What kind of heavy traffic? How many pageviews?
What are the resources on the server?
Why not use nginx? it's faster than apache and acts like a proxy and can be configured as a load balancer
https://www.digitalocean.com/community/tutorials/how-to-set-up-nginx-load-balancing
will do exactly what you want. You might also want to load static content from the cloud (Amazon, cloudflare, google docs, dropbox).
Hope it helps