Pinning the connection to the old server returned a catch-all certificate and a 404

The migration checklist had an item that read “rollback runbook exercised once for real”, and it sat unticked because nobody had ever run the rollback.

Two rollbacks, one of them proven

We were moving customer web addresses from our old server onto a CDN in phases. The plan promised that if a migrated domain misbehaved, we could point its DNS back at the old server and it would carry on. Nobody had walked that path.

When we sat down to close the item, the first job was working out what had actually been tested. Recovering the relay in the middle had been run. Flipping a domain back to the old server had not. It existed as a paragraph.

Finding a domain that could be rolled back

The rollback only works if the old server still holds that domain’s own certificate. Without it, the old server answers a browser with a generic catch-all certificate and a 404, or with no handshake at all.

We went in believing three of our test domains were in the right state. They were not. The old server held zero bindings and zero certificates for any of them, because an earlier cleanup had already run. Believing that from memory cost us several turns before we checked. A fourth had drifted to a different host entirely.

The domains that qualified were a cohort of four expired test domains that we manage ourselves. Each still held four bindings and two certificates on the old server. We picked one that was half migrated, with the www name already on the CDN and the bare name still on the old server. The old certificates were valid until mid July.

The drill: four steps, real DNS edits

• A, finish the migration. The bare name moved to the relay with a 600 second TTL. Live check: it redirected with a 301 to www.
• B, prove the way back still exists before touching anything. Pinning the connection straight to the old server with curl -sk --resolve www.<domain>:443:<old-server> https://www.<domain>/ returned a 2xx or 3xx with a valid certificate for both names.
• C, roll back. The bare name pointed at the old server again. The www name was a CNAME to the CDN, and the registrar will not change a record’s type inline, so we deleted the CNAME and added an A record. The registrar’s own name server and the public resolver both returned the old server for both names. The old server kept serving HTTPS on the retained certificates.
• D, restore exactly as found. The A record went back to a CNAME. www was back on the CDN’s certificate, and the bare name was on the old server. Net change to the domain: zero.

The contrast made the case. Run the same step B check against a domain whose cleanup had already run and you get the catch-all certificate and a 404. Swept means no way back. Retained means an instant way back.

What we wrote down

The runbook’s first step is the non-destructive one. Run the pinned request, and if the answer is the catch-all certificate, a 404 or no handshake, stop, because the certificate was swept and rollback is unavailable. We also filed a ticket for a settle window on the cleanup, since the thing that makes the rollback work is the thing cleanup deletes.

The status word that stood us down

Partway through the drill the agent read chrome-bind: disabled ... hold-the-line and concluded there was no browser available. That flag only stops session tabs auto-binding to the slot pool. The browser tool itself worked and could be driven directly. We renamed the status to autobind-off and reworded the reason to say what it switches off. The note we left in the session was to list the open pages before standing down on any label that says disabled.

The session ran 2h 49m. The bare test domain is back as it was, and the runbook has a one-command check for whether a domain can be rolled back. Every domain the cleanup has already swept is a domain where that check would say stop.

Run it once before you depend on it

A rollback plan that nobody has run is a promise, not a safeguard. Before a migration depends on one, run it once on a domain you can afford to touch, starting with the non-destructive check that the old server still holds the domain’s certificate. Any cleanup that deletes those certificates removes the way back.

dxdev LESSON · paste into your AI coding agent
LESSON: A Rollback Plan Is a Claim Until You Have Run It, and Its Precondition Is the Thing Cleanup Deletes
SOURCE: dxdev.com/blog/rollback-plan-nobody-had-run
WHAT HAPPENED: A phased migration of customer domains to a new edge had a gate item that read "rollback runbook exercised once for real". Two rollbacks had been described, and only one of them, recovering the relay, had ever been run. The domain rollback, pointing a migrated domain back at the old server, was still a paragraph. To run it I needed a domain that was migrated but whose old certificate still existed on the old server. Three of my own test domains looked like candidates from memory, but the old server held no bindings and no certificates for any of them because a cleanup had already run. I used one of four expired managed test domains that had kept everything, moved it forward, rolled it back with real DNS edits, and restored it to exactly how I found it. It kept serving HTTPS from the old server the whole time because the old certificate was still there. Mid-drill a status reading "disabled" made the agent conclude it had no browser and stand down, when the flag only turned off tab auto-binding.
THE RULE: Run a rollback once before you rely on it, on a subject you have checked qualifies. Find what the rollback depends on (here, a certificate the old server still holds), then make the cleanup that removes it wait. Name statuses for what they turn off, because an agent reads them as instructions.
CHECK MY CODE, then report PASS or FAIL with file:line for each:
  1. Any documented rollback or restore procedure that has never been executed end to end, with a recorded before and after.
  2. Any cleanup or sweep step that deletes something a rollback path depends on, with no settle window.
  3. Any status or flag name that an agent could read as "capability unavailable" when it only means "one feature is off".
THEN PRINT: a table (check, PASS/FAIL, evidence, fix) + a verdict (applies / partially / OUT_OF_SCOPE / no) + the single most important next action.