# Upstash: Critical incident: Fly.io Upstash Redis Service Distruption

**Summary:** A critical Fly.io Upstash Redis degradation caused intermittent hangs and elevated error rates for a subset of instances. It started at 2026-05-12 09:49 UTC and resolved at 2026-05-12 13:48 UTC, lasting 3 h 59 min. Upstash implemented a fix; its postmortem reported Redis processes stalling inside a logging syscall. _(machine-written, sol)_
- Kind: Major incident · Label: degradation (model (Jev))
- Changed: 2026-05-12 09:49 UTC · Detected: 2026-10-17 18:22 UTC
- [Source: https://stspg.io/v8n17s5pgq0y](https://stspg.io/v8n17s5pgq0y)
- [Company: Upstash](https://rewindex.com/company/upstash.md)
- Versions: before (none: first archived) → after incident\_version:171/zjy39rtm1skv@e6329811b193
- Change 1 of 1 for this incident

## What changed

**1. Added: Title**

```diff
+ Fly.io Upstash Redis Service Distruption
```

**2. Added: Impact**

```diff
+ critical
```

**3. Added: Status**

```diff
+ postmortem
```

**4. Added: Start time**

```diff
+ 2026-05-12 09:49 UTC
```

**5. Added: Resolved time**

```diff
+ 2026-05-12 13:48 UTC
```

**6. Added: Update** (investigating) · 2026-05-12 09:49 UTC

```diff
+ Some regions are experiencing connectivity issues due to an ongoing network problem. We are currently investigating
```

**7. Added: Update** (identified) · 2026-05-12 10:50 UTC

```diff
+ The issue has been identified and the fix is being implemented.
```

**8. Added: Update** (monitoring) · 2026-05-12 12:05 UTC

```diff
+ A fix has been implemented and we are monitoring the results.
```

**9. Added: Update** (resolved) · 2026-05-12 13:48 UTC

```diff
+ This incident has been resolved.
```

**10. Added: Update** (postmortem) · 2026-05-15 12:43 UTC

```diff
+ On May 12th and 13th at various times, a subset of Upstash Redis instances on [Fly.io](http://Fly.io) experienced intermittent hangs and elevated error rates. The Redis process would stall inside a logging syscall — alive but not making progress — which made the issue hard to spot from our usual telemetry. After investigating with Fly's team, we identified the root cause as a bad interaction between a recent guest kernel update on Fly's newer machines and an upstream Cloud Hypervisor bug \([cloud-hypervisor#7672](https://github.com/cloud-hypervisor/cloud-hypervisor/issues/7672)\) affecting log writes from inside the VM. We mitigated by disabling the affected logging paths, and Fly has since rolled out a hypervisor-side patch, fully resolving the issue. No data was lost. Sorry for the disruption.
```

## History of this incident

| When (UTC) | Change | Label |
| --- | --- | --- |
| 2026-05-12 09:49 UTC | Critical incident: Fly.io Upstash Redis Service Distruption (this change) | degradation |

All Upstash changes: [timeline](https://rewindex.com/company/upstash/changes.md)
_Diff excerpts are shown on normalized text: dates, counters and tokens appear as ‹date›, ‹count›, ‹tok›; noise-only edits are hidden. Rewindex shows the changed passages, not a copy of the page._


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Canonical: https://rewindex.com/change/i7fc2790361abbe · Markdown: https://rewindex.com/change/i7fc2790361abbe.md · JSON: https://rewindex.com/api/v1/changes/i7fc2790361abbe · Generated 2026-10-18T03:55:41.777Z