Every website goes down eventually. The question isn't if, it's when, and how long before you find out.
Most developers find out about downtime one of two ways: a user complains, or they happen to check their own site. Neither is good. By the time you find out that way, the site has often been down for 20–40 minutes.
Here are the most common reasons websites go down, and what you can do to catch them faster.
1. Server crash or out-of-memory error
A memory leak, a traffic spike, or a runaway process can push your server to its limits. When the server runs out of memory, the OS may kill processes, including your web server. Your site drops off the internet in seconds.
This is the most common cause of sudden downtime. The only reliable fix is monitoring + alerting so you catch it before users do.
2. A bad deployment
You push new code. Something breaks, a missing environment variable, a schema migration that failed, an import error in production. The app crashes on boot.
Without monitoring, you might not notice for hours. With a 1-minute uptime check, you'll know within 60 seconds of the deployment landing.
3. Database connection failure
Your app is running, but it can't reach the database. Maybe the connection pool is exhausted, the database host restarted, or a firewall rule changed. The app returns 500 errors or times out completely.
From a monitoring perspective, this looks the same as full downtime, your URL stops returning a 200. You get alerted either way.
4. Expired SSL certificate
SSL certificates expire. When they do, browsers display a full-screen warning and most users immediately close the tab. Your site is technically "up" but completely inaccessible.
This is 100% preventable. PingVault tracks SSL expiry for all your monitored endpoints and alerts you well before the expiry date, so you have time to renew without any downtime.
5. DNS misconfiguration
Someone updated a DNS record, a domain expired, or a nameserver went down. Your domain name stops resolving, which means the site is unreachable even if the server is running perfectly.
DNS issues are particularly tricky because the impact is global but uneven, some users see the site, others don't, depending on their DNS cache. Monitoring from an external location catches this reliably.
6. Third-party service dependency
Your app depends on an external API, a payment gateway, an auth provider, a CDN. When that service has an outage, your app may fail in unexpected ways: slow responses, partial failures, or complete timeouts.
Monitor your own endpoints that depend on third-party services. If your checkout page is slow because Stripe is having issues, you want to know about it even if the problem isn't yours to fix.
7. Traffic spike you weren't ready for
A tweet goes viral. You get featured on a newsletter. Suddenly you have 10x normal traffic and your server buckles. This is a good problem to have, but it still means downtime if you're not prepared.
Uptime monitoring won't prevent this, but it will tell you immediately when your site starts returning errors under load, so you can respond (scale up, add caching, or at minimum post a status update).
How to know the moment it happens
The answer is simple: use an uptime monitor. An external service makes requests to your site on a schedule, every 30 seconds to 5 minutes. The moment your site stops responding correctly, it sends you an alert.
The key word is external. If the monitor runs on the same server as your site, it won't help when the server crashes. You need a service running independently, checking from the outside.
PingVault does this. Free plan includes 50 monitors with 5-minute checks. Pro plan gives you 1-minute checks and Slack/Discord alerts. Setup takes about 5 minutes.
The longer your site is down without you knowing, the more damage it does, to user trust, to revenue, to SEO. The fix is simple: set up monitoring now, before the next incident.