Service Oriented Architecture and Web Services represent a significant opportunity to develop business systems that can adapt to business requirements in a timely and effective manner. However, operational characteristics of real SOA deployments may derail much of the expected return on investment.
Service virtualization addresses the critical operational, integration and life cycle issues that can derail or delay Service Oriented Architecture implementations. Without addressing these issues through service virtualization and it’s supporting abstraction layer, many of the benefits of an SOA are constrained at best and at worst, may not be achieved at all.
2006, Reactivity, Inc.ABSTRACT Load balancers, name servers (e.g. DNS), even stock brokerage services are existing examples of virtual services in the worlds of networking and financial services. In the arena of Service Oriented Architectures (SOA), virtual services and their supporting abstraction layer are critical to address the operational, integration,security and life cycle issues that delay and derail SOA deployment and success. This paper will introduce the concept of virtual services for SOAs and provide details of the characteristics of virtual services that enable SOA success.Authored by Andrew Nash,Chief Technology Officer, ReactivityService VirtualizationKey to Managing Change in SOAUntitled Document 2006, Reactivity, Inc. www.reactivity.com Service Virtualization | 2WHITEPAPERContentsVirtualization and Abstraction 3Stock Brokerage Services ....................................................................3Networking Services.............................................................................3So What is a Virtual Service? 4The Promises of Service Oriented Architecture 4Loose Coupling at least a minor grail .........................................5Change Happens 5Service Versioning .................................................................................6Service Retirement ................................................................................6New Versions of Standards .................................................................6Optional Subsets within Standards .................................................6Increased Sophistication and Governance Requirements .....7Every Service Consumer is Different ...............................................7Geographical Constraints ...................................................................7 Legacy Implementations ....................................................................8Virtual Services 8Service Abstraction Layer 9Addressing and Location .................................................................10Routing and Filters .............................................................................10Data Hiding and Privacy ...................................................................10Security Mechanisms ........................................................................10Mapping and Translation .................................................................10Transport Mediation ..........................................................................10Load Balancing and Failover ...........................................................10Virtual Service and Policy Control of Application Systems ..11Adding SOA Components 11Getting Started with Virtual Services 12For More Information 12Untitled Document 2006, Reactivity, Inc. www.reactivity.com Service Virtualization | 3WHITEPAPERService Oriented Architecture and Web Services represent a significant opportunity to develop business systems that can adapt to business requirements in a timely and effective manner. However, operational characteristics of real SOA deployments may derail much of the expected return on investment. Service virtualization addresses the critical operational, integration and life cycle issues that can derail or delay Service Oriented Architecture implementations. Without addressing these issues through service virtualization and it s supporting abstraction layer, many of the benefits of an SOA are constrained at best and at worst, may not be achieved at all.This white paper is part of a series describing policy, deployment and operational issues and solutions associated with Service Oriented Architectures and Web Services. The overview paper, Architecting the Infrastructure for SOA and XML provides a useful introduction to the broader topic areas.Virtualization and AbstractionVirtual services abound in the real world, although often we are so familiar with them that we do not recognize them as such.Stock Brokerage ServicesIn the world of stock trading many different exchanges exist for companies to list with, but few of us are aware of them, and even few of us are in a position to trade on their implemented services directly. Instead we use a virtual service known as a stock broker, who handles requests to buy or sell stock in companies irrespective of what stock exchange a company is listed on. We rely on him to handle the various rules of the exchanges, to correctly handle the interfaces for settlement of trades. We expect stock brokerage services to provide added values such as aggregating transactions and monitoring the transaction for completeness and for tax reporting purposes. Stock brokers are expected to know when changes occur like the movement of a company stock listing from one board or exchange to another, and to analyze the flow of trades to make recommendations about the likely direction that future trading will take.In this analogy, stock exchanges provide concrete or implemented services; the broker provides a virtual service; and the additional values that we derive are provided