An overloaded server has more work than it can do, so everything slows down and some requests fail with 503 or 504 errors. CPU stuck at 100% is the usual sign. It's either more traffic than normal (real visitors or bots), or the same traffic but one thing now takes far more work: a runaway process, a slow database query, or a code change. Find what is using the CPU before paying for a bigger server.
What's the problem
The site is slow or times out, the hosting dashboard shows CPU at or near 100%, and you may get 503 or 504 errors or "resource limit reached" warnings from your host.
Why it happens
- A traffic spike: a sale, a newsletter, or a post that took off.
- Bots and scrapers hammering the site, sometimes a large share of all traffic.
- A runaway process: a stuck script, a cron job that overlaps itself, or malware mining cryptocurrency.
- A slow query that now runs on every page load.
- No caching, so every visit rebuilds every page from scratch.
- The plan is simply too small for normal traffic now.
How to fix it
- Find the busy process. Log in and run
top(pressPto sort by CPU). Note what's at the top. - Check traffic for the same period. If visits jumped, it's load. If they didn't, something got heavier.
- Block or challenge bad bots with a firewall or Cloudflare rules.
- Add caching: page caching for public pages, and a CDN for images and files.
- Fix the heavy query or process you found in step 1.
- Then, if traffic really outgrew it, upgrade the server or add more.
What Preventionlabs checks
One click runs the full report on your domain. For this problem it shows whether your site loads, how fast, and where its redirects go; uptime checked every 5 minutes, with an email when the site goes down and when it is back. With Cloudflare connected, it also shows which pages returned server errors (5xx) to visitors, and when; recent deploys and account changes, with their times. It can't log in to your server, so memory, disk and process problems show up in your host's dashboard and logs.
Run your free reportYour first report is free, no card needed. Then A$50 a month, up to 10 domains. Read-only: it never changes anything.
Sources
- procps (man7.org): top(1)manual page
The top program provides a dynamic real-time view of a running system.
- MDN Web Docs: 503 Service Unavailablereference
In overload cases, some server-side applications will reject requests with a 503 status when resource thresholds like memory, CPU, or connection pool limits are met.