It is not an easy task to provide exact hardware requirements without first knowing the complexity of the app, workflows, forms, etc. running on the Joget Workflow platform. However, we can propose an initial architecture for you to deploy, and you can scale accordingly as the traffic grows. Additionally, scaling can be done in many ways, e.g., application clustering, upgrade of hardwarespecs, add additional hardware servers, etc.
To handle up to 500 concurrent users, for a start you can go with the following server setups:
1x Web Server (acting as load balancer) - Quad Core Intel Xeon - 2CPU - 4GB SDRAM ECC Memory - Integrated Dual Ultra2 Wide SCSI-3 Controller- At least 300GB SAS HDD - Fast Ethernet NIC PCI 10/100- IDE DVD-ROM Drive(Alternatively, you can implement a hardware Load Balancer.)
2x Application Server- Quad Core Intel Xeon - 2CPU- 8GB SDRAM ECC Memory - Integrated Dual Ultra2 Wide SCSI-3 Controller- At least 500GB SAS HDD - Fast Ethernet NIC PCI 10/100- IDE DVD-ROM Drive
1x Database Server - Quad Core Intel Xeon - 2CPU- 8GB SDRAM ECC Memory - Integrated Dual Ultra2 Wide SCSI-3 Controller - At least 1TB SAS HDD - Fast Ethernet NIC PCI 10/100 - IDE DVD-ROM Drive
Note: As for the hard disk space, it will depend on what data is stored, e.g., pdf document uploads, images, zip files, etc. In addition, you can also configure on a VM Environment if you wish.
Also, please note that you will need to use the Joget Workflow Large Enterprise Edition (LEE) in order for you to be able to setup the clustered environment.