At some point in time most Information Technology (IT) departments have had to migrate an application or service from one platform to another, in this case I mean a different operating system as the platform. This is most often driven by a cost savings that can be obtained on the new platform, either through lower hardware maintenance costs, or lower support costs for the software on this new platform. The challenge with these migrations is that often times, the application is stable on the existing platform, and any migration introduces the risk of introducing instability.
The points of review documented below are not specific to any operating system (OS) on the market, but rather are a guide for migrating from any single OS to a different OS. Currently the IT world is seeing the largest percentage of these types of application migrations from UNIX-based platforms to a Linux based platform. But, just because this is occurring now does not mean this will always be the most common migration path, in time a new OS could come on the market providing advantages not currently available.
Many modern programming languages are portable in the sense that they can very easily be migrated from one host OS to another. This is not true for some legacy programming languages; this framework is meat to cover both these cases. Even with modern programming languages, some underlying libraries can vary from OS to OS and will require detailed migration planning.
Below is a framework for the process for reviewing the application being migrated and developing a plan for the migration. This framework is structured to ensure that the same steps can be used, regardless of the original and future OS.
Application Source Code
When initially reviewing an application to migrate from one OS platform to another, the source code must be checked from a process, availability and legal standpoint. This is the first phase to determine if the application can even be migrated to a new platform.
Is the source code available?
This is often an overlooked component of legacy applications. Often times the source code is not available either because it was lost, or because the intellectual property for the application has been transferred to another party. This is an important part of porting an application, and can cause alternate applications to be looked at or developing the application from scratch.
As part of reviewing the availability of the source code, it is also important to review legal obligations around that source code. Specifically open source applications often have requirements for submitting changes to the community, depending on the usage model of the application. These legal obligations are also important regarding trademarks, copyrights, and their implications on staff that previously worked on the application being reviewed.
Review of Application Source Code
After determining if the application source code is available, and determining what changes can be made and how to communicate that to external parties that may be required, it is time to review the source code technically to develop a plan for the migration and porting activities later.
Looking at what language the application is developed in is a first critical step. This will enable the planning team to determine if the company has the necessary skills to port the application, or if external resources will be needed for the migration. Knowing the language can also assist with planing supportability on the new OS based on how the well the language is supported and used in the community.
As part of reviewing the source code, a review of the libraries used should be done. This review should be done to ensure that the libraries will properly work on the new OS, that they are still available, and that they are compatible with other libraries that will need to be installed. This is the time to ensure no dependency problems are found later in the migration.
The source code review should also include an assessment of what calls and functions are now deprecated; this can include external libraries, kernel functions and other external resources. Any section of the application code that references deprecated functions should be reviewed to determine the best supportable path forward to ensure that functionality is not compromised.
Define Testing and Roll out Strategy
Now that the source code has been reviewed, it is time to define success for the migration. This component of the process is to ensure that relevant metrics are clearly defined for the time period of the migration, and after the migration so that staff using the application are not negatively impacted by the migration.
Defining data integrity standards should be the first metric for all migrations from OS to OS. This is critical to ensure that data is consistent both during the migration, and handled in the proper way after the migration. A migration of an application from one OS to another should not ever require the compromise of data integrity standards.
Second to data integrity is functionality. Staff become used to the tools they use on daily basis, and any change in the capability or functionality of those tools can cause a significant drop in performance. All migrations should include reviews to ensure that all utilized features will continue to be available for staff to utilize.
Performance is an important metric to define prior to migrating an application from one OS to another. Performance can change dramatically between OS platforms and should be planned for both testing and proper application tuning during the migration process. Performance can include many metrics including response time, reporting generation time and response time under heavy loads.
While one OS is not necessarily more or less secure then another, each have their own methods for setting permissions, logging system activity and patching against known vulnerabilities. The migration plan should include a proper review of these differences to ensure that staff are properly trained to handle securing the application once it is running on the new OS.
Stability is commonly defined as uptime or availability of an application. Introducing a new OS to an environment can change the availability characteristics, either because of new, unfamiliar processes, or because of a misplaced expectation about an OS's capability. A plan should be developed to define what availability is required of the application, and documentation on monitoring those metrics.
Porting of Code
After defining the above metrics, we can begin the longest portion of any application migration. The actual porting and testing of the application to the new OS platform. This phase will include both making modifications to the code base to ensure it works on the new OS platform, as well as testing the application on the new OS platform to ensure it properly meets the metrics defined above for success.
Maintenance Cycle Definition
During the porting of the application data can be gathered about necessary maintenance that will need to be done regularly on the new platform. This maintenance cycle will need to include time to update patches to both the underlying OS, as well as do maintenance on the data supporting the application. This maintenance cycle should be defined prior to roll out so that staff can be properly trained on this maintenance cycle and end users can be prepared for a possible change in availability policies for the application.
Update DR Processes and Tools
Disaster Recovery (DR) is an important component of all application migrations, ensuring that a properly plan is in place to recover from catastrophic failures and ensure the data and application are available for use. As part of the application migration, the DR processes should be reviewed to adequately reflect the changes in how the application is hosted and what precautions should be taken for backup, replication and training for recovery.
Training is a two part activity, both the administrators for the application as well as the end users will need to be trained on the changes in administering and using the application. Training should be provided to the appropriate staff prior to migrating the application, this will ensure that staff are ready for all change that come as part of the migration. Training should additionally be made available for staff to reference back after the migration to answer questions that could come up about the migration.
Application Roll out
After the above metrics for success are defined, the code is ported and tested and staff are trained, the application migration can be completed. This migration will include the migration of any necessary data for the application, as well as the application delivery infrastructure. This migration can be done is phases if the architecture of the application will support it, or may require an extended outage to properly migrate and test all components.
Migrating an application from one hosting OS to another is a common practice, yet, very often it is done with very little planning. As IT continues to evolve, it is inevitable that new OSs with innovative features will become available, necessitating the need to migration applications between them. Keeping a solid process that is followed each and every time will ensure stability in the migration, integrity of the data and maintaining productivity of the end users.