Support for systemd-resolved?

[Hoeze]

Hi, is there support for systemd-resolved?

We are using FreeIPA DNS with mutliple replicates. However, when the primary server goes offline, DNS is awfully slow.

systemd-resolved is able to remember currently working DNS servers. Therefore, we'd like to use it in conjunction with NetworkManager.

[thom311]

On your system you need to setup the various parts of DNS to work together. For example, to enable and use systemd-resolved, you possibly need:

• update nsswitch.conf to use "resolve"
• symlink /etc/resolv.conf to one of the well-known systemd-resolved files (see man systemd-resolved).
• possibly tell NetworkManager to use systemd-resolved (via "dns" and "rc-manager" setting in man NetworkManager.conf). But if you setup the symlink, that gets detected automatically
• enable and run systemd-resolved.

Here I don't mean that you need to configure a certain DNS nameserver or search domain. For that you can use the network role and NetworkManager already. I mean, you first need to configure the underlying parts how name resolution works in principle and to use systemd-resolved.

The network roles does not configure your system in that regard (yet). And it seems out of scope. What exactly would you expect the network role to do here?

[Hoeze]

Thanks for your answer @thom311. On Centos 8, I set dns=systemd-resolved inside NetworkManager.conf and I got the expected "nameserver 127.0.0.53" in the resolv.conf. DNS resolution still works.

If this is all what is required to enable systemd-resolved it would be nice to have a variable like dns_provider: systemd-resolved that is recognized during the NetworkManager configuration.

[thom311]

On Centos 8, I set dns=systemd-resolved inside NetworkManager.conf and I got the expected "nameserver 127.0.0.53" in the resolv.conf. DNS resolution still works.

Yes, you can do that, and that may be a sensible configuration.

but I think it's better to symlink /etc/resolv.conf to one of the well-known files like /run/systemd/resolve/stub-resolv.conf (read man systemd-resolved). If you do that, then you don't need any dns= or rc-manager= configuration in NetworkManager.conf, because by default NetworkManager would look at /etc/resolv.conf and automatically understand to use systemd-resolved.

All you need after changing that is systemctl reload NetworkManager.service.

So, to enable systemd-resolved via ansible you could do a few things:

• call ln -snf /run/systemd/resolve/stub-resolv.conf /etc/resolv.conf
• call systemctl enable --now systemd-resolved.service
• call systemctl reload NetworkManager.service.
• I guess you also need to configure /etc/nsswitch.conf somehow to use resolve. What the desired setting should be, depends on your preferences, which makes it hard to have a simple dns_provider: systemd-resolved.

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The role could provide something like dns_provider. But there are so many options what a user might want to do, that it seems hard to provide a sensible API of what is configurable. But yeah, maybe a nice feature!! Patches welcome :)

[liangwen12year]

This issue seems to be stale and is a duplicate of the issue https://github.com/linux-system-roles/network/issues/622, let us close it.