Chapter 15
Migration Paths for Legacy Applications
15.1 Introduction
Systems that are required to provide highly available services typically have long life-cycles. Once deployed, they are in service easily for decades during which they go through periodic updates and upgrades of their hardware and software. Furthermore, during this time new technologies also emerge and for the system owners it becomes a challenge not just to understand these technologies but to decide whether any of them should be deployed in their existing system, and if the answer is yes then which ones.
As a result, we cannot speak about the updates in the traditional sense which would update some old hardware and/or software to a newer version of the same kind. The changes are more substantial. Some examples one may think of are: Replacing an object-oriented database with a relational one; migrating from one operating system to another; migrating from a legacy high availability (HA) middleware to the Service Availability (SA) Forum middleware. In this chapter we focus on this last case: On the migration of applications from a legacy HA middleware to the SA Forum Application Interface Specification (AIS) middleware.
We first look at the drivers for the migration, and then we continue with the review of the different aspects of system integration to define its levels with respect to the SA Forum specifications. Using this scale we set our ambition level for the migration, ...
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