[PATCH pve-manager] api: nodes: dns: restart postfix after changing name servers

[Jonas Theisen <j.theisen@proxmox.com>]

Postfix runs its SMTP client in a chroot and copies /etc/resolv.conf
into it only when the instance starts. A running postfix therefore
keeps using the old name servers after a DNS settings change,
which can make mail delivery fail until the next restart.

Restart the postfix service after writing the new settings, but only
if it is currently active.
A failed restart only warns, since the DNS settings were already
written.

Came up in: https://forum.proxmox.com/threads/187442

Signed-off-by: Jonas Theisen <j.theisen@proxmox.com>
---
 PVE/API2/Nodes.pm | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/PVE/API2/Nodes.pm b/PVE/API2/Nodes.pm
index df0b2c2d..35078d3b 100644
--- a/PVE/API2/Nodes.pm
+++ b/PVE/API2/Nodes.pm
@@ -1671,6 +1671,17 @@ __PACKAGE__->register_method({
 
         PVE::INotify::update_file('resolvconf', $param);
 
+        # postfix copies resolv.conf into its chroot only on start, so a running instance needs a
+        # restart to use the new name servers
+        eval {
+            my $active = PVE::Tools::run_command(
+                ['systemctl', 'is-active', '--quiet', 'postfix@-'],
+                noerr => 1,
+            );
+            PVE::Tools::run_command(['systemctl', 'restart', 'postfix@-']) if $active == 0;
+        };
+        warn "failed to restart postfix - $@" if $@;
+
         return;
     },
 });
-- 
2.47.3