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Application Tier Considerations for Moving to the Cloud or x86

Before moving a single-tier application to a multitier architecture, it’s important to examine workload activity and business requirements.

Blue and green arrows in different directions.

With more enterprises moving to the cloud or x86, traditional IBM z/OS® applications are being examined for deployment on the cloud or x86-based servers. z/OS applications are mostly single-tier, while applications on other platforms are multitier. A fundamental difference exists between single- and multitier application architectures and their placement on cloud and x86 requires important considerations.

Single-Tier Applications 

So, what’s a single-tier application? Most applications have a programming component and a data component—meaning programs will use data, which could be in the form of a simple sequential file, through a complex database. The programs run and use data, which must be in-memory with the application. On z/OS, all resources are shared and thus many processes run concurrently. This allows for programs to run and for data to reside, and be accessed on the same physical box. If the application component and the data component run together within the same OS image, it can be considered to be single-tier.

Multitier Applications

On x86 and other distributed platforms, the program and the data are typically run on different OS images. This is achieved by running application servers and database servers, resulting in a two- or multitier application. Separating the two components creates a requirement for the tiers to communicate through a
network connection. 

Response Time, Unique File Structure and More

Network connections add latency to the response time and throughput of running workloads, which can be as much as 40% for a single application flow. This also adds a requirement to run additional network instructions, which isn’t required with a single-tier application. This requirement is applicable to both the application servers and database servers. 

Additionally, unique file structures exist on z/OS that aren’t supported on other platforms that could make conversion and migration difficult—possibly requiring application modification and re-engineering. Some examples of this are VSAM and PDS/E files that don’t have counterparts on any other platform. There are also system exits used for auditing and accounting purposes that don’t exist, along with many unique program products that are leveraged within the actual applications. 

Make an Informed Decision

Networking, latency implications and z/OS unique attributes must be taken into consideration when evaluating z/OS applications as potential candidates for conversion to cloud applications. Failure to do so can create problems with scaling and meeting existing SLAs. Additional hardware and software can help, but they can add to the total cost of operations and don’t necessarily guarantee the same SLA results. Before moving a single-tier application to a multitier architecture, it’s important to examine workload activity and business requirements. 

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