by the abstraction layer provided by the stock broker.Networking ServicesVirtual service examples that we are familiar with in the networking world include services such as name servers and load balancers. A name server (e.g. DNS) allows a network node to maintain a known stable name by which it accessed by even when its network address is changed. Changes to the address or location of the node are concealed from applications using the DNS name to access a network node. Application developers do not need to understand how the network infrastructure works, and are not required to include additional complexity in their code to handle exception events or provide configuration and management. The virtual service is the exposed or published DNS name of the network node, while the implemented service is the physical node being accessed. The abstraction layer provided by the DNS includes value added capabilities such as caching to reduce the cost of name translations.Similarly, a load balancer exposes a single virtual instance of a server identity while supporting multiple instances of the implemented server. The load balancer abstraction layer then provides additional value by distributing the load for the virtual service in various ways across implemented services, or providing fault detection and failover to handle loss of an implemented service. In each of these cases, there is a virtual or exposed service that we interact with (generally through a publication or discovery process), and then instances in various forms of the actual implemented service that supply the physical service. In Untitled Document 2006, Reactivity, Inc. www.reactivity.com Service Virtualization | WHITEPAPERaddition, in each case, there is an abstraction layer that provides the logic that handles change, or adds value on top of the originally exposed service. The naming service abstraction layer simply makes and distributes changes in addresses. The load balancer abstraction layer takes care of load distribution, fail over and fault detection.So What is a Virtual Service?The concept of a virtual service is simple but powerful. When a service is implemented, a service contract is created defining attributes that describe how a service consumer should interact with the service interface.1 Rather than directly publish this implemented service interface with it service contract, an alternate service interface with a different address is published and deployed. This virtual service interface may define a different collection of attributes defining a new (but closely related) service contract that define unique aspects of the usage requirements of the service instance. An abstraction layer operates between the virtual service interface and the implemented service interface to harmonize differences between the interfaces, perform transformations as required, integrate with other infrastructures and allow policy based changes to be made.Minimally, this affords an opportunity to change the address of the implemented service without affecting its dependant consumers. However, the supporting abstraction layer provides a much richer set of opportunities - not the least of which are policy controls that change or modify the capabilities of the published interface without recoding the service implementation. Different security mechanisms, credential types, messaging models, and protocols can be supported on a per published interface basis, and may be changed dependant on the associated service consumer needs.A virtual service and the supporting abstraction layer effectively create a container or policy enforcement point where policy can be used to select appropriate options that deal with the variability across service versions, supporting platform implementations, trust domains and organizational structures.The Promises of Service Oriented ArchitectureService Oriented Architecture (SOA) defines a model where business or technical services are offered to consumers forming a distributed application system. The coarse granularity of this services view, as opposed to defining objects and methods, creates an architecture where logical business functions are reusable. The business benefits of this architecture include:" increased business agility " a wider set of connected customers and partners " better business alignment" improved customer satisfaction " reduced integration and operating costsThe technical benefits include: " efficient development " functionality reuse " more effective maintenance " incremental adoption " controlled system enhancement1 It is important to note that the service contract describes the application level interface requirements. This will often be defined using a WSDL description. However, there are many underlying components of the XML stack that are not expressed in this form. Some of these are likely to be covered as various derivatives of WS-Policy are created, but many integration and interoperability challenges will remain for some time to come. Untitled Document 2006, Reactivity, Inc. www.reactivity.com Service Virtualization | 5WHITEPAPERLoose Coupling at least a minor grailOne of the more significant architectural attributes of an SOA is Loose Coupling . Loose coupling defines a model where the interface to access a service and the supporting implementation are separated. This is shown in Figure 1. Dependencies between a service implementation and a service consumer are minimized, as are dependencies on other parts of the system ensuring that service reuse can be maximized. The service interface is maintained as a stable reference, while underlying implementation changes such as bug fixes are applied or alternative algorithms or processes are defined