Introduction

In the second article in this series ("Develop and deploy multi-tenant Web-delivered solutions using IBM middleware, Part 2: A taxonomy of current approaches to enable multi-tenancy"), we discussed the three types of multi-tenancy enablement approaches, e.g. virtualization, mediation and sharing. This article, Part 3 of the series, focuses on the third approach and addresses how to leverage a single, shared application instance to support multiple client organizations (or tenants) simultaneously, so as to achieve the goal of cost effectiveness. It explores an architecture to develop a cost effective, secure and configurable multi-tenant application using IBM middleware. We primarily focus on three key aspects of the multi-tenant application design and implementation:

• The resource sharing mechanism to reduce the hardware, software and management cost of each tenant
• The security isolation mechanism to prevent the potential invalid access, conflict and interference among tenants
• The customization mechanism to support tenant-specific UI, access control, process and data model via configuration approaches

For a better understanding, we've designed a sample application, EasyOA, which should help to illustrate how to implement the multi-tenancy model using IBM middleware products, especially the IBM WebSphere Application Server (WAS), DB2, Tivoli Directory Server (TDS) and WebSphere Process Server (WPS).

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Resources sharing based multi-tenancy enablement approaches

As illustrated in Figure 1, there are generally two kinds of resources for sharing-based multi-tenancy enablement patterns: 1) multiple application instances, and 2) single, shared application instance. The former supports each tenant with its dedicated application instance over a shared hardware, an operating system (OS) or middleware server in a hosting environment, whereas the latter can support a lot of tenants by a single shared application instance over various hosting resources. These two patterns scale quite differently in terms of the number of tenants that they can support. Multi-instance is adopted to support several (up to dozens) of tenants, each of which may own hundreds of users with a set of servers. The single shared instance is used to support a much larger number of small tenants, usually ranging from the hundreds to thousands or even more.

The selection of resources sharing patterns depends on the specific application scenarios and the target clients' requirements. Typically, a large enterprise may prefer to pay a premium for multiple instances to prevent the potential risks associated with resource sharing. For most services targeting SMB clients with small budgets for a service subscription, to achieve economies of scale, the business model has to increase revenues by recruiting a large number of clients and reducing the average service delivery cost per client by serving these clients with a highly efficient and scalable multi-tenant infrastructure. In these cases, the multiple instances pattern is not practical as the small revenue generated from each tenant won't justify the allocation of dedicated hardware/software resources for the tenant.

Although owning the great benefit of cost effectiveness, the multi-tenancy application that this article focuses on will face many challenges especially with regards to isolation and customization.

First, we should support application-level isolation among different tenants. Although all tenants essentially share the same infrastructure and application instance, from the user experience, Quality of Service (QoS) and administration perspectives, the tenant would naturally desire to access and use the service as if there were dedicated tenants. Therefore, isolation should be carefully considered in almost all parts of architecture design, from both the non-functional and functional level, for aspects such as security, performance, availability, and administration.

Secondly, we should support tenants that customize their own service in runtime without impacting others. Traditionally, customization would involve code modifications and application re-deployment. However, such a customization pattern is impractical in a multi-tenancy-enabled service environment. As all the tenants share the same application instance, once the customization is done for a particular tenant, the services for all tenants will be affected, and possibly interrupted during the update. As the number of tenants increases, the interruptions become more frequent and lead to very serious service availability issues. Therefore, the customization for one tenant without impacting other clients during the runtime should be a key requirement of a multi-tenant application.

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Multi-tenant resources: sharing, isolation and customization mechanism of J2EE artifacts

For J2EE/SOA applications, there are many kinds of resources that are accessible, as well as runtime artifacts located in multiple tiers, e.g. user interface, business logic, process/workflow, and data model. To design a highly efficient multi-tenant application, we need to carefully manage those resources via the following two steps:

• Identify all resources types that may be shared among tenants. Prioritize them according to the estimation of the degree of cost saving it can take via some sharing mechanisms
• For each kind of sharable resource, list all its potential isolation and configurable points. Evaluate and summarize the most suitable isolation and customization approaches for different multi-tenant scenarios

Table 1 gives a brief summary about those important resources and the corresponding sharing, isolation and customization mechanisms they use. We will introduce them in detail in the following articles of this series.

