The State of AS400 iSeries Application Modernization 

 October 11, 2017

By  NickLitten

Typically our aging AS400 and Iseries applications are stateful. So, if we are looking at iSeries application modernization, is it a mistake to try and simply modernize beautify them retaining their stateful flow, or should we be looking at refactoring them in a stateless direction?

The State of AS400 iSeries Application Modernization 1

Is it really a mistake to use a stateful architecture for modernized web applications?

I think of stateful modernization as ending up with a modern looking application. It’s really just skin deep, if we screen scrape or lay a nice graphical tool over our old green screens. It’s not modernization is just making an old application look modern. (you all know the major players in this space, so I’m not going to name names and get myself in trouble 😉

I guess as an IBM RPG developer my main question is “Do I want a modernized web solution to be built around what is comfortable with existing old-school RPG programmers or designed and built focused on the businesses future needs?

What does this waffling nerd mean when he talks about AS400 Modernization – “stateless” and “stateful”?

Stateless Model

In the pure form of the stateless model, a client program makes a request to an application server, which sends data back to the client. The server treats all client connections equally and saves no information from prior requests or sessions. A website that serves up a simple static web page is a good example of the stateless model. The server receives requests for pages it hosts and sends the page data to requesting browsers, much like a short-order cook making meals for diners.

Stateful Model

When an application operates in a stateful mode, the server keeps track of who users are and what they do from one screen to the next. Preserving the state of users’ actions is fundamental to having a meaningful, continuous session. It typically begins with a login with user ID and password, establishing a beginning state to the session. As a user navigates through the site, the state may change. The server maintains the state of the user’s information throughout the session until logout.

The State of AS400 iSeries Application Modernization 2

Stateless should be the Goal

The main advantages of a stateless approach may not always be obvious. But as a web project evolves the design advantages will be come sharply obvious. Overlooking them will almost always limit us. So lets look at some of the best advantages of STATELESS design:

Industry Standard: Almost every mobile or desktop web application is stateless. A stateful application on the other hand is most common in green screen development.

Leading Edge Technology: Using standard UI technologies like jQuery and scripting is far more flexible and responsive than beautified Rich Display files or DDS to XML/JSON conversions.

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Scalable: Stateless is clearly more scalable because it runs in batch in a pool of APACHE jobs. Stateful applications require one job per user and a persistent connection which can create a bit of a log jam.

Flexible Navigation: Browsers were made for stateless web applications which do not need to be navigated linearly. Stateful applications force you to enter and exit from a certain spot.

Modularity: Stateless applications are ideal for a services oriented architecture and make our applications more modular.


Stateless is the future.

Beautifying legacy Stateful applications is just applying a bandaid.

iSeries Application Modernization -- programming with wood

PS: the blog header image has absolutely nothing to do with web-service technology, aside from the fact that it’s a very cool looking computer desk. I stumbled across this image online, and then while admiring it in closer detail I noticed that he owner had a rubber dildo paperweight on the shelf above the monitor. Which made me chuckle.


IBM i Software Developer, Digital Dad, AS400 Anarchist, RPG Modernizer, Shameless Trekkie, Belligerent Nerd, Englishman Abroad and Passionate Eater of Cheese and Biscuits. Nick Litten Dot Com is a mixture of blog posts that can be sometimes serious, frequently playful and probably down-right pointless all in the space of a day. Enjoy your stay, feel free to comment and remember: If at first you don't succeed then skydiving probably isn't a hobby you should look into.

Nick Litten

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