Doc: Better DNS persistence solution for systemd #14589

kkovacs · 2024-12-05T17:47:37Z

Amended documentation with a better way to setup DNS-resolving LXD containers from the host machine.

This is a re-submit of #14572 .

kkovacs · 2024-12-05T17:50:31Z

Hi @simondeziel and @tomponline , I've re-submitted the PR as you asked.

I've added information regarding the situation Simon has encountered, and also opened #14588 , because lxdbr0 not being in a managed state is an issue that needs to be handled separately, not in this documentation snippet (even if I've added a workaround here).

simondeziel · 2024-12-05T19:49:57Z

@kkovacs If the existing .service hack doesn't work reliably on its own we might need to add something (udev rules?) to restart the service whenever the network device itself is changed.

kkovacs · 2024-12-05T20:10:16Z

I'm not very familiar with udev configuration. :) The .network file should be the correct solution IMHO; the one-shot service – even if somehow fortified by udev rules – is many more "rubber balls" on each other, and feels more hack-ish.

The .network solution is robust, and it would work immediately if the bridge was not out of sight for systemd-networkd after install. This temporary situation could easily cause other issues too, which are yet unknown.

But of course, it's up to the LXD project how to do this. I would be most happier if resolving the lxd-container-name.lxd names from the host would just work out of the box, and would not need a post-install snippet :)

doc/howto/network_bridge_resolved.md

tomponline · 2024-12-09T16:38:36Z

Please sign the CLA https://ubuntu.com/legal/contributors/agreement

tomponline · 2024-12-09T16:39:07Z

Please can you also rebase as main has fixes for some linter issues that are blocking the tests.

kkovacs · 2024-12-09T21:00:39Z

Please sign the CLA

I did!

Please can you also rebase as main has fixes for some linter issues that are blocking the tests.

I did :)

doc/howto/network_bridge_resolved.md

tomponline

Please can you sign off your commits.

See https://github.com/canonical/lxd/blob/main/CONTRIBUTING.md#developer-certificate-of-origin

tomponline · 2024-12-10T10:08:32Z

The CLA check is failing with

user@kk-e1 ✕ (has no Launchpad account)

…ntainers from the host machine. Signed-off-by: Kristof Kovacs <[email protected]>

kkovacs · 2024-12-10T16:30:36Z

Signed off, removed "apparently", fixed "author", rebased, pushed. Fingers crossed. :)

tomponline · 2024-12-10T16:34:14Z

DCO and CLA check are good :)

tomponline · 2024-12-10T16:43:48Z

@minaelee happy with this?

doc/howto/network_bridge_resolved.md

Co-authored-by: Minae Lee <[email protected]> Signed-off-by: K Kovács <[email protected]>

kkovacs · 2024-12-11T17:59:21Z

Thank you @minaelee! It's incredible how much clearer you have made the text. Kudos!

minaelee · 2024-12-11T19:38:11Z

doc/howto/network_bridge_resolved.md

@@ -72,7 +72,70 @@ You must repeat the commands after each reboot and after LXD is restarted, or ma

 You can automate the `systemd-resolved` DNS configuration, so that it is applied on system start and takes effect when LXD creates the network interface.


Suggested change

You can automate the `systemd-resolved` DNS configuration, so that it is applied on system start and takes effect when LXD creates the network interface.

This is repeated in line 75

minaelee · 2024-12-11T19:40:28Z

doc/howto/network_bridge_resolved.md

@@ -72,7 +72,70 @@ You must repeat the commands after each reboot and after LXD is restarted, or ma

 You can automate the `systemd-resolved` DNS configuration, so that it is applied on system start and takes effect when LXD creates the network interface.

-To do so, create a `systemd` unit file named `/etc/systemd/system/lxd-dns-<network_bridge>.service` with the following content:
+You can automate the systemd-resolved DNS configuration so that it is applied on system start and takes effect when LXD creates the network interface. To do so, there are two approaches you can take, detailed below. Use only one of the approaches.


Suggested change

You can automate the systemd-resolved DNS configuration so that it is applied on system start and takes effect when LXD creates the network interface. To do so, there are two approaches you can take, detailed below. Use only one of the approaches.

There are two approaches to automating `systemd-resolved` configuration to ensure that it persists when the LXD bridge network is re-created. Use only one of these approaches, described below.

minaelee · 2024-12-11T19:45:59Z

doc/howto/network_bridge_resolved.md

-To do so, create a `systemd` unit file named `/etc/systemd/system/lxd-dns-<network_bridge>.service` with the following content:
+You can automate the systemd-resolved DNS configuration so that it is applied on system start and takes effect when LXD creates the network interface. To do so, there are two approaches you can take, detailed below. Use only one of the approaches.
+
+The first approach is recommended as more resilient; it is reapplied if the lxdbr0 network is re-created at any point. For example, updating and restarting LXD can occasionally cause the lxdbr0 network to be recreated.


Suggested change

The first approach is recommended as more resilient; it is reapplied if the lxdbr0 network is re-created at any point. For example, updating and restarting LXD can occasionally cause the lxdbr0 network to be recreated.

