# Upstash: Fly.io Upstash Redis Service Distruption

- Impact (vendor’s label): critical
- Status: postmortem
- Started: 2026-05-12 09:49 UTC · Resolved: 2026-05-12 13:48 UTC · Duration: 4.0 h
- Updates: 5
- [Vendor status page: https://stspg.io/v8n17s5pgq0y](https://stspg.io/v8n17s5pgq0y)
- [Company: Upstash](https://rewindex.com/company/upstash.md)

## 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)_
## Timeline of updates

- **investigating** 2026-05-12 09:49 UTC: Some regions are experiencing connectivity issues due to an ongoing network problem. We are currently investigating
- **identified** 2026-05-12 10:50 UTC: The issue has been identified and the fix is being implemented.
- **monitoring** 2026-05-12 12:05 UTC: A fix has been implemented and we are monitoring the results.
- **resolved** 2026-05-12 13:48 UTC: This incident has been resolved.
- **postmortem** 2026-05-15 12:43 UTC: 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.

## Rewindex changes for this incident

- 2026-05-12 09:49 UTC: [Critical incident: Fly.io Upstash Redis Service Distruption](https://rewindex.com/change/i7fc2790361abbe.md)


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Canonical: https://rewindex.com/company/upstash/incidents/zjy39rtm1skv · Markdown: https://rewindex.com/company/upstash/incidents/zjy39rtm1skv.md · JSON: https://rewindex.com/api/v1/companies/upstash/incidents/zjy39rtm1skv · Generated 2026-10-18T09:58:58.836Z