A few days ago systemd gained tools which allow you to monitor Varlink traffic. A new Varlink service (io.systemd.VarlinkMonitor) allows you to set up a ring buffer which will get filled with packets containing the traffic which matches the filters you provide. This provides the functionality that org.freedesktop.DBus.Monitoring provides for D-Bus. A new varlinkctl monitor verb allows you to use this feature in terminals and scripts. This provides the functionality that dbus-monitor provides for D-Bus and uses io.systemd.VarlinkMonitor under the hood. If you pass --json short to varlinkctl monitor, it produces JSON-seq which can be passed into jq --seq to further process the captured data.

I presented this in the broader context of observability with Varlink at All Systems Go. Slides and video of the talk are available online.

This is a good start, but I think we should add more tooling around it. Especially Bustle would be an interesting target because it would allow us to capture D-Bus and Varlink at the same time and get a global view of what is going on in our systems again.