Why I see X-Magento-Cache-Debug in production mode?

Question

I have Varnish configured in my server and my project is running in production mode, even though, I continue seeing the debug tag X-Magento-Cache-Debug in the header.

According to Devdocs - Varnish Final verification this header tag just show up in developer mode.

Why does it happen and how could I solve it? Thanks

Answer 1

The X-Magento-Cache-Debug header is set by Varnish VCL itself. From a standard VCL:

sub vcl_deliver {
    if (resp.http.X-Magento-Debug) {
        if (resp.http.x-varnish ~ " ") {
            set resp.http.X-Magento-Cache-Debug = "HIT";
            set resp.http.Grace = req.http.grace;
        } else {
            set resp.http.X-Magento-Cache-Debug = "MISS";
        }
    } else {
        unset resp.http.Age;
    }
    # ....
    unset resp.http.X-Magento-Debug;
    # ...
}

So its inclusion is dictated by presence of the header X-Magento-Debug which is set by Magento code here:

            if ($this->state->getMode() == AppState::MODE_DEVELOPER) {
                $result->setHeader('X-Magento-Debug', 1);
            }

As you can decipher from the code above, Magento 2 sets theX-Magento-Debug header for Varnish when it's being run in developer mode.

"For Varnish" - taking note that few lines later (in VCL), the X-Magento-Debug is being unset and clients will only see the X-Magento-Cache-Debug header.

Subsequently, make sure that you're not dealing with the note from your own post:

Environment variables may override this value

Make sure that:

• NGINX/Apache is setting production mode via an environment variable (as opposed to developer or default), e.g.: set $MAGE_MODE production; (NGINX)
• You are using the standard VCL code
• You have cleared PHP OPcache - potentially, you are running with validate_timestamps = Off, and the PHP-FPM pool is still running in developer mode until the cache is pruned.

Answer 2

I think it's normal if you're using Magento version >= 2.4.4. Because the code has changed in the varnish6.vcl.

Now the code is as the following:

sub vcl_deliver {
    if (resp.http.x-varnish ~ " ") {
        set resp.http.X-Magento-Cache-Debug = "HIT";
        set resp.http.Grace = req.http.grace;
    } else {
        set resp.http.X-Magento-Cache-Debug = "MISS";
    }

Now X-Magento-Cache-Debug header is included in all deployment modes.

For more information: https://github.com/magento/magento2/blob/2.4.4/app/code/Magento/PageCache/etc/varnish6.vcl#L210