Systemd-based socket activation

[schaten]

• Version of iperf3 (or development branch, such as master or
  3.1-STABLE) to which this pull request applies: master

• Issues fixed (if any): enhancement: systemd socket activation, service and target files #742

• Brief description of code changes (suitable for use as a commit message): Allow iperf3 to receive sockets from systemd.

This patch enables systemd-based socket activation of iperf3. To test, build and install this fork, then:

• mv contrib/iperf3_@.* /etc/systemd/system/
• systemctl daemon-reload
• systemctl start iperf3_5201

This will make systemd listen on port 5201. As soon as a client tries to connect, iperf3 is started and takes over.

I originally wanted to add multi-user support, but this is not as easy due to the separate control / data connections.
In combination with loadbalancing (i.e. based on the IP address, client could be NATted to a socket-activated iperf3 instance) it might still be useful..
Also, as the socket-activation was a separate issue, maybe it's useful to others. :)

[gharris999]

This is very helpful. Absent multiple simultaneous client support in iperf3, this allows me to have systemd monitor, say, 24 ports and dynamically launch one-off iperf3 servers to service client requests on those ports. I've built iperf3 from schaten's fork and it works perfectly. It took me a bit to realize that libsystemd-dev was a dependency. I guess that should have been obvious.

Edit: I think schaten's fork requires libsystemd-dev > version 237 in order to work. I.e. won't work on Ubuntu 18.04, but works fine on Ubuntu 20.04 which has version 245.

[friesen-hbk]

Cool! Yes, it's very helpful!

[mikelpr]

what's blocking the merge of this?

[eriksjolund]

@schaten Thanks for implementing this functionality!

I would like to use a current esnet:master (https://github.com/esnet/iperf/commits/master/) with the socket activation functionality added. To achieve that I created a git merge commit
eriksjolund@807d33e
in
https://github.com/eriksjolund/iperf/tree/support-socket-activation

I don't know how to properly do git merges, especially the question of which name to write for author. I hope I got it right.
Anyway, a better solution would be to rebase schaten:master on to esnet:master

@schaten could you rebase on to esnet:master and resolve the trivial conflicts?

[schaten]

Glad to hear this was useful. Thanks everyone. :)
I rebased the branch. Maybe someone (@bmah888) is interested in merging it.

Somehow it took me way too long to test it afterwards, because of the following things. Leaving it here as a reference:

• Don't forget to regenerate the configure script by running autoconf... Probably very obvious but I don't use autotools so often. The configure script in the git repo should be updated before merging this also. I didn't include that because it changes other stuff that seems unrelated.
• The socket is started with systemctl start iperf3_@5201.socket (note the '@'), sorry I got this wrong in the initial post here.
• In the service file under the Unit section, the line Environment=LD_LIBRARY_PATH=/usr/local/lib might be needed if iperf was installed manually with sudo make install.
• Install libsystemd-dev before building, as @gharris999 mentioned.