Monday, February 15, 2010

Modernizing Legacy Systems

Running into a co-worker at a company I worked at years ago, we sent into the routine of asking how things were with each other etc. When I asked him if they had finally made a move out of their old AS400 system, he replied in the negative. Now this is an old legacy system that has the effect on the company similar to swimming with a pair of 50 pound cement blocks glued to your feet. Of course, the company has made numerous attempts to modernize and move away from the legacy system in the past but they have all been unsuccessful. So we have the situation that the system is still in place and taking up a higher than necessary operation cost with the company unable to upgrade or replace it effectively.


This is actually a very familiar situation for a lot of organizations. Perhaps the legacy applications are not so large and not so old but the various mechanisms that prevent it from being sent into nothingness to rest in peace are the same. First let us look at the advantages and attractions of legacy systems:


  • Over a large span of time, they are firmly entrenched in the organizations way of going about things and are quite stable (even though they may be inefficient).

  • The legacy systems typically run mission critical applications that would disrupt the users/customers a great deal if they had to be replaced.

  • The legacy systems are familiar to large numbers of users and they know all the special ins and outs of the system well. A new system will entail re-education of the new system to users.


The disadvantages of legacy systems on the other hand are:

  • Enormous cost of ownership due to prehistoric technology and underlying systems. Large number of servers and staff are needed to keep it all going and make modifications as and when necessary.

  • Built eons ago with a specific purpose in mind which makes the system extremely inflexible and resistant to modifications. Any alterations take a large amount of resources, time and cost.

  • Typically poorly documented with only a few crusty old timers knowledgeable in the inner workings of the system which translates to difficulty in making modifications or replacing the system. Also the few who are familiar with the legacy systems resist attempts to share the knowledge and produce documentation since keeping things in the dark makes them valuable and reinforces their job security.


So how do we go about replacing the legacy systems? A few guidelines are as follows:

  • Create as much documentation as possible for the existing system. Ideally a complete set of requirement and functional spec documents should be created.

  • Perform proper risk management and mitigation strategies. Monitor risks all through the modernization for occurrences and perform mitigation as needed.

  • Strategize on the best way to perform the modernization. Perhaps a full scale replacement and recoding is required. Perhaps commercial off the shelf software will do the trick. Perhaps it can be replaced in bits and pieces?

  • Understand and educate staff that the disadvantages of clinging on to legacy systems are enormous and their co-operation in the matter will only be to their benefit.


Making fundamental changes to legacy systems is a hazardous task mainly because the inner workings of the systems and the inter-dependencies are so rarely understood. Typically, a small modification can have far reaching consequences. Therefore, it is best to approach this cautiously but not so cautiously that it never gets accomplished.

No comments:

Post a Comment

Post a Comment