Troubleshooting Nginx Errors: Fixing Host Not Found in Upstream Issues

When you encounter the "host not found in upstream" error in Nginx, it can be a real headache. But fear not, with a few troubleshooting steps you can get your server back up and running in no time. This quick overview will guide you through the steps to resolve this error. By checking your Nginx configuration files and DNS settings, you’ll soon find the culprit and fix the issue.

Step by Step Tutorial: Troubleshooting Host Not Found in Upstream Error

Before we dive into the steps, let’s understand what we’re trying to accomplish here. Fixing the "host not found in upstream" error involves checking our configuration files for any typos or incorrect settings, ensuring our DNS is correctly resolving, and verifying that the upstream server is running properly.

Step 1: Check Nginx Configuration Files

Inspect your Nginx configuration files for any typos or incorrect hostnames.

When you’re dealing with Nginx, configuration files are your first port of call. A simple typo can throw the whole system off. Make sure that the upstream server’s name in the configuration file matches the hostname exactly as it should be. Look for extra spaces, misspellings, or missing semicolons that could be causing the error.

Step 2: Verify DNS Settings

Ensure that your DNS settings are correctly pointing to the right IP addresses.

DNS issues are another common cause for this error. Your server might be looking for a host that simply doesn’t exist because of a DNS misconfiguration. Check that your domain name correctly resolves to the IP address of your upstream server. Use tools like dig or nslookup to verify DNS records.

Step 3: Check Upstream Server Status

Make sure that the upstream server you are trying to connect to is running and accessible.

Even if your configuration files and DNS settings are perfect, if the upstream server is down, you’ll still get the "host not found" error. Ensure that the server is running and that there’s no firewall or network issue preventing Nginx from connecting to it.

After completing these actions, you should have resolved the "host not found in upstream" error. If the issue persists, you may need to delve deeper into server logs or consider seeking assistance from a network professional.

Tips for Troubleshooting Host Not Found in Upstream Error

  • Always backup your configuration files before making changes, so you can easily revert back if necessary.
  • Pay close attention to the error logs. Nginx’s error logs often provide valuable information that can pinpoint the exact problem.
  • If you made recent changes to your DNS settings, remember that DNS propagation can take some time. You might need to wait a bit before the changes take effect.
  • Consider using a linter or syntax checker for your configuration files. These tools can catch typos or formatting errors that might be hard to spot manually.
  • Keep your Nginx and all related software up to date to prevent issues caused by outdated software or known bugs.

Frequently Asked Questions

What is Nginx?

Nginx is a high-performance web server that is also used as a reverse proxy, mail proxy, and HTTP cache.

What does "upstream" mean in Nginx?

In Nginx, "upstream" refers to the server or group of servers that Nginx is forwarding requests to.

Why does "host not found in upstream" error occur?

This error typically occurs when Nginx cannot find the hostname of the upstream server in the DNS or if there’s an issue with the configuration file.

Can this error be caused by a firewall?

Yes, if a firewall is blocking the communication between Nginx and the upstream server, you could encounter this error.

Is it necessary to restart Nginx after making configuration changes?

Yes, for changes to take effect, you need to restart or reload Nginx.


  1. Check Nginx configuration files for errors.
  2. Verify that DNS settings are correct.
  3. Ensure the upstream server is running and accessible.


Troubleshooting the "host not found in upstream" error in Nginx can be a bit of a detective game, but it’s usually not too complicated. By methodically checking your Nginx configuration files, verifying DNS settings, and ensuring the upstream host is up and running, you’re likely to solve the mystery. Remember, attention to detail is key – one wrong character in a configuration file can be all it takes to bring things to a halt.

Don’t let this error discourage you. With a calm approach and a bit of patience, you’ll have your Nginx server purring like a kitten in no time. And if all else fails, there’s always a vibrant community of Nginx users and experts out there ready to lend a hand. So, roll up your sleeves, and let’s get cracking on fixing that pesky "host not found in upstream" error once and for all!