Files
hq/04-ISSUES/024-a-lab-run-stalls-before-the-host-is-placed/00-report.md
T
jschoubben f6b1834ea9 024 fixed — the registry was addressed by hand and nothing else was
The cause was one line. Machines get a systemd-networkd unit with a
static address, so networkd finishes and reports the link configured.
The registry ran `ip addr add` inline, which leaves networkd waiting to
configure something it was never told about — and
systemd-networkd-wait-online has an infinite timeout.

So network-online.target was never reached and everything ordered after
it never started. On these machines that is Docker, so `docker load`
blocked on a socket whose daemon was queued behind a target that would
never come, and three bounded timeouts stacked to thirty-five minutes.
These machines have no DHCP by design, so that wait was never going to
end.

The hypothesis in this record was wrong and the record now says so.
Stocking had just been changed, so stocking looked guilty; stocking
takes 34 seconds and always did, timed directly before changing
anything.

Fixed with two things that made it cost hours instead of minutes: an
image placement now waits for the runtime and refuses after 120s naming
what systemd is waiting on, and the end-to-end test passes onProgress —
the raise reported every step and the test discarded it, which is why
thirty-five minutes and four minutes of silence looked the same.

The suite then ran to completion, 23 of 24, the one failure a check of
its own flagging a path as a credential because `/` is in the base64
alphabet.

Also recorded: a redirected log lags, because Node block-buffers stdout
to a file. Read as a stall twice, the second time right after the real
fix — where a buffering artifact argues the fix did not work.
2026-09-01 09:53:08 +02:00

5.1 KiB

status, opened, located-in, fixed-by, amended-design
status opened located-in fixed-by amended-design
fixed 2026-09-01
mesh-lab
mesh-lab 3503ad9

024 — A run stalls before the host is placed, and says nothing while it does

Symptom

The first scenario of the end-to-end suite raises its machines and then stops. Observed twice on 2026-09-01, both times after the rebuild step grew:

  • Once mid-run, during the rotation test: the suite had reported thirteen passes, then the process ended with no summary, no failure and no receipt.
  • Once from the start: a bare machine becomes a mesh ran for 35 minutes against a measured 4.5, produced no output at all, and was still running when it was stopped by hand.

Both machines were RUNNING throughout. The second one was interrogated directly: the anchor VM answered, and had no mesh-host log and no containers — so the run had not reached placing the host. It was stuck earlier, in stocking the scenario's registry.

What is not the cause

  • Not memory. 84 GiB available, no OOM in the kernel log.
  • Not the daemon. incus exec into the stalled machine answered immediately.
  • Not the changes under test. The credential work is applied after the host is placed, and the host was never placed.

What changed just before — and it was not the cause

The rebuild step had gone from two artifacts to six, and every image is pushed into the scenario's registry, which looked like where the stall sat. That was written down as a coincidence rather than a diagnosis, and it is as well: stocking takes 34 seconds and always did. Timed directly, eight images, before anything was changed.

The suspicion was the ordinary kind — the thing that changed most recently looks guilty — and the thing that changed had nothing to do with it.

Why it matters more than a slow test

A stall is indistinguishable from work. The suite prints nothing between starting a scenario and finishing its first test, so four and a half minutes and thirty-five look identical from the outside — and the operator's only recourse is to guess, which is precisely how a workstation was left unbootable in August by killing a package manager that was working.

The first stall is worse: the process ended silently after thirteen passes. No summary, no receipt, nothing that says the run was cut short. A run that stops without saying so is a run somebody may believe.

What a fix has to give

  • Progress while stocking, so a long step is visibly a long step. Bytes moved, images pushed, anything that changes.
  • A receipt when a run is cut short, saying how far it got. lastrun already refuses to guess; what is missing is it being written at all when the process dies mid-run.
  • A stated timeout on stocking, so a stall ends as a failure with a reason rather than as a process somebody eventually kills.

The cause

The registry machine was addressed by hand and every other machine was not.

Machines get a systemd-networkd unit with a static Address=, so networkd finishes configuring the link and reports it configured. The registry instead ran ip addr add inline. An address put on a link that way leaves networkd still waiting to configure something it was never told about, so the link sits at configuring — and systemd-networkd-wait-online has TimeoutStartUSec=infinity.

So network-online.target is never reached, and everything ordered after it never starts. On these machines that is Docker. docker load then blocks on a socket whose daemon is queued behind a target that will never come, and the three bounded timeouts around it — save, push, load — stack to thirty-five minutes.

Measured on one scenario, before and after:

before after
the registry's link configuring configured
docker.service inactive, 5 jobs pending active, no jobs
the raise never finished 87.5 s

These machines have no DHCP by design — a scenario is a closed address space and the declaration owns the addresses — so nothing was ever going to complete that wait.

Fixed

  • The registry is addressed the way every other machine is, through the same helper.
  • Placing an image waits for the container runtime and refuses after 120s, naming what systemd is still waiting on. A stall becomes a failure that says why.
  • The end-to-end test passes onProgress. The raise reported every step and the test threw it away, which is why thirty-five minutes of silence and four minutes of silence looked the same.

The suite then ran to completion: 23 of 24, the one failure a check of its own that flagged /var/lib/mesh/builder/broker as a credential because / is in the base64 alphabet. Fixed with it.

Also learned, at some cost

A redirected log lags. Node block-buffers stdout when it is a file, so > run.log sits unchanged for minutes while the run is fine. That was read as a stall twice — the second time immediately after the real fix, where a buffering artifact argues the fix did not work. The machines answer instantly and are the source of truth. "I cannot see progress" is not evidence of no progress.