December 2, 2023

Error 503 Backend Fetch Failed: Are you wondering how to fix Error 503, this occurs when the HTTP cache is unable to retrieve the requested data from the web server, and Backend Fetch Failed is displayed.

Nevertheless, we’ve listed what you may do to resolve Backend Fetch Failed Error 503 below, both as a user and as a webmaster.

Error 503 Backend Fetch Failed

Numerous factors might have prevented the retrieval of the data, including a down or unavailable server, a connection that closed before the cache server finished receiving the answer, faulty backend code or plugins, and more.

What is 503 Error

Error 503 is most typically a server-related problem that arises when there is insufficient cache memory in the browser because of a backlog of requests.

If you need a layperson’s explanation of this problem, we would say that it typically happens when you request content that is cached on a server.

It is unable to react or produces results too slowly. This issue was frequently encountered when using Magento, an open-source PHP-based e-commerce platform.

Error 503 Backend Fetch Failed: What Are The Causes?

As the name suggests, this error typically results from backend problems like faulty programming or overloaded servers at busy times.

This error can potentially affect other websites housed on the same shared server as a result of a single problematic plugin or website.

Heavy packet loss at the client side might pile up requests, which in rare instances can also result in this error.

Of course, there are occasions when the server may just be unresponsive due to maintenance, but it is only a short-term problem that doesn’t require fixing.

What Can You Do as a User / Visitor?

As a user, there isn’t much you can do because this error is caused by server-side problems. However, in order to make sure everything is working properly on your end, follow these standard troubleshooting steps:

1. Repeatedly hit F5 or the refresh button to reload the page.

2. Use a ping test to make sure there isn’t too much packet loss. If so, either use an Ethernet cable or walk closer for a stronger connection.

3. Restart your router and device.

4. Close a few of the open tabs in the browser if there are several, then try loading the website again.

5. Reset the default settings for your browser. Alternately, try switching to a whole other browser.

6. Change your DNS and reset your network settings.

If you’ve taken all possible steps from your end, the only thing you can do now is to wait. Since this error is often caused due to server overload, the site should work again as soon as the traffic settles down.

Generally, we’d recommend trying to visit the website outside of peak hours, but if you need to access the site urgently, you could contact the site administrator and notify them of the issue.

How Can a Website Owner Fix Backend Fetch Failed Error 503?

Reset your network settings and modify your DNS.

If you’ve done everything you can on your end, the only thing left to do is wait. Since server overload is a common source of this problem, the site should resume functioning as soon as the traffic levels drop.

In general, we advise trying to use the website outside of busy hours, but if you require immediate access to the site, you can contact the site administrator and let them know about the problem.

Read Also!!

1. Check Varnish Plugin

You should first establish whether the problem is with your web server or Varnish if your website uses Varnish caching. This can be accomplished by disabling Varnish and attempting to fetch without it. Here are the steps to do so:

  • Join the cPanel for your website.
  • Make sure to choose Manage Varnish > Disable Varnish under the Web Accelerator section.
  • To stop it, click Confirm Action.
  • See if your website is currently loading correctly.

If the website is operating well right now, Varnish has a problem. You can restart it once to see if it resolves the problem.

If it doesn’t, you can review the log file you can create by following the instructions below to see exactly what is wrong.

To log entries where varnish response or backend response status is 503, use the following command:

  • $ varnishlog -q ‘RespStatus == 503’ -g request

To log all entries >=500, use the following command instead:

  • varnishlog -a -w /var/log/varnish/varnish50x.log -q “RespStatus >= 500 or BerespStatus >= 500”

Read Also!!

2. Change the Cache Tag Length

In Varnish, cache tags have a default size of 8192 bytes. If you go over this limit, you can get the HTTP 503 Backend Fetch Failed error.

By raising the value of the http resp hdr len parameter in your Varnish configuration file, you can fix this problem.

On how to achieve this, there is a great post on the Adobe Commerce support website.

3. Modify Varnish and NGINX Configuration Files

The procedures are for Varnish, however, NGINX can also be used in place of it. The steps to change the configuration files are as follows:

1. Find the file in /etc/varnish/default.vcl and open it.

2. Remove /pub from the line.url = “/pub/health check.php” by writing it as follows:

  • .url = “/health check.php”

3. Try adding /pub if there isn’t one.

4. Next, navigate to the Magento 2 root folder and open the

  • conf.sample file.

5. Find the following line:

  • location ~ (index|get|static|report|404|503)\.php$ {

5. Edit it by adding health_check as such:

  • location ~ (index|get|static|report|404|503|health_check)\.php$ {

7. Save the changes and restart Varnish.

Fixes Reported by Users

A user on Stack Exchange said that this problem was being caused by another website on the server and was also affecting his site.

Therefore, if you are now hosted on a shared server, you might want to think about this.

One user claimed that the hoster’s plugin was to blame for the problem. The Backend Fetch Failed error was fixed after the problematic plugin was removed.

Another user said that their problem was caused by maintenance.flag file that Magento was producing.

By login into your cPanel, you can resolve this problem by deleting or renaming the maintenance.flag file located in the Magento root directory.

It should be noted that User-Reported Fixes typically only apply to certain instances, but they are still worth looking into.

Read Also!!


1. What is a 503 Backend Error?

The 503 Service Unavailable Error is returned from a backend server under either of the following circumstances:

  • A backend server is overloaded/busy and cannot handle any new requests or
  • The backend server is down for a temporary period due to maintenance.

2. How do I fix Error 503 Varnish Cache Server?

To resolve this issue, increase the default value of the http_resp_hdr_len parameter in your Varnish configuration file. The http resp_hdr_len parameter specifies the max header length within the total default response size of 32768 bytes.

3. What does Backend Failed Mean?

It indicates that the server is malfunctioning and not responding appropriately. The error occurs when a website’s server receives more requests than it can process at a time.

4. How do I Fix Error 503 on my Android?

Corrupted cached data – This is one of the most common triggers on Android devices when it comes to this particular error code. As it turns out, certain Android builds will trigger this particular issue if cache data folder becomes corrupted. In this case, you can resolve the issue by clearing the cache data.

5. What Causes a 503 Error?

The HyperText Transfer Protocol (HTTP) 503 Service Unavailable server error response code indicates that the server is not ready to handle the request. Common causes are a server that is down for maintenance or that is overloaded.

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