How to fix error 503 backend fetch failed – magento 2

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Error 503 backend fetch failed on Magento 2 is pretty common, as you may have seen while surfing. If you are experiencing this problem right now, then I would like to explain that it is possible for this error to occur regardless of the operating system (Windows, Mac, or Linux) that you are employing or the device that you are utilising to do your browsing, such as your smartphone (Android or iOS), tablets, iPad, or other similar devices.

error 503 backend fetch failed - magento 2

Error 503 backend fetch failed on Magento 2 may currently be fixed in a variety of ways, each of which has been demonstrated to be successful. If you pay attention to what they say and do what they say, you should be able to solve the problem on your own without the need for outside technical support from a professional.

Therefore, let’s get started on fixing it, but before we do that, I’d like to give a more in-depth explanation of what the Error 503 is and what the most prevalent reasons are for why it happens while browsing.

What is error 503 backend fetch failed – Magento 2

Magneto 2 can be described as a free eCommerce platform that helps small businesses with a digital commerce solution that is flexible and helps boost online sales. It offers several features that may make it difficult in some cases.

In fact, Error 503 Backend Fetch failed with Varnish cache error is a common error faced by many. Fortunately, our Support Team has come up with this guide to help you out of this particular problem.

How to fix error 503 backend fetch failed – magento 2 – [Full Guide with Reasons]

So that’s all what we know so far about the Error 503 backend fetch failed on WordPress issue that you might encounter while browsing. If you still facing this issue on your machine then I would like to say, contact an expert!

Reason 1: The length of cache tags is more than the value that is preset for Varnish

The error could occur because the length of the cache tags is longer than the value that Varnish uses as its default. This could happen if the company sells a significant number of products. The information provided by our Support Team indicates that the default setting for Varnish is 8192 bytes.


A catalogue that has more than 400 different items is far more likely to have at least one mistake than a smaller one. You may fix this problem by modifying the value of the http resp hdr len setting in the Varnish configuration file. These are the locations at which the configuration file can be found:

For Ubuntu:

 : /etc/default/varnish

In CentOS 6:


For CentOS 7:


After the file has been located, we can use a text editor to make changes to it. On line 101, immediately below the number that is assigned to thread pool max, we will find the value that is assigned to http resp hdr len.

Take, for example:

-p http_resp_hdr_len=8192 \

We are going to have to set it to a higher value. For a product catalogue that has more than 3000 items, for instance, a size of 70000 bytes would be appropriate.

After that, we have to adjust the value of the http resp size variable to one that is consistent with the newly determined http resp hdr len. For instance, if we raise http resp hdr len to 70000, then in this particular circumstance, we will raise http resp hdr len to 10000.

As a result, following the adjustment, it will appear to be like this:

-p http_resp_hdr_len=70000 \

-p http_resp_size=100000 \

Once we are satisfied with the modifications, we will save them and then restart Magneto so that the new settings may take effect.

Reason 2: The placement of health check.php in the Varnish configuration file is incorrect

We need to find a solution to this problem if the error occurred because the location of the health check.php file in Varnish was incorrect. In point of fact, this particular file might be located in Varnish at the default location of /pub/health check.php.


In order to fix the error, we will need to open the Varnish configuration file, which can be found at /etc/varnish/default.vcl, and identify the lines that are shown below:

.probe = {

               .url = “/pub/health_check.php”;

We will then change it the following:

.probe = {

               .url = “/health_check.php”;

After that, we will head to the ginx.conf.sample file located in the Magento 2 root folder and find the following lines:

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

Then, we have to add health_check as seen below:

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

Finally, we will save the changes and restart nginx and Varnish to allow the changes to take effect.

Reason 3: Maintenance.flag file creation by Magneto 2

The var/.maintenance file is another unnecessary factor that contributes to the Error 503. Magneto 2 creates it whenever new extensions or themes are installed, whenever maintenance is performed, whenever an upgrade is applied, and even whenever the site is reconfigured.


The best course of action is to open the file manager and either rename or delete the maintenance.flag file and reloading the website in your browser.

You can even wait for some time as the maintenance.flag file is self-destructed. So, if you would like to avoid to open the backend interface then just wait for some time and try again!


In a nutshell, the knowledgeable we have finally revealed How to fix error 503 backend fetch failed – magento 2 issue. We hope these 3 solutions help you in resolving the error while working on the magento 2 so that you can make the most of your browsing experience better and secure without any hindrance.

And guys finally I would like to say if you want to share something then you can send your comment in the comment section and don’t forget to share this full and final guide with others on social media platforms.