WiseJ 3.5 sporadically displays Offline - app.wx 503 Error

[itg-assistant]

Patrick Hecker (ORDIX AG) asked 2026-02-03 10:33:02 UTC

Hello everyone,

For some time now, we have been experiencing an issue with our WiseJ 3.5 application, which sporadically displays the message “Offline” and otherwise only a white screen. The Offline message disappears after a short time. The issue then affects the entire company and does not allow any new logins.
Current sessions continue to function without any problems.
As soon as the error occurs, it is apparent that all accesses to app.wx in new sessions return a 503 error.

The error is resolved when the IIS application pool is restarted.
This error occurs irregularly, sometimes not at all for 3 days, but on other days every 2 hours.

Unfortunately, I cannot provide a test case for this, as we do not know how to reproduce the error.

Does anyone here have any idea what could be causing this or what else we could try?

Thank you and best regards,
Patrick

[itg-assistant]

JD answered 2026-02-03 15:32:19 UTC

app.wx or any  other url are served directly by the IIS server way before wisej is even loaded. When you get the error try to load an image url for example (with cache off) it will also not load. It's either the app pool crashing or your network security blocking.

[itg-assistant]

Patrick Hecker (ORDIX AG) answered 2026-02-04 08:43:24 UTC

Static resources (JS, CSS, images) continue to load. wisej.wx is also still loading. Error 503 only occurs once app.wx is loaded.
It looks as though the app pool is crashing, but unfortunately I don’t understand why, as the application normally runs fine.

[itg-assistant]

JD answered 2026-02-04 12:54:39 UTC

Look at the event viewer for the exception. It’s most likely an exception in the application.

[itg-assistant]

Patrick Hecker (ORDIX AG) answered 2026-02-06 11:11:50 UTC

It seems as though we have found the problem after discovering that it always occurs at exactly 50 user sessions.

Apparently, a parameter was introduced in Wisej 3.5 in preparation for version 4.0, but it was not documented (at least I cannot find it in the documentation). This parameter is MaxSessionsPerClient, which first appears in 4.0, but seems to have already been implemented in 3.5. Since we access the app via a reverse proxy, the 50 sessions per client are of course quickly reached.
Unfortunately, I can't find any indication in any log that this limit has been reached; the application only reports “Offline” and a 503 error without any further description.

[itg-assistant]

Julie (ITG) answered 2026-02-06 14:47:16 UTC

This was a security enhancement added as a second-level DDOS prevention. It’s being added to the docs and we’ll change the default to 0 (unlimited). It can be changed in Default.json. When clients connect through a proxy they all have the same IP and we cannot use X-Forwarded-For since it can be forged easily.