How to cache for multi server environment? Memcached, Redis or other?

The combination of NGINX, Varnish Cache, Memcached, & Redis is recommended for the best WordPress CMS hosting performance on a web server for high traffic websites. The load balancer is determinant in a multi-server environment, i.e. using AWS, Kubernetes, Docker, CoreOS, Mesosphere, etc. for orchestration. The best multi-server caching solution for WordPress is a CDN, where for example CloudFlare has over 150 data center locations.