Troubleshooting Magento ESI Varnish Cache Issues

If you encounter issues with the Magento ESI Varnish Cache not working properly, follow these steps to troubleshoot and resolve the problem:

Identifying the Issue

When utilizing the ESI Cache in Magento, Varnish should render the Magento ESI blocks. One common issue is the absence of the top navigation due a wrong varnish configuration for the ESI block cache.

If you notice the following code snippet in your HTML content:

<div>
  <esi:include src="http://domain.com/index.php/page_cache/block/esi/blocks"/>
</div>

It indicates a misconfiguration in your Varnish setup and shows that the ESI html tags are not rendered by varnish.

Configuring Varnish with ESI Cache

Verify Nginx Configuration: Ensure that Nginx is correctly configured to work with Varnish.
Start Varnish Daemon: Start the Varnish daemon with the necessary features enabled. Use the following command:
```
-p feature=+esi_ignore_other_elements \
-p feature=+esi_disable_xml_check \
-p feature=+esi_ignore_https \
-p http_resp_hdr_len=16k \
-p http_resp_size=64k \
-p workspace_backend=64k \
```
If using systemd, create a custom configuration file at /etc/systemd/system/varnish.service.d/customexec.conf with the specified content.

[Service]
ExecStart=
ExecStart=/usr/sbin/varnishd -j unix,user=vcache -F \
-a :80 \
-T localhost:6082 \
-f /etc/varnish/default.vcl \
-S /etc/varnish/secret \
-p feature=+esi_ignore_other_elements \
-p feature=+esi_disable_xml_check \
-p feature=+esi_ignore_https \
-p http_resp_hdr_len=16k \
-p http_resp_size=64k \
-p workspace_backend=64k \
-s malloc,256m

And reload systemd

sudo systemctl daemon-reload

Enable ESI Processing: Modify your Varnish default.vcl file (usually located at /etc/varnish/default.vcl) to include ESI processing. Add the following line within the vcl_backend_response section:
```
sub vcl_backend_response {
...
set beresp.do_esi = true;
}
```

Restart Varnish

After making these configurations, restart the Varnish service using the following command:

sudo service varnish restart

By following these steps, you can address issues related to Magento ESI Varnish Cache not functioning as expected.