within the implementation.This is a very powerful concept if executed correctly. Much of the power of an SOA is derived from appropriately defined loosely coupled services. One measure of effectiveness for an SOA is not the number of services defined or how quickly they are implemented, but rather how many times a particular service is reused. The high level of reuse of services leads to speedy development of new business systems and in turn to support of business agility.The ultimate goal for many architects implementing loosely coupled services may be measured by the ultimate amount of unexpected or unplanned reuse of a service. An effective, loosely coupled service, deployed at the right level of granularity can be expected to be leveraged in ways that the original designer had not conceived of.2Change HappensLoose coupling principals are extremely valuable at the level of an individual service. However, in the process of building a fully operational application system from Web Services, there are many other types of change that must be facilitated, including: ServiceInterfaceServiceImplementationServiceConsumerServiceContractUDDIWSDLFigure 1 Loose Coupling - Service Interface and Implementation Separation2 Of course there are security, governance, privacy and a host of other issues that must be resolved in real deployments that constrain this view. However, the value of virtual services and their policy driven abstraction layer is that an enforcement point is provided where control can be maintained and monitored.Untitled Document 2006, Reactivity, Inc. www.reactivity.com Service Virtualization | 6WHITEPAPER" Service versioning" Service retirement" Introduction of updated standards" Selection of optional subsets within standards" Increasing sophistication and governance requirements" Varying service consumer needs" Different geographical constraints" Integrating legacy implementationsService VersioningOver time, any given service interface is likely to be enhanced or require changes. Current logic says that a new service definition or version can be declared, published to a repository such as UDDI and then located dynamically by the service consumer and then a connection established. However, for many deployments, the location or selection of a web service is done at development time, not run time. This means that the service consumer needs to be recompiled, tested, QA d and deployed in order to deal with changes in the interface. For the provider of the service there is also a growing problem. Multiple versions of an interface and the supporting implementations now have to be supported. It would be preferable in many cases to support multiple virtual instances of a service that map back to a single deployed service interface and implementation.In this case an abstraction layer would handle mapping and mediation and transformation activities to handle the differences between versions. In addition, it would handle filtering on service addresses or message contents and routing messages to the appropriate implemented service.Service RetirementAs reuse of services becomes more common, the collection of consumers utilizing a given service will grow. Particularly where the consumers are not directly under the administrative control of the provider of the service (e.g. partners, customers, or users from other business units) it is difficult to control how quickly such consumers are moved off early versions of a service that a provider wishes to retire. This leads to an increased support burden on the service provider. To handle this challenge, it must be possible to verify the collection of consumers that may be using a service. Logging and monitoring capabilities in the abstraction layer should provide this information for administrative tracking as well as auditing and compliance reasons.A phased retirement requires that users of older versions be routed to newer versions, with appropriate semantic and syntactic transformations applied as appropriate. Where automatic translation can not be performed, or to handle requests to a service that has been put through end of life, appropriate error responses need to be returned to the service consumers by the abstraction layer.New Versions of StandardsThe state of Web Service standards development is very fluid. In almost every area of standardization, there are upcoming releases. Standards such as SAML have released multiple versions that are not backwards compatible. Often, capabilities and mechanisms provided by such standards are not expressed in a controllable way within the service contract established between the service and the consumer.Even if all implementations of standards were perfectly interoperable (which they certainly are not) the introduction of new versions leads to incompatibilities or the use of advanced capabilities that one side or the other in a service exchange may not be able to handle. An abstraction layer supports uncoupled deployment of new standards on each side of a web service interaction without requiring that all participants upgrade in a synchronized manner. Optional Subsets within StandardsEven in a near perfect world where the same versions of all standards were in use across all platforms, development environments and application standards typically allow selection of different options. For example, there are different authentication tokens or canonicalization types, message Untitled Document 2006, Reactivity, Inc. www.reactivity.com Service Virtualization | 7WHITEPAPERexchange patters, protocol bindings, or dozens of others. Negotiation of optional subsets will be assisted over time by the WS-Policy framework, but there are many such choices that need to be managed