On September 12, 2025, Cloudflare’s dashboard and many of its APIs went dark for over an hour. The cause? Not a cyberattack or server crash, but a single line of React code that looked harmless at first glance.
At Maples Design, we see this as more than a cautionary tale. Because in today’s full-stack world, your frontend decisions directly shape your backend resilience. And when you’re building digital products that matter, even small oversights can ripple into major outages.
Let’s unpack what went wrong, why it matters to your business, and how your team can avoid the same fate.
What Happened? Cloudflare’s Unexpected Outage
At 16:32 UTC, Cloudflare deployed a dashboard update containing a subtle bug in a React component. The issue centered on a useEffect hook that repeatedly called the /organizations endpoint, part of its core Tenant Service API.
Just 85 minutes later, an update to the underlying Tenant Service coincided with this bug. The result? A flood of redundant API requests overwhelmed the service, triggering widespread 5xx errors across dashboards and APIs.
After rolling back the buggy update, an attempted fix unfortunately made things worse. Cloudflare forced all users to re-authenticate, creating a Thundering Herd effect. Millions of clients hit the login endpoint in a short period of time, causing a second wave of instability. The outage lasted until 19:12 UTC.
Why It Happened: The useEffect Misstep
The root cause was a common React issue, unstable dependencies in a useEffect hook. Here’s a simplified version of the problematic code:
const Dashboard = () => {
const [ data, setData ] = useState( null );
const params = { id: 123 };
useEffect( () => {
let aborted = false;
fetch( '/api/tenant' )
.then( res => res.json() )
.then( j => {
if ( !aborted ) setData( j );
} )
.catch( () => {} );
return () => { aborted = true; };
}, [ params ] );
return <div>{/* render dashboard */}</div>;
};Looks safe, right? But here’s the catch: params is re-created on every render. Even though its contents never change, useEffect treats it as a new object each time because objects are compared by reference, not value.
React’s dependency array uses shallow equality. So every render means a “new” dependency, resulting in the useEffect running again and making a new API call.
Multiply that by millions of active sessions, and you’ve got an internal DDoS attack.
The Real Business Impact
You might not run infrastructure at Cloudflare’s scale, but your users still expect reliability. A similar bug in your SaaS product, e-commerce dashboard, or admin panel could:
- Degrade performance during peak traffic
- Trigger unexpected costs from API overuse
- Erode user trust during critical workflows
- Complicate incident response during outages
More importantly, this incident shows how tightly frontend and backend systems are coupled today. A UI decision isn’t just about looking good, it’s part of your system’s resilience.
At Maples Design, we approach every project with this full-stack mindset: design and engineering working together to build not just beautiful interfaces, but robust, scalable experiences.
How to Prevent Similar Failures
You don’t need to slow down to build safely. You just need smarter habits:
1. Avoid inline objects in dependency arrays
Pass primitives instead:
const id = 123;
useEffect( () => { /* ... */ }, [ id ] );2. Enable react-hooks/exhaustive-deps in ESLint
This rule catches unstable dependencies before they ship.
3. Prefer stable references
Use useMemo or lift values outside the component when you must pass objects.
4. Think in systems, not silos
Frontend engineers should understand downstream impact. Backend teams should monitor client-side traffic patterns.
5. Deploy with defense in depth
Roll out changes incrementally, add observability to distinguish retries from new requests, and implement client-side backoff and caching. Small changes, multiplied across your stack, create outsized resilience.
Small Details, Big Impact
Cloudflare’s outage was a small mistake in a widely used hook, one that many developers have written before. But in today’s increasingly interconnected applications, the line between frontend and infrastructure is fading. Every line of UI code can have a large impact.
By writing intentional React logic, fostering collaboration between design and engineering, and planning for failure, you can prevent massive failures before they begin.
Because in software at scale, the smallest details can carry the heaviest weight.
And your business is counting on you to get them right.