Add socket activation support for systemd

[davidstrauss]

Reasons it's awesome:

• Better dependency management at boot time. Especially for pdns-recursor, many services may need to connect to run properly. Socket activation allows systemd to open the socket in early boot, allowing services depending on pdns or pdns-recursor to start in parallel.
• More secure isolation. Nothing needs to start as root because systemd handles the initial listening on a low port and passes it into the daemon. With network namespaces, daemons can run in containers isolating them from unnecessary network access, in or out. Passed-in sockets still work.
• On-demand service start-up, if desired.
• Restarting and reconfiguring the service don't interrupt listening.
• More consistent listener configuration relative to other services using socket activation.

Some C-based examples are here: http://0pointer.de/blog/projects/socket-activation.html

[bjoe2k4]

Any update on this? Using the recursor is quite a pain if other services depend on it.

[cmouse]

Can't you workaround with After=pdns-recursor.service?

[bjoe2k4]

Yes, this is what i ended up doing (actually After=nss-lookup.target), but you have to do it for every service that requires dns lookups on startup. Still, socket activation would be nice to have.