jschoubben
e88b448145
Snapshot 9.9s -> 0.13s. Restore 10.4s -> 0.80s. Three snapshots sharing 1.36 GB instead of costing 4.8 GB. The projected four-machine reset cycle falls from ~90s, unbounded at worst, to ~15s dominated by a boot that cannot be avoided. ADR 0029's inner-loop argument holds with copy-on-write and did not without it. The consistency matters as much as the speed: three consecutive snapshots took 0.13, 0.12 and 0.13 seconds, against a dir second snapshot that never finished. One honest counter-observation recorded: launching onto the fresh copy-on-write pool was slower, 20.2s against 14.3s, because the image had to be unpacked into a pool that had never seen it. Paid once per pool, and dwarfed by what snapshotting saves, but it went the other way. Doing the measurement produced the answer to how the lab installs on a clean machine, because both failure modes appeared while doing it. Installed is not available: the daemon was present with units disabled and no group. Issue 007. Available is not adequate, and this is worse: with the storage tooling absent everything worked and snapshots were seventy-six times slower. Nothing failed, nothing warned. That is a variant the mesh has not catalogued — its usual failure is reported success and did nothing; this is reported success and did it seventy-six times slower, which no error surface catches because nothing is wrong. So the lab verifies CAPABILITY, never installation, and refuses to run degraded rather than warning — a warning about a slow inner loop is read once and ignored forever. Prerequisites may arrive from a mesh module or from the lab's own bootstrap, and the second path is required rather than convenient: a lab installable only by a mesh cannot host the development of the mesh that installs it. The lab is the second thing installed by hand, after the node host, and for the same reason: something has to be first, and pretending otherwise produces a circularity papered over by a script nobody exercises.
6.3 KiB
layer, status, code, updated, decisions
| layer | status | code | updated | decisions | |||
|---|---|---|---|---|---|---|---|
| to-be | designed |
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2026-08-24 |
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Installing the lab on a clean machine
The lab has prerequisites — a virtualisation daemon, copy-on-write storage, a pool, an identity permitted to talk to it — and it cannot get them from the mesh, because it is where the mesh is built (ADR 0029).
So the lab needs an install path of its own. This describes it, and the shape it has to take is determined by two failures observed while measuring (research 010).
The two failures that shape this
One: installed is not available. The virtualisation package was present and explicitly
installed. Both its units were disabled, the operator was in no group, and the client reported
the server unreachable. Nothing had failed — the declaration was satisfied exactly as written
(04-ISSUES/007).
Two, and worse: available is not adequate. With the storage tooling absent, the daemon offered one driver, everything worked, and snapshots took seventy-six times longer than they needed to. Nothing failed. Nothing warned. A lab in that state runs correctly and is simply too slow to use — and the inner loop it exists to provide quietly does not exist.
The second is the more dangerous shape and it is a variant the mesh has not catalogued before. Its usual failure is reported success and did nothing. This is reported success and did it seventy-six times slower, which no error surface catches because nothing is wrong.
What follows: the lab verifies capability, never installation
The install path may differ. The verification does not.
Before the lab will raise anything, it asserts the outcomes it needs — not that packages are present, but that the machine can actually do the work:
| Assertion | Failing means |
|---|---|
| the daemon answers as the invoking user, not as root | a group membership that was granted but never took effect |
| a copy-on-write storage driver is offered | the userspace tooling is missing; snapshots will be full copies |
| the pool the lab will use is on that driver | a pool exists, and is the slow kind — the failure that has no symptom |
| hardware virtualisation is present | machines will be emulated and unusably slow |
| an image can be fetched or is cached | the first raise will fail late instead of early |
Each check states why it matters, in the terms of what it costs. "The pool uses the dir
driver" means nothing to someone who does not already know it means seventy-six times slower
and unbounded at worst.
The lab refuses to run degraded. It does not warn and continue: a warning about a slow inner loop is read once and ignored forever, and the loop stays slow. This is ADR 0008 applied where the failure is performance rather than an error.
Two ways the prerequisites arrive
On a machine the mesh manages — a module declares them, and a hook turns them into capabilities: the units enabled, the group granted, the pool created on the right driver. This already works; it is what was done for the virtualisation daemon itself.
On a machine the mesh does not manage — the lab's own bootstrap does it. One command, on a clean machine, that installs what is missing and configures it.
The second path is not a convenience. It is required, because the lab must work before the mesh does, and a lab that could only be installed by a mesh would be unable to host the development of the mesh that installs it.
Both paths end at the same verification. Whoever satisfied the prerequisites, the lab checks them itself — because the lesson of the first failure is precisely that something else said it was done is not evidence.
The lab is the second thing installed by hand
Worth stating, because it looks like an exception and is not.
The node host is the one thing installed by hand on a machine (research 006): everything else arrives through it. The lab is the same shape on a workstation — installed once, by hand, and then everything about the mesh is developed inside it.
Two bootstraps, at two levels, for the same reason: something has to be first, and pretending otherwise produces a circularity that gets papered over with a script nobody exercises.
What a clean install actually needs
In order, on a machine with nothing:
- A virtualisation daemon, running, with its socket enabled.
- Copy-on-write storage tooling — the kernel side is usually already present; it is the userspace half that is missing and that decides whether the driver is offered at all.
- A pool on that driver. A loop-backed file is sufficient and needs no partitioning, which matters: requiring a dedicated filesystem would make the lab uninstallable on a machine already in use.
- Group membership for the operator — which does not apply to sessions that already existed. Observed directly: a shell whose process tree predated the grant could not reach the daemon while a fresh lookup showed the membership present. The bootstrap has to say so, or the first thing a person meets is a permission error that looks like a broken install.
- Verification, as above, before anything is raised.
Open
- Whether the lab's bootstrap may install packages at all, given that the mesh's rules forbid installing by hand. The resolution is probably that the lab's bootstrap is the sanctioned mechanism on an unmanaged machine, in the way the mesh's own first-node script is — but that is an argument to record, not to assume.
- What "adequate" means numerically. The checks above are qualitative. A snapshot-time threshold would catch a copy-on-write pool that is slow for some other reason, and would be a real assertion rather than a proxy.
- Whether the lab should own its pool rather than using an existing one. Owning it makes the driver guaranteed; sharing it avoids duplicating storage on a machine that already has a pool.