The design described what the host does and never what it is at runtime. The
words daemon, long-running, interval, poll and heartbeat appeared nowhere in it
or in the relevant decisions. What exists is a command that runs and exits;
what the design needs is a process holding a link. Nobody had written down that
those differ, so several questions had no answer.
0057 settles them. It runs on every node -- the host is what makes a machine
managed, so a machine without one is not a node. Root, because no useful subset
of the job is unprivileged. A systemd unit, because something must survive a
reboot to hold the link.
It never manages its own unit. The temptation is obvious and it ends with a
host stopping itself half way through an apply, leaving a machine with nothing
running to fix it. The installation owns the host; the host owns everything
else.
Installed as a package, with a tarball as the floor. The package carries the
unit file, the state directory and an upgrade path, which a bare binary does
not. But the mesh's package repository is hosted on the mesh, so any route that
needs the mesh to install the thing that joins the mesh is a circle -- the
tarball is the path that must never acquire a dependency.
Reconciles on start, on a declaration, on a timer and on reconnect. The timer
is the one easy to leave out, and without it `owned` reports what the host
applied rather than what is there -- ADR 0035 violated by omission.
The records checker caught this commit on its first attempt: 05 listed 0057 in
its frontmatter while 0057 is still proposed, and a to-be document may not rest
on an unaccepted record. The section now says so in the body instead.
