Out of curiosity, why would you need HA for web servers. Can you just set them up behind a load balancer? Instead of having an extra web server sitting out there waiting, it will actively participate at all times, and pick up the load if one goes down.
If you could deploy ha without loadbalancer isn't that great?
How about just deploy another AWS, then you have another Web server to serve login with full AWS function (no matter the primary AWS is up/down). Value for money!
[compare to AWS HA,(if we have it), we just wait for the primary AWS to fail, letting AWS HA sitting there do nothing, but busy doing synchronization only. ]