and not enough support at this time. Further, the decisions as to what subsets are negotiated under what sets of criteria should be a policy decision, not left to individual implementers. Polices will change over time, and the next collection of service consumers may require special handling.The service abstraction layer provides a well defined location where policies can be established or modified. As such it also provides a valuable location for monitoring the application of the policy for operational and auditing purposes.Increased Sophistication and Governance RequirementsEarly deployment of all new IT technologies (at least successful ones) such as Web Services tend to follow a similar adoption pattern that of least technology deployment. Organizations tend to use the smallest subset of the technology that they reasonably can in order deploy an operational system. Taking security as an example, the simplest model for securing a Web Service is to deploy existing session based security mechanisms such as SSL/TLS or VPN s. It often takes pressure from other requirements such as privacy or auditing requirements to cause movement to a more sophisticated mechanism such the message level security features of the Web Services Security Standard.Pressures from business needs, partner requirements, governance or regulatory controls often cause a reevaluation of the simple early technologies deployed. The impact of such changes is often costly if implemented services need to be recoded to support more sophisticated mechanisms and their operational needs. A service abstraction layer allows new mechanisms to be deployed on behalf of the virtual service by plugging in the required mechanisms and integration with supporting infrastructures. In most cases, this can be handled without changing the implemented service.Every Service Consumer is DifferentThe business agility that is sought from web services is often thought of in terms of rapid production of new business services by leveraging other composable web services. However, this is only addresses the first part of the agility requirement. Getting the first business partner or client actively using the service is the next step and often requires a significant amount of debugging support.More importantly, is how quickly can the second, third and many follow on new business clients also be brought up to speed. Service provisioning or consumer on-ramping tends to be complicated by the fact that every consumer has some slightly different set of needs or capabilities. Some may have only simple IAM capabilities and be able to provide only username and password authentication mechanisms rather than the SAML credential type you had agreed with the first client. Others may require the use of Kerberos tickets or X.509 Certificates. Others may require that all transactions are signed or encrypted for integrity or privacy reasons. Still others may demand a higher level of SLA and verification that those terms are being met.In all of these cases, the abstraction layer should handle the changes and differences that are demanded. For the first consumer, it should provide monitoring and debug facilities to eliminate the bugs in the service contract and implementation. For the follow on consumers, it must mediate the different requirements and mechanisms preferably without impacting the implemented service.Geographical ConstraintsFor enterprises operating across many geographies, compliance with regulatory requirements can be challenging. Specific regions such as the European Union place particular privacy and other regulatory requirements on the information that is transferred out side of EU countries. Untitled Document 2006, Reactivity, Inc. www.reactivity.com Service Virtualization | 8WHITEPAPERAn abstraction layer should provide the facilities to filter and then obfuscate, remove or remap private or sensitive information as it is transferred across these geographic boundaries. This processing may be required on behalf of services offered within a geography to consumers outside of it, or on behalf of consumers with similar requirements.Legacy ImplementationsFinally, Web Services and the support of SOA has been evolving over the last five years. There are many implementations of XML over Message Queues (MQSeries, JMS etc.), or XML documents sent in raw HTTP payloads. SOAP itself has been progressively moving from RPC to document oriented mechanisms as a preferred messaging model. Progressively more sophisticated message exchange patterns are beginning to appear. The division between architects and implementers who prefer RESTful as opposed to SOAP based Web Service continues. Adoption of a wider set of protocols such as SMTP (for store and forward or long lived transaction models supporting ebXML) or FTP (for transfer of large data sets or attachments) is occurring.In, addition, the usefulness of web services deployments is often dependant on effective integration with other infrastructures such as data repositories, enterprise service busses, message queues and identity and access management systems.An abstraction layer should handle the mediation between the various protocols, handling buffering for store and forward mechanisms and integrate with other required supporting infrastructures.Virtual Services A virtual service is the exposed interface that a consumer should connect to. Many different virtual services may be deployed to meet the requirements and changes of the collection of Figure 2 Virtual ServicesAbstractionLayerServiceInterfaceServiceConsumerV3 ServiceImplementationV3SAMLServiceConsumerV3Username/ PasswordServiceConsumerV2X.509 CertificateServiceConsumerV1Username/PasswordUDDIServiceContractUDDIServiceContractUntitled