The first approach is recommended because it is more resilient. It applies your desired configuration whenever your system is rebooted, _and_ whenever the LXD bridge network is re-created outside of a system reboot. For example, updating and restarting LXD can occasionally cause its bridge network to be re-created.

doc/howto/network_bridge_resolved.md

minaelee

Suggested updates based on this conversation, thanks!

minaelee · 2024-12-11T20:31:11Z

doc/howto/network_bridge_resolved.md

+
+The first approach is recommended as more resilient; it is reapplied if the lxdbr0 network is re-created at any point. For example, updating and restarting LXD can occasionally cause the lxdbr0 network to be recreated.
+
+If you are unable to use the recommended approach for some reason, the second alternative approach can be used. However, if the lxdbr0 network is re-created, you must reapply that solution manually.


Suggested change

If you are unable to use the recommended approach for some reason, the second alternative approach can be used. However, if the lxdbr0 network is re-created, you must reapply that solution manually.

If you are unable to use the recommended approach, the alternative approach can be used. The alternative approach applies your desired configuration only when your system is rebooted. If LXD re-creates its bridge network outside of a system reboot, you must reapply the configuration manually.

minaelee · 2024-12-11T20:35:05Z

doc/howto/network_bridge_resolved.md

+Domains=~<dns_domain>
+```
+
+So for example, `/etc/systemd/network/lxdbr0.network` with the following content (your IP, of course):


Suggested change

So for example, `/etc/systemd/network/lxdbr0.network` with the following content (your IP, of course):

Example file content for `/etc/systemd/network/lxdbr0.network` (insert your own DNS value):

minaelee · 2024-12-11T21:04:53Z

doc/howto/network_bridge_resolved.md

+```
+
+### Alternative approach
+


Suggested change

```{warning}

This approach only automates applying your desired configuration when your system is rebooted. If LXD re-creates its bridge network outside of a system reboot, you must reapply the configuration manually with the following command:

systemctl restart lxd-dns-<bridge_network>.service

Example:

systemctl restart lxd-dns-lxdbr0.service

```

github-actions bot added the Documentation Documentation needs updating label Dec 5, 2024

kkovacs marked this pull request as ready for review December 5, 2024 17:50

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tomponline requested a review from minaelee December 9, 2024 15:55

kkovacs force-pushed the documentation-systemd-dns-network branch from 50cc98f to cd26ca4 Compare December 9, 2024 21:00

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Amended documentation with a better way to setup DNS-resolving LXD co…

878d2a5

…ntainers from the host machine. Signed-off-by: Kristof Kovacs <[email protected]>

kkovacs force-pushed the documentation-systemd-dns-network branch from cd26ca4 to 878d2a5 Compare December 10, 2024 16:29

tomponline previously approved these changes Dec 10, 2024

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tomponline changed the title ~~Better DNS persistence solution for systemd (resubmit)~~ Doc: Better DNS persistence solution for systemd Dec 11, 2024

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Co-authored-by: Minae Lee <[email protected]> Signed-off-by: K Kovács <[email protected]>

kkovacs dismissed tomponline’s stale review via 2d5ee63 December 11, 2024 17:58

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Doc: Better DNS persistence solution for systemd #14589

Doc: Better DNS persistence solution for systemd #14589

kkovacs commented Dec 5, 2024

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		@@ -72,7 +72,70 @@ You must repeat the commands after each reboot and after LXD is restarted, or ma

		You can automate the `systemd-resolved` DNS configuration, so that it is applied on system start and takes effect when LXD creates the network interface.

	You can automate the systemd-resolved DNS configuration so that it is applied on system start and takes effect when LXD creates the network interface. To do so, there are two approaches you can take, detailed below. Use only one of the approaches.
	There are two approaches to automating `systemd-resolved` configuration to ensure that it persists when the LXD bridge network is re-created. Use only one of these approaches, described below.

	The first approach is recommended as more resilient; it is reapplied if the lxdbr0 network is re-created at any point. For example, updating and restarting LXD can occasionally cause the lxdbr0 network to be recreated.
	The first approach is recommended because it is more resilient. It applies your desired configuration whenever your system is rebooted, _and_ whenever the LXD bridge network is re-created outside of a system reboot. For example, updating and restarting LXD can occasionally cause its bridge network to be re-created.


		The first approach is recommended as more resilient; it is reapplied if the lxdbr0 network is re-created at any point. For example, updating and restarting LXD can occasionally cause the lxdbr0 network to be recreated.

		If you are unable to use the recommended approach for some reason, the second alternative approach can be used. However, if the lxdbr0 network is re-created, you must reapply that solution manually.

	So for example, `/etc/systemd/network/lxdbr0.network` with the following content (your IP, of course):
	Example file content for `/etc/systemd/network/lxdbr0.network` (insert your own DNS value):

+```{warning}
+This approach only automates applying your desired configuration when your system is rebooted. If LXD re-creates its bridge network outside of a system reboot, you must reapply the configuration manually with the following command:
+    systemctl restart lxd-dns-<bridge_network>.service
+Example:
+    systemctl restart lxd-dns-lxdbr0.service
+```

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