your actual issue was mdns rejecting non-compliant queries(technically it should only be the hostname, no additonal labels in the FQDN).