Document 2006, Reactivity, Inc. www.reactivity.com Service Virtualization | 9WHITEPAPERconsumers that arise over time. The supporting abstraction layer provides the underlying policy driven mechanisms that allow virtual services to effectively provide the generality required in an operational deployment. It also handles changes in underlying standards or mechanisms to reduce or remove any impact on the implemented back end service maintainers.So, much of the magic that happens that enables virtual services lies in the domain of the abstraction layer. Simply publishing additional interface descriptions is not sufficient; logic and transformation have to be applied to marry the virtual and actual service together. Let s take a look at the capabilities and mechanisms that an abstraction layer should support.Service Abstraction LayerThe published virtual service interface that is used by a given service consumer will in most cases use a repository such as UDDI as its publication mechanism. Descriptions of many of the service requirements will be defined using WSDL. However, the use of underlying support capabilities such as the versions or subsets of particular standards in use can not be fully captured at this time.A range of supporting information may be specified describing the linkages, transformations and requirements to deploy the virtual service interfaces. Examples of support information may include:" Addressing and location information" Routing and filters" Data hiding / privacy constraints" Security mechanisms" Mapping and translation descriptions" Transport mapping" Load balancing and failover notificationsFigure 3 shows the abstraction layer and functional capabilities. Each of these is worth considering in a little more detail.Figure 3 Service Abstraction LayerLoadBalancingFailoverV3SAMLV3 ServiceImplementationServiceConsumerV2X.509 CertServiceConsumerIdentity &Access ControlPolicyEnforcementLoginMonitoringSecurityPrivacyTransformFilteringRoutingV3 ServiceImplementationV3 ServiceImplementationUntitled Document 2006, Reactivity, Inc. www.reactivity.com Service Virtualization | 10WHITEPAPERAddressing and LocationEach virtual service interface can be named and located through a number of different mechanisms, although UDDI is the most likely publication and discovery mechanism. However, the value of the abstraction layer is that the name of the associated service may be changed, the address may be modified or the number of instances of a particular service deployed may vary.Routing and FiltersThe description of how a virtual service is linked to its associated implemented service may take several forms. The simplest is describing the name or address of the target service corresponding to the published virtual service. However other forms of routing information may be utilized that support additional linkage information, or filters describing message contents that may be used to support a dynamic routing decision.Data Hiding and PrivacyAn implemented service may be deployed as a virtual service in different administrative domains. Information that may be validly exposed within an enterprise should not be allowed to transit enterprise boundaries. Message fields that should be kept hidden or private may be defined and removed or obfuscated in various ways for different service consumers. Security MechanismsAs a service is invoked by different consumers in different trust domains, a range of different security mechanisms may be applied. For example, internal consumers of a web service may only be required to provide a username and password as an authentication credential. External consumers of the service might have a choice of SAML or X.509 certificates as credentials. Internal use of a service may not require a signed or encrypted payload, but the same information moving across an enterprise boundary may require either or both mechanisms to be applied.The abstraction layer provides policy based control of the type of authentication credential used and when they are required, how they are mapped and what security transforms (e.g. signing or encryption) are required on particular services or messages.Mapping and TranslationIn order to support differences in versions between published virtual services and the implemented service, it may be necessary to transform the messages that are passed between the virtual service interface and the implemented service interface. This may require removing, translating, mapping or inclusion of fields within a message. This support may also require access to additional data repositories such as directories or databases. Transport MediationFor integration purposes many different types of transport may need to be tied together. Examples may include a legacy XML service that has been deployed over a message queue, or a new consumer that only support the use of XML within HTTP messages and not SOAP.The abstraction layer handles all of the issues required to mediate between the various types of transports.Load Balancing and FailoverThe number of instances of an implemented service that support a published virtual service may vary to meet transaction load requirements or to provide a failover3 mechanism if a service instance on a given platform should fail. In addition to routing, the abstraction layer may provide load balancing capabilities to distribute the message load across the implemented services. Failure of a service may also be detected to allow redirection to a standby version of the service running at some other location. 