I’d love to read more about these projects. In particular, were they rewrites, or “rehosting”? What domain and what was the avg transaction count? Real-time or batch?
Citrix is almost always used to re-host existing applications. I've only ever seen very small utility apps that were purpose designed for Citrix and always as a part of a larger solution that mostly revolved around existing applications.
Note that Citrix or any similar Windows "terminal services" or "virtual desktop" product fills the same niche as ordinary web applications, except that Win32 GUI apps are supported instead of requiring a rewrite to HTML. The entire point is that existing apps can be hosted with the same kind of properties as a web app, minus the rewrite.
I watched two such mainframe to “modern” architecture transitions recently, one at a telco and one at a medical insurance company. Both replaced what were billing and ERP systems. Both used Java on Linux virtual machines using an n-tier service oriented architecture. Both had a mix of batch and interactive modules.
Both suffered from the same issue, which is actually very common but nobody seems to know: power efficiency throttling of CPU speeds.
The irony was that the new compute platform had such a huge capacity compared to the old mainframe (20x or more) that the CPUs were only about 1% utilised. The default setting on all such servers is to turn cores off or put them into low-power modes as slow as 400 MHz. This murders performance and especially slows down the network because of the added latency of cores having to wake up from deep sleep when a packet arrives.
It was one of those situations where running a busy-loop script on each server would speed up the application because it keeps everything “awake”.
The telco doubled their capacity as an attempt to fix the issues but this took them to 0.5% utilisation and things got worse.
The health insurer also overcomplicated their network, building a ~100 server cluster as if it was the public cloud. They had nested VLANs, address translation, software defined networking, firewalls between everything, etc… Latency was predictably atrocious and the whole thing ran like it was in slow motion. They too had the CPU throttling issue until I told them about it but the network was so bad it didn’t fix the overall issue.
