Common Causes of Website Downtime
Most outages are caused by a handful of issues: DNS errors, hosting problems, failed deployments, expired certificates, traffic spikes, or third‑party failures. This guide explains the most common causes and how to reduce risk.
Short answer
The top causes are DNS mistakes, server failures, SSL expiration, bad deployments, and traffic spikes. Monitoring helps you catch these quickly.
The most common causes
DNS failures
DNS errors (NXDOMAIN, SERVFAIL, misconfigured records) can make an otherwise healthy server unreachable.
Hosting outages
Hardware failures, network issues, or provider incidents can take a server offline even if your app is healthy.
Expired SSL/TLS certificates
If certificates expire or are misconfigured, browsers block access and users see the site as down.
Bad deployments
A new release can introduce breaking changes, database errors, or misconfigurations that crash the app.
Traffic spikes or DDoS
Sudden surges can overload servers, causing 5xx errors or timeouts.
Third‑party dependencies
Payments, email, authentication, or CDN outages can break key flows even when your server is running.
How these failures show up
500 errors and timeouts
Server crashes and resource exhaustion often show up as 5xx errors or timeouts. These are classic downtime signals.
DNS errors
Users see “site can’t be reached†if DNS doesn’t resolve or if resolvers return NXDOMAIN or SERVFAIL.
SSL/TLS failures
Expired or invalid certificates block access and cause browsers to show warnings instead of loading the site.
Partial outages
Checkout, login, or API endpoints fail while the homepage still loads. This is common when third‑party services fail.
How to reduce downtime risk
Monitor DNS and SSL
Track DNS health and certificate expiry to prevent avoidable outages.
Use staged deploys
Roll out changes gradually and keep rollback paths ready.
Monitor critical endpoints
Don’t just check the homepage — monitor login, checkout, or booking.
Set multi‑check alerts
Confirm outages with multiple checks or locations before alerting.
Want to catch these issues early?
Start a 30-day free trial and get alerted the moment your site goes down.
FAQ
What’s the most common cause of downtime?
It varies, but DNS errors, server crashes, and bad deployments are among the top causes.
Do SSL errors count as downtime?
Yes. Users cannot access the site when certificates are invalid or expired.
Can third‑party outages bring down my site?
Yes. If payments, auth, or CDN services fail, key user actions can break even if your server is running.
What’s the fastest way to detect downtime?
Frequent checks with multi‑location confirmation reduce detection time and false positives.
Sources
RFC 7231: 5xx errors indicate server failures; 500 and 503 definitions.
DNS failure modes (SERVFAIL, NXDOMAIN) and resolver behavior.
Cloudflare guidance on SSL/TLS errors and common causes.
OWASP/DevOps best practices for safe deployments and rollback.