Service Oriented Architecture - Big Picture

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As the old Chinese proverb goes “A picture is worth a thousand words”. Look at the picture below, I will then follow up with a few words. In the below picture components colored sky blue are old existing systems and the components in light green are new systems.

Legacy Systems and New Systems

As the above picture shows System 1, System 2, System 3 and System 4 are old systems which were developed long before SOA had become popular. System 5 and System 6 are new systems which have been developed as services.

Old systems need not be developed from the scratch but can be modified into services by adding a Data Services layer to changing the entry points to these systems as per the newly defined service contract definitions.

Security and Governance

SOA also adds a new overhead as far as Security of the services is concerned. As each system is offered as a service, if proper security configurations have not been declared, any service will be able to access any other service. Let’s assume following conditions for an industrial application

• “Material Management Service” should not be accessible from a “Payroll Service”.
• “Time Sheets Service” should be accessible from a”Payroll Service”.

To fix this issue following access permissions have to be given

• Access control definition has be to set that “Time Sheets Service” should be accessible from”Payroll Service”. This does not mean “Payroll Service” can be accessed by “Time Sheets Service”.
  

The above service access permissions are given declaratively through XML configurations in most of the SOA implementations and not programmatically.

SSO and SOA

Single Sign On (SSO) has become a major part of SOA now a days. Most of the governance or roll based authentication is provided by SSO. SSO runs as a separate authentication service and other services access this service for authentication. Once the user is authenticated the user can be able to access various services as per his role.

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