As you can check on the link below:
Varnish and PageSpeed can be configured to work together. You will have to take into account some extra steps when clearing the cache for instance but they can be configured to work together.
However, Bitnami stacks are not prepared for this specific configuration and that's why we recommend to disable Pagespeed when using Varnish.
In order to activate PageSpeed you just need to ensure the lines below are uncommented in the Apache configuration file /opt/bitnami/apache2/conf/httpd.conf and restart Apache:
Once you have Pagespeed running, you'd need to configure Varnish.