HomeAssistant OS can't resolve local hostname

CentralCommand · December 8, 2022, 1:58pm

Going to quote myself from one of the threads you linked

One possibility I would like to check if you don’t mind (should be quick). Most of the containers used in a typical home assistant deployment are alpine based which means they use musl rather then glibc. This has an interesting consequence when it comes to DNS because of this commit . According to the DNS spec if a host exists a DNS server should always return NOERROR, even if they have no answers for the particular type of query (like if a host has only an ipv4 address but not an ipv6 one). musl enforces this, glibc does not. Because musl and alpine is newer not all DNS servers respect this rule and as a result unexpected NXDOMAINS can be encountered on alpine based systems.

We set up a simple test to check for this and are going to start testing DNS servers for this so we can let users know if their DNS server has an issue once this PR is merged. In the meantime you can test this manually by using the test domain we set up that only resolves for A type queries by doing this:
dig _checkdns.home-assistant.io A +noall +comments
dig _checkdns.home-assistant.io AAAA +noall +comments
Your response should have status: NOERROR for both of those, like this:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 6899
If not then that may be the issue. Since a query issued for a type not supported by one of your local domains could be getting back an NXDOMAIN and causing the DNS plugin (which is alpine based) to think the entire domain doesn’t exist. Home Assistant too since it is also alpine based.

This is the problem. You can see it in the output of the first command. Your DNS server is returning an answer for an A request for test.lab.lan but is returning NXDOMAIN for the follow-up AAAA request on that domain (ipv6).

This means your DNS server is not following DNS spec correctly. DNS servers are only supposed to return NXDOMAIN if the name truly does not exist for all types of queries. If it exists but there are no answers for some types of queries (like say because you don’t use ipv6) then it should return a NOERROR response without any answers.

Alpine based systems like HA require DNS servers follow the DNS spec in this regard for the reasons I mentioned above. If your DNS server returns NXDOMAIN for any queries on a name then HA, most of HAs addons and any other Alpine based systems will assume the name does not exist for all queries.