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Transforming the Role of Legacy with Service-Oriented Architecture
Legacy comes in many forms: custom-coded applications with long-lost source code, unsupported packaged applications, or mainframe-based programs with proprietary interfaces. The paradox of legacy is that for most enterprises, these systems are too old to justify ongoing improvements, but are nevertheless too important to retire. As a result, companies often feel that they must continue to maintain their investments even though the returns they receive from these older systems may diminish over time. Actually, legacy systems wouldn’t be such a cause for consternation, if it weren’t for the fact that so much business value resides on these systems—both in the form of essential data as well as critical business logic. Migrating these complex systems is costly and time consuming, and in cases where the mainframe is mission critical to the business, is simply not an option for some organizations. After all, if it were easy to retire these systems, there wouldn’t be nearly as many of them around.
Migration, Enablement, and Rejuvenation of Legacy Systems
Many technologists have found it difficult to build or run new applications on legacy platforms, and many times older operating systems, enterprise applications, or middleware fail when made to perform new tasks they were not originally designed for. There’s no denying that in some cases, the legacy system poses significant problems that lead to reduced business value because the software no longer meets business needs or is too inflexible to change. Some organizations also find themselves in the situation where certain legacy systems duplicate existing functionality, either with other legacy or with newer systems or applications. In those cases, they will likely seek to develop a legacy migration and retirement strategy.
Extracting the value out of legacy has many facets. The adoption of Service- Oriented Architecture (SOA) can simplify the process of legacy migration, as well as legacy enablement and legacy rejuvenation. An illustration of the relationship among legacy migration, enablement, and rejuvenation within the context of SOA is shown in the figure below.
Legacy migration, while it can reduce the ongoing costs of maintenance, can also present substantial risks to the enterprise. Rarely is an older system entirely superfluous; far more often it still serves some valuable purpose at the time of its retirement. In those situations, it is essential to transition the consumption of its capabilities to a replacement system in as seamless a way as possible. More frequently, however, organizations find that they don’t actually require the retirement of legacy systems. Instead, they face issues relating to the usability of the legacy applications, or the applicability of those applications to evolving business needs.
In such cases, it makes more sense to put together a legacy enablement strategy that seeks to improve the value of the system in question without requiring its retirement. Web Services provide the flexibility to abstract mainframe functionality for immediate reuse or as a path for easier migration. For example, one migration scenario would be to wrap legacy transactions as a Web Service and in turn expose the Service via a Web interface, supporting an online application. It might also be feasible to migrate a duplicate instance of the legacy Web Service implementation to a distributed environment, enabling the eventual decommissioning of the original legacy transaction without any disruption to the business.
Such legacy enablement can clearly provide new business value, but in today’s environment of rapid change, increased competition, and limited budgets, the business is calling upon IT to squeeze even more value out of legacy technology than migration or even enablement can provide. To meet today’s IT challenges, it’s necessary to rejuvenate the legacy environment, in other words, to obtain more value out of older applications than their original programmers intended. The greatest challenge to legacy rejuvenation involves making changes to the legacy environment itself; in fact, in many cases, such invasive changes are impractical or impossible. The secret to successful legacy rejuvenation, therefore, is to employ a non-invasive approach that extracts new value out of older systems without requiring risky changes to the systems themselves.
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