How can I configure Varnish Cache with Digital Ocean load balancer

I’m running a cluster of 4 servers to host a Magento e-commerce site.

1 master server with the Magento installation and all files 2 slaves that mount the master directory and serve the files 1 database

The two slaves are in a DO load balancer.

I know varnish has some LB options but how do I use it in conjunction with Digital Oceans managed load balancers?

Thanks for then help.