3 Service load balancing and failover operates at a different level to network load balancing. Service load balancing is looking to determine if a given service is operating correctly independent of the network level processing of arriving packets.Untitled Document 2006, Reactivity, Inc. www.reactivity.com Service Virtualization | 11WHITEPAPERVirtual Service and Policy Control of Application SystemsThe virtual service and the abstraction layer supporting it provide significant policy enforcement and instrumentation points for control and monitoring purposes. Figure shows how many virtual services and the abstraction layer processing associated with them are linked to centralized policy management, distribution, monitoring and auditing facilities.Policies may be defined and enforced at the virtual service that handle transformation, security, privacy, integrity and many other mechanisms. Any of the abstraction layer capabilities described above may be defined as a policy that is enforced consistently across application platforms. As policy is being enforced, and messages are being transformed in various ways, as ideal opportunity to instrument the behavior of the service is provided. Data collected about the operation of the virtual service and the messages passing through the abstraction layer allow support of Service Level Agreements, service testing, monitoring, auditing and logging record generation.Adding SOA ComponentsTo practically deliver results with SOA, the enterprise needs a scalable mechanism to support service virtualization and provide the abstraction layer for security, interoperability and visibility across the network of services. As the deployment of SOA and Web Services progresses, scaling or complexity management requirements may lead to augmenting the service abstraction layer with repositories for publication, discovery services for locating appropriate web services, SLA definition and management tools and other components.In the context of virtual services, all of these components continue to offer the same functionality and value. However, from the perspective of the service consumer, the services that are supported, published, discovered etc. are the virtual services. Figure 4 Policy enforcement and monitoring pointsServiceConsumer= Implemented Service Interface= Virtual Service InterfacePolicy AdministrationMonitoring AuditingEnforcementPointServiceConsumerEnforcementPointServiceConsumerEnforcementPointUntitled Document 2006, Reactivity, Inc. www.reactivity.com Service Virtualization | 12WHITEPAPERSo virtual service interfaces and the WSDL or WS-Policy derived components may be described and published in a UDDI that is accessed by a service consumer. Service discovery would locate and identify the virtual services. SLA management would reference the service interface provided by the virtual interface defined for the service consumer. A workflow manager or business process language engine would operate on the virtual services defined.If an organization has decided that any of these supporting SOA or Web Services infrastructure services is appropriate in deploying an SOA, they continue to operate unchanged. However, all of the supporting abstraction layer benefits discussed above providing a secure, robust, and flexible system enhance these components and the SOA as a whole.Getting Started with Virtual ServicesWhat do you need to consider when establishing your first virtual services in support of your Enterprise SOA?Virtual service concepts can be applied effectively with significant return irrespective of the size or complexity of your SOA or Web Service deployment. As the concepts and mechanisms are designed to buffer you against change and to expedite your deployments, they have value whether you have a single web service with one or multiple consumers, or hundreds of web services in deployment.For enterprise architects designing an SOA, virtual services and the abstraction layer provide known, well defined locations for policy control and monitoring. For project architects and implementers, virtual services provide a control point where changes can be defined and monitored without the need to redesign, code, QA and redeploy. For operations staff, virtual services provide a control boundary for applying changes under policy control to support on-ramping new customers or service consumers. It also provides the monitoring points to identify issues that may arise or the need for additional capacity.The Reactivity XML Gateway products are designed explicitly to provide a virtual service model. The gateways provide a virtual service abstraction layer where message transformation, protocol translation, syntactic and semantic mediation and security validation and processing take place. The extensibility, speed and security of the Gateways ensures that this abstraction layer increases the value of services connecting in the SOA. Service contracts and descriptions for implemented services in the form of WSDL s may be imported from a UDDI directory or other sources, enhanced to apply specific policy requirements and then republished as a virtual service interface. The Gateways act as policy enforcement and monitoring points to allow consistent policy application across all services and to monitor and audit application system behavior.For enterprises beginning to deploy web services, virtual services and the supporting abstraction layer allow fast deployment of early web services to prove the concepts and show a return on investments that supports the business case for continued investment and deployment of web services and SOA.For More InformationTo learn more about Reactivity s secure XML infrastructure Gateways and determine how they can provide scalable, service virtualization to maximize the value of your XML Web Services and SOA, contact Reactivity at 1-866-889-3 85 or email@example.com.