nixos/systemd: fix NSS database ordering

- The order of NSS (host) modules has been brought in line with upstream
  recommendations:

  - The `myhostname` module is placed before the `resolve` (optional) and `dns`
    entries, but after `file` (to allow overriding via `/etc/hosts` /
    `networking.extraHosts`, and prevent ISPs with catchall-DNS resolvers from
    hijacking `.localhost` domains)
  - The `mymachines` module, which provides hostname resolution for local
    containers (registered with `systemd-machined`) is placed to the front, to
    make sure its mappings are preferred over other resolvers.
  - If systemd-networkd is enabled, the `resolve` module is placed before
    `files` and `myhostname`, as it provides the same logic internally, with
    caching.
  - The `mdns(_minimal)` module has been updated to the new priorities.

  If you use your own NSS host modules, make sure to update your priorities
  according to these rules:

  - NSS modules which should be queried before `resolved` DNS resolution should
    use mkBefore.
  - NSS modules which should be queried after `resolved`, `files` and
    `myhostname`, but before `dns` should use the default priority
  - NSS modules which should come after `dns` should use mkAfter.

1 files changed, 71 insertions, 0 deletions

diff --git a/nixos/doc/manual/from_md/release-notes/rl-2111.section.xml b/nixos/doc/manual/from_md/release-notes/rl-2111.section.xml
index fcaac9e8bec..e923a289442 100644
--- a/nixos/doc/manual/from_md/release-notes/rl-2111.section.xml
+++ b/nixos/doc/manual/from_md/release-notes/rl-2111.section.xml
@@ -562,6 +562,77 @@
           be removed in 22.05.
         </para>
       </listitem>
+      <listitem>
+        <para>
+          The order of NSS (host) modules has been brought in line with
+          upstream recommendations:
+        </para>
+        <itemizedlist spacing="compact">
+          <listitem>
+            <para>
+              The <literal>myhostname</literal> module is placed before
+              the <literal>resolve</literal> (optional) and
+              <literal>dns</literal> entries, but after
+              <literal>file</literal> (to allow overriding via
+              <literal>/etc/hosts</literal> /
+              <literal>networking.extraHosts</literal>, and prevent ISPs
+              with catchall-DNS resolvers from hijacking
+              <literal>.localhost</literal> domains)
+            </para>
+          </listitem>
+          <listitem>
+            <para>
+              The <literal>mymachines</literal> module, which provides
+              hostname resolution for local containers (registered with
+              <literal>systemd-machined</literal>) is placed to the
+              front, to make sure its mappings are preferred over other
+              resolvers.
+            </para>
+          </listitem>
+          <listitem>
+            <para>
+              If systemd-networkd is enabled, the
+              <literal>resolve</literal> module is placed before
+              <literal>files</literal> and
+              <literal>myhostname</literal>, as it provides the same
+              logic internally, with caching.
+            </para>
+          </listitem>
+          <listitem>
+            <para>
+              The <literal>mdns(_minimal)</literal> module has been
+              updated to the new priorities.
+            </para>
+          </listitem>
+        </itemizedlist>
+        <para>
+          If you use your own NSS host modules, make sure to update your
+          priorities according to these rules:
+        </para>
+        <itemizedlist spacing="compact">
+          <listitem>
+            <para>
+              NSS modules which should be queried before
+              <literal>resolved</literal> DNS resolution should use
+              mkBefore.
+            </para>
+          </listitem>
+          <listitem>
+            <para>
+              NSS modules which should be queried after
+              <literal>resolved</literal>, <literal>files</literal> and
+              <literal>myhostname</literal>, but before
+              <literal>dns</literal> should use the default priority
+            </para>
+          </listitem>
+          <listitem>
+            <para>
+              NSS modules which should come after <literal>dns</literal>
+              should use mkAfter.
+            </para>
+          </listitem>
+        </itemizedlist>
+      </listitem>
     </itemizedlist>
   </section>
 </section>