# How to test application resiliency by simulating the Cloudflare December 2025 outage

DevFeed: [How to test application resiliency by simulating the Cloudflare December 2025 outage](<https://devfeed.tech/articles/how-to-test-application-resiliency-by-simulating-the-cloudflare-december-2025-outage-11636.md>)

Original publisher: [Read original article](<https://www.gremlin.com/blog/how-to-test-application-resiliency-by-simulating-the-cloudflare-december-2025-outage>)

Author: Gavin Cahill

Published: 2025-12-19T00:00:00Z

Content type: tutorial

Language: en

Sources: [Gremlin Blog](<https://devfeed.tech/sources/gremlin-blog.md>)

Topics: [Failure Flags](<https://devfeed.tech/topics/failure-flags.md>), [Resilience](<https://devfeed.tech/topics/resilience.md>), [incident](<https://devfeed.tech/topics/incident.md>), [Chaos Engineering](<https://devfeed.tech/topics/chaos-engineering.md>), [SDKs](<https://devfeed.tech/topics/sdks.md>), [JavaScript](<https://devfeed.tech/topics/javascript.md>), [Node.js](<https://devfeed.tech/topics/node-js.md>), [Python](<https://devfeed.tech/topics/python.md>), [Kubernetes](<https://devfeed.tech/topics/kubernetes.md>), [AWS Lambda](<https://devfeed.tech/topics/aws-lambda.md>), [Azure](<https://devfeed.tech/topics/azure.md>)

Tags: [2025](<https://devfeed.tech/tags/2025.md>), [after-the-retrospective](<https://devfeed.tech/tags/after-the-retrospective.md>), [applications](<https://devfeed.tech/tags/applications.md>), [aws](<https://devfeed.tech/tags/aws.md>), [aws-lambda](<https://devfeed.tech/tags/aws-lambda.md>), [azure](<https://devfeed.tech/tags/azure.md>), [c-sharp](<https://devfeed.tech/tags/c-sharp.md>), [cloud](<https://devfeed.tech/tags/cloud.md>), [cloudflare](<https://devfeed.tech/tags/cloudflare.md>), [code](<https://devfeed.tech/tags/code.md>), [failure-flags](<https://devfeed.tech/tags/failure-flags.md>), [gremlin](<https://devfeed.tech/tags/gremlin.md>), [how-to](<https://devfeed.tech/tags/how-to.md>), [http](<https://devfeed.tech/tags/http.md>), [incident](<https://devfeed.tech/tags/incident.md>), [internet-traffic](<https://devfeed.tech/tags/internet-traffic.md>), [javascript](<https://devfeed.tech/tags/javascript.md>), [kubernetes](<https://devfeed.tech/tags/kubernetes.md>), [node-js](<https://devfeed.tech/tags/node-js.md>), [outage](<https://devfeed.tech/tags/outage.md>), [python](<https://devfeed.tech/tags/python.md>)

## AI overview

This tutorial explains how to use Gremlin Failure Flags to simulate HTTP 500 errors associated with the December 2025 Cloudflare outage. It describes application-layer fault injection, the distinction from network-layer experiments, and supported deployment environments and SDK languages.

## Source excerpt

Use Gremlin Failure Flags to safely simulate 500 error codes and test resiliency to outages, like the December 5th Cloudflare incident.