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EasyOA, A sample application

EasyOA is a simple office automation application developed for small businesses. The application primarily includes a vacation application process, in which the employees may raise vacation requests and query their vacation history, while a manager approves the requests of his employees. The administrator has the privileges to view the operation logs of all users of his company.

EasyOA is a typical J2EE application that is based on the following IBM middleware:

• IBM WebSphere Application Server V6.02
• IBM WebSphere Process Server V6.02
• IBM Tivoli Directory Server V6.0
• IBM DB2 V8.2

EasyOA is designed with multi-tenancy enablement. As illustrated in Figure 2, the primary multi-tenant features supported are as follows:

• Authentication and authorization introduce how to design the organizational structure and access control (privileges) data storage/access patterns. These also enhance the standard Java Authentication and Authorization Service (JAAS) modules/processes in the multi-tenant context.
• Common J2EE Artifacts introduce how to isolate and customize the resources of user interfaces and business logic via an implicit filter-based mechanism among tenants.
• Persistent Data Model identifies and evaluates all potential multi-tenant design patterns of data storage/access from many perspectives like isolation, security, customization, and performance.
• Business Process introduce how to isolate and customize the people/roles selection of human tasks or processes among tenants in a shared process templates pattern

An overall description on the architecture and implementation of these features will be given in the fourth part of this series.

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Conclusion

The multi-tenant design pattern - using a single shared application instance to support multiple tenants simultaneously - is very important to the delivery of Web applications in terms of cost effectiveness. In this article, we looked at the overall architectural design principles and related techniques of developing a secure and configurable multi-tenant application by using IBM middleware. It's the overview of a series that will follow with articles that provide more detailed information on this topic.

Resources

Learn

• The IBM SOA Web site offers an overview of SOA and how IBM can help you get there.
  
  
• "Develop and deploy multitenant Web-delivered solutions using IBM middleware, Part 1: Challenges and architectural patterns" (developerWorks, Apr 2008) describes what multi-tenancy is and presents several technical challenges for building and deploying multi-tenant web-delivered solutions.
  
  
• "Develop and deploy multi-tenant Web-delivered solutions using IBM middleware, Part 2: A taxonomy of current approaches to enable multi-tenancy" (developerWorks, To Appear) present a taxonomy of current approaches to enable multi-tenancy in web-delivered business solution (a.k.a software-as-a-service) and compare the costs and benefits of the three approaches that we have identified.
  
  

Get products and technologies

• Download IBM product evaluation versions and get your hands on application development tools and middleware products from DB2®, Lotus®, Rational®, Tivoli®, and WebSphere®.
  
  

Discuss

• Participate in the discussion forum.
  
  
• Check out developerWorks blogs and get involved in the developerWorks community.
  
  

About the authors

Bo Gao is a Research engineer working on next generation service within IBM China Research Lab in Beijing, China. His current focus is on Massive Multi-tenancy technology in SaaS (Software as a Service) area. He has rich experiences on typical IBM SOA Software Stack.

Dr. Chang Jie Guo is a research staff member working on next generation service within IBM China Research Lab in Beijing, China. In rencent years, he focus on some key technologies in Software as a Service (SaaS) area including massive multi-tenancy, agile business process management (BPM) and Web 2.0.

Zhi Hu Wang is a Research engineer working on next generation service within IBM China Research Lab in Beijing, China. His current focus is on Massive Multi-tenancy technology in SaaS (Software as a Service) area.

Wen Hao An is a software engineer working on next generation service within IBM China Research Lab in Beijing, China. His current focus is on Massive Multi-tenancy technology in SaaS (Software as a Service) area.

Dr. Wei Sun is a research staff member working on next generation service within IBM China Research Lab in Beijing, China. In recent years, Dr. Sun has been working on Business Process Services, Software as Services and Web 2.0 related research projects.

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Table of contents

• Introduction
• Resources sharing based multi-tenancy enablement approaches
• Multi-tenant resources: sharing, isolation and customization mechanism of J2EE artifacts
• EasyOA, A sample application
• Conclusion
• Resources
• About the authors
• Comments

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