It reported "N machines run an older host than another" by comparing
versions as strings. A host reports its version as a commit, and commits
have no order. On the live mesh it named the three machines running the
NEWER host as the ones behind — ced54d4 sorts above 04a27ca and that is
all it means.
The code even carried a caveat saying versions compare as strings and that
this "is enough for the timestamps and commits this mesh uses". That was
the error, written down and not noticed: enough for timestamps, meaningless
for commits, and the mesh reports commits.
It now reports the split and claims no ordering, which is more useful as
well as more honest — the reader sees who is on which side, and that is
what decides whether a field can be sent. Ordering is left with the host,
which would have to report something ordered for anybody to have it.
This is issue 145 arriving by my own door an hour after I closed it: a
report that confidently says the opposite of the truth is worse than one
that says less.
Measured live. All four machines run the identical host binary — same
digest, installed within eighteen seconds — and at first only one reported
a version, which read as a difference where there was none.
A machine publishes a report after an apply. The five-minute reconcile
publishes nothing, because it is the machine keeping itself as declared
rather than answering anything. So a current, idle machine never says, and
the mesh cannot tell that from a machine running something ancient.
Confirmed by pushing: not reported, then 04a27ca.
Enough for the purpose, not enough for the claim. For deciding whether a
new declaration field is safe it is sufficient — pushing is what the mesh
is about to do, and the answer arrives with the act. For knowing what the
mesh runs it is not, and "not reported" is worded as "nobody has asked
recently" for that reason.
Making a heartbeat carry it would close the gap and would change what a
heartbeat is — a bare word that the node is there, deliberately carrying
nothing else. Left alone rather than widened in passing.
The machine has reported its host version since ADR 0141, whose own
comment says why it must: without it nothing can say a machine is behind.
The controller's copy of the report did not have the field, so it
unmarshalled into nothing and was thrown away on arrival. Two structs
describe one message and only the sending side had it.
node show names it per machine, "not reported" where the mesh has not been
told. status names every machine running an older host than another does,
and which is newest.
Disagreement rather than staleness, deliberately: nothing delivers a host
version yet, so the mesh holds no canonical current one and "behind" has
no fixed point. What it can say is that the oldest host in the mesh is
what the mesh may send.
Two refusals to guess: a machine that reported nothing is not called
behind, and versions compare as strings — right for the timestamps this
mesh uses, wrong for a scheme where 10 sorts before 9, said at the place
that would have to learn.
107 gains the note that this is what makes its new field safe to consider,
and that one machine of four is behind today, so it is not free yet.
jschoubben