Software supports High Availability Solution but that will move towards a higher variant PCBT and the cost will increase.
You will need 3 servers because one server will act as backend database server and two will be frontend application servers. Both application servers will be connected to same data server.
Both application servers can be used simultaneously and scaled up individually or act as replacement to each other if needed. The database server will have a real time mirror imaging backup.
The overall solution will have some added features and setup and linking of multiple instances.
PCBT is a custom arrangement. It has no fixed price. The price increases as per selective features added for custom need. In this case the price will increase by USD 1000 for overall linked setup of 2 licenses, not increase per license.
In certain cases when the anticipaed load is high, we also would consider to implement certain features like Downloading Encrypted Question Paper (2L) to application server to minimize load on database server.
If the reason for deploying a high availability solution is only that the event is critical but not too much in scale then features like downloading the Encrypted Question Paper to Application server as cache can be avoided.
This high availability architecture also increases system security as database server is not in any direct access of network. The database server is accessed only from the application server which is on a specific IP. So by restricting the IP access at the server settings level the transactions with data server can be restricted.
Again there are features of PCBT for higher security like IP specific login (1g) that will not allow the user to login from anywhere except specific network.