605c9fd4415e215262324bc5dc85d43f3deb7b37
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Commits
| Author | SHA1 | Message | Date | |
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 jschoubben
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605c9fd441 |
Changes are pushed, not polled; and a stuck host rolls itself back
Two corrections and one new decision, all from Jochen catching things. Pushed, not polled. I described updates as landing "on the next reconcile", which reads as polling and is not the design. A declaration arrives as a message on a link that is already open; the host applies it then. Polling over an existing connection would be slower to land AND constant traffic to learn nothing. The timer is for drift and nothing else, and it cannot be replaced by an event for a definitional reason: drift is change the mesh did not make -- somebody edited a managed file, a distribution upgrade replaced a config -- so nothing will ever publish a message about it. Only looking finds it. Separated the heartbeat from the reconcile timer, which I had been conflating. They point in opposite directions and answer different questions: the timer looks at the machine and asks whether it still matches; the heartbeat reports upward and is what makes silence mean something. A node with nothing to do sends nothing, and without a heartbeat that is indistinguishable from a node that stopped. 0059 -- a host that cannot start is rolled back by the service manager. I had left this open on the grounds that recovery meant the host judging its own health. That objection does not survive being asked properly: a keepalive is something else judging the host. The watchdog must be local, because nothing dials a node and a host that cannot start cannot report -- so it is the service manager, which is already there. The failure it prevents is sharper than "the node is down": a host that will not start looks exactly like a machine somebody switched off, which is the one condition this design has deliberately decided not to alarm on. So a bad release reaches every node, each goes quiet, and the mesh reports a fleet of sleeping laptops. Confirmed means started and completed one reconcile -- deliberately not "the link is up", or a laptop on a train would roll itself back. The rollback is a script shipped by the package, not a host subcommand, because a binary that will not start cannot be its own recovery. It rolls back once: a second failure means the machine is the problem, not the binary. Also refined the records checker, which produced a false positive: a proposed record may extend another proposed one, because decisions are drafted in chains and the alternative is marking things accepted to satisfy a check. An accepted document resting on a proposed record still fails, and that was verified. 0057, 0058 and 0059 are all proposed. |
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jschoubben
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aeea2a9f9a |
Resolve the host lifecycle's open items, and say how the host is delivered
The upgrade question turned out to be a delivery question, so 0058 answers both. Today's third silo runs once per node and sends each one a command to install and start. That is where the as-is records a package install that 404ed from every mirror while the job went green, an image pull failure that did not fail the deploy, and a verify stage that was built and never scheduled because it was missing from a list. The shape underneath all of those is that the thing reporting success was not the thing doing the work. Meanwhile ADR 0037 has given every node a component that applies state, reads back and reports -- so two mechanisms now change a node and only one checks its work. 0058: a pipeline ends when the declaration is updated. Deploy stops sending commands to nodes and becomes one write. The host applies it on its next reconcile, and the host cannot report success it did not verify. The verify stage disappears as a stage, which is the point -- verification stops being a step that can be left off a list. A pipeline result now means "the declaration is updated, and here is which nodes have applied it". It does not wait for every node, because a node may be legitimately switched off for a week. Outstanding is reported separately from failed, since conflating them is how the old system produced a stall with no error anywhere. The host is delivered by exactly this path and needs no new resource type: a `file` writes the package manager's config pointing at the mesh's repository, a `package` names the version. Added a step I had missed -- before exiting for a restart, the host runs the new binary once. A package can install something that does not execute here, and that turns "the node never came back" into "the apply failed and said why". Six open items resolved: re-enrolment is decided when the token is issued and revokes the previous identity; the mesh keeps a recovery copy of what each node reports it owns, which un-strands the orphans; last-contact is reported with no threshold, because a laptop off for three weeks is doing nothing wrong; adoption always completes but a failed line makes a node ineligible for assignment; a briefing is a structured document whose outcome is computed from its lines; and the token is printed once and carried by hand, which is the property that makes it worth anything. Still open and named: automatic rollback of a host version that will not start. 0057 and 0058 are both proposed. |
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jschoubben
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2204b01909 |
Design the node lifecycle end to end
The host was described as a component and never as something that runs for years on a machine somebody else also uses. 09 covers every state a machine can be in and every transition between them. Four states: unmanaged, hosted, enrolled, disconnected. Only the last two are nodes, and they are the same node in two situations. `hosted` -- the host installed but never told which mesh it belongs to -- had no name before and is where a machine sits between the two adoption commands. Things that were unclear and now are not: The first node walks the same path in an unusual order: reconcile from the bundle, the control plane it just raised issues a token, enrol against it. Its specialness lasts two commands. A side effect worth having -- enrolment is exercised on node one, rather than being written and first used on node two. Enrolment reports profile and inventory BEFORE the control plane decides anything. The profile is the input to that decision, not a diagnostic; the control plane cannot decide what a machine should run without knowing what it can run. Rebooting mid-apply is safe by construction. The store records each resource after it worked, so a host that dies half way through comes back and applies the rest. The rule that stops the host lying about what it did also makes it crash-safe. Retiring splits in two. Graceful is a final empty declaration. A node that is gone will reconcile its last declaration forever -- the honest consequence of making disconnection ordinary. The answer is not to make the host expire but that the node holds nothing that outlives revocation: every grant is a per-node credential revoked at the provider. A lost node keeps running and stops being able to reach anything. Said plainly rather than implying the mesh can switch a machine off, which it cannot and should not. Losing the store is quiet and permanent, so it gets its own section. The host re-enrols and re-applies fine; what does not come back is removal, because resources it no longer has a record of become unowned and sit there indefinitely. Also corrects 0057, which said the mesh must not upgrade the host at all. That conflated two acts. Replacing the binary is safe -- Unix keeps the running inode. Stopping the unit is not. So the host may apply a package naming itself, and restarts by finishing its apply and exiting cleanly, letting the supervisor start it on the new binary. It never asks the service manager to restart it. That makes a fleet-wide host upgrade an ordinary declaration, which the first draft gave up on. 0057 remains proposed. |