Varnish won't start because backend host resolves to too many addresses, but they are all identical IPs

Batanun B batanun at hotmail.com
Wed Apr 19 08:48:02 UTC 2023


All of the sudden Varnish fails to start in my development environment, and gives me the following error message:

Message from VCC-compiler:
Backend host "redacted-hostname": resolves to too many addresses.
Only one IPv4 and one IPv6 are allowed.
Please specify which exact address you want to use, we found all of these:
     555.123.123.3:80
     555.123.123.3:80
     555.123.123.3:80

I have changed the hostname and the IP above to not expose our server, but all three IP numbers are 100% identical. Shouldn't Varnish be able to figure out that in that case it can just choose any one and it will work as expected? It really should remove duplicates, and only if there are more than one non-duplicate IP then it should fail.

The problem is that the backend host is a so called "app service" in Microsoft Azure, which is basically a platform as a service (PaaS), where Microsoft handles the networking including the domain name (no user access it directly). I have no idea why it suddenly resolves to multiple duplicate IPs.
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