You may want to check into Round Robin DNS. with some caveats
Round Robin DNS is a method of applying multiple IP addresses (DNS PTR record) to one hostname (DNS A record). DNS will rotate over the PTR records whenever an A record is requested. It isn't an HA solution, but if one IP address is down, the user can re-load their web browser and a different PTR will be handed out. One thing that makes it appealing is that it's a 5 minute config in DNS to add a few IP addresses, and then just clone all the VMs you want to be in the pool (NOTE: each VM needs it's own unique IP address of course).
The caveats I've run into before are:
- If the application issues a re-direct to it's hostname be aware this causes a new IP address to be handed out to the user. Sometimes the "down" IP gets handed out. This can be trouble from the get-go when doing an HTTP > HTTPS redirect.
- SSL certificates need to be considered.
- Application session state is undeterminable
Personally, I gave up on RRDS for web applications years ago (works fine for things like LDAP) but there may be new and exciting things that have developed to handle some of the above issues.
Your use case may not require SSL or redirects so maybe it's a fit, maybe not. In my expericence the HA solutions (Open Source) require a lot of complexity, time and effort to setup. Vended solutions are easy, but require deep pockets and (often times) frustrating support experience.