The baseline system requirements for HAProxy are quite low. Though it very much depends on the amount and kind of traffic that your site will receive. Generally, if you are seeing issues with or are concerned about the number of concurrent connections, you'll want to look at your RAM usage. On the other hand, if you are more concerned about the number of connection per second, the the CPU is you're more likely bottleneck. I'd encourage you to spend some time doing some load testing and benchmarking to better understand your individual situation. One of the great things about using the cloud is the ease of scaling up dynamically. Start some testing on a 1GB Droplet and you can always move to a larger instance right through the control panel if needed.