Backend down: server unreachable

Also searched as: api offline · server unreachable

Updated 11 October 2026

Short answer

Call one of your API's addresses directly and see what comes back. Nothing at all (timeout, "connection refused", "could not resolve host"): the server is off or overloaded, the DNS is wrong, or a firewall is blocking it. An error code (500, 502, 503): the server is up but the app or something it depends on, usually the database, is failing. Normal responses: the backend is fine and the problem is in the app or website calling it.

What's the problem

Your app or website says it can't connect, every API call fails, or monitoring says the API is offline.

Why it happens

  • The server or app process stopped, crashed, or ran out of memory or disk.
  • The database is down, so every request fails.
  • DNS changed or the domain expired, so the address doesn't resolve.
  • A firewall or security rule blocks traffic.
  • A failed deploy left the backend not running.
  • The hosting provider is having an outage.

How to fix it

  1. Call the API directly (in a browser or with curl) and note what happens.
  2. For no response, check the server is running, its resources, DNS and firewall rules.
  3. For errors, read the backend's logs and check the database.
  4. If a deploy just happened, roll it back.
  5. Check your provider's status page.
  6. Set up monitoring on a health-check URL so you know when it happens.

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 open your app or see crash reports from phones, so check those in your app's own dashboard.

Run your free report

Your first report is free, no card needed. Then A$50 a month, up to 10 domains. Read-only: it never changes anything.

Sources

  1. MDN Web Docs: HTTP response status codesreferenceHTTP response status codes indicate whether a specific HTTP request has been successfully completed.
  2. Cloudflare: Error 522official docsAn overloaded or offline origin web server drops incoming requests.

Related

App crashing or not loading Is the app itself crashing (an unhandled error), or can't it reach its backend? Crash reports show the first; your API's status shows the second. API not working Look at the status code and response body the API returns: 4xx means the request is wrong (login, data, limits); 5xx means the API's server failed. Server not responding Nothing answered: the server is off, overloaded, out of memory or disk, or a firewall is blocking it. Check it's running, then its resources, then the network. Database connection error Your app can't reach its database: the database is stopped, the address or password is wrong, or a firewall is blocking it. Check them in that order.
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