I had two VPS from another hosting company and i would like to set a droplet and configure this droplet to be a load balancer for these two external VPS
Yes. This should not present a problem. Regardless of the location of the machines behind your load balancer you would just specify them by their IP. We have a whole section of tutorials on setting up load balancing solutions. I'd recommend starting there.
alright thanks , one more thing ..
what about the IP addresses of the droplet and the external servers? it should be public or private?
When load balancing for servers outside the same DO datacenter you would use only public IPs.
For any droplets within the same datacenter you could use the private interface.
so I set the droplet IP to private and the external servers to public?
Sorry, let me clarify. If your load balancer is on a droplet and your other servers are outside DO you would only use public IPs for everything. DO private IPs only allow for communication between two droplets in the same datacenter.
alright thanks alot, am going to use the droplet as a load balancer for the external servers so there will be aren't any other configuration in this droplet
if the type of os of my external servers is centos 6.6, the type of the image for the droplet will be centos 6.7?
Since a load balancer simply routes traffic via HTTP/HTTPS it doesn't matter a lot what distro you use. If you're looking for consistency then, yes, it would make sense to go with the CentOS 6.x image we provide.