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I have yet to understand why we want systemd to take over DNS lookups in the first place, and honestly fallback servers are of debatable value. I personally wo

I have yet to understand why we want systemd to take over DNS lookups in the first place, and honestly fallback servers are of debatable value. I personally would prefer to configure fallback servers explicitly, especially since there are cases where the fallback servers could be problematic (e.g. if you are using HE's tunnelbroker service and need to selectively block AAAA records for Netflix; the fallback servers will not do this, and systemd could unexpectedly switch to the fallback servers). Obviously others like the behavior and were surprised when it stopped working as expected.

SAI_Peregrinus 6y ago
Systemd is a project to create a unified architecture for all system daemons. The various daemons plug in to systemd via its apis (dmesg, etc) and can all be managed through the same mechanisms (unit files, systemctl, etc). If we want DNS lookups to be managed by a system daemon, then it makes sense for systemd to provide such a daemon. Fallback servers can be explicitly configured via a configuration file. Systemd provided default fallback servers, if none were set in the config file. IIUC the config file having fallback servers set would prevent the default fallbacks from being used, even if the config file servers weren't responding.
- betterunix2 6y ago
  That all sounds very counterintuitive. The "fallback" amounts to a statically configured list of DNS servers, separate from the other lists of statically configured DNS servers, with the property that if no DNS servers were explicitly configured by any method the systemd developers assume DNS servers will be configured by then the system will use the DNS servers that systemd developers thought were a good idea to use. Not only is it complicated and brittle, it also is not clear why a project that intends "to create a unified architecture for all system daemons" is rewriting the rules of how DNS servers are configured. For that matter, why is this logic (which is of questionable value) in systemd instead of NetworkManager (which already deals with DNS server configuration and is user-facing and better able to inform users that the fallbacks are being used)?

SAI_Peregrinus 6y ago

Systemd is a project to create a unified architecture for all system daemons. The various daemons plug in to systemd via its apis (dmesg, etc) and can all be managed through the same mechanisms (unit files, systemctl, etc). If we want DNS lookups to be managed by a system daemon, then it makes sense for systemd to provide such a daemon. Fallback servers can be explicitly configured via a configuration file. Systemd provided default fallback servers, if none were set in the config file. IIUC the config file having fallback servers set would prevent the default fallbacks from being used, even if the config file servers weren't responding.

betterunix2 6y ago
That all sounds very counterintuitive. The "fallback" amounts to a statically configured list of DNS servers, separate from the other lists of statically configured DNS servers, with the property that if no DNS servers were explicitly configured by any method the systemd developers assume DNS servers will be configured by then the system will use the DNS servers that systemd developers thought were a good idea to use. Not only is it complicated and brittle, it also is not clear why a project that intends "to create a unified architecture for all system daemons" is rewriting the rules of how DNS servers are configured. For that matter, why is this logic (which is of questionable value) in systemd instead of NetworkManager (which already deals with DNS server configuration and is user-facing and better able to inform users that the fallbacks are being used)?