Now , after having a look at at the ESB fundamentals and some other fundamental concepts , let us have a look at the ESB capabilities .
ESB – Capabilities
We approach this questions as - “ If I have an ESB deployed in my IT landscape,what are the capabilities which are added to my landscape? ”.
The added capabilities can be examined under the following classifications -
Integration
Communication
Mediation
Management
Lets look into each in detail .
Integration - Web Services
One of the primary features of ESB is its support for Services (especially Web Services).In fact , the number of web services in any landscape play a vital role in deciding whether we should use ESB as an Integration medium or other medums line Message Brokers etc. We will revisit this point in ESB Design Decisions.
ESB Exposes the abstract endpoint of the registered integrated service so that service is consumed by sending a message to the ESB endpoint
Uses the awareness of interface, protocol and data format and uses internal Service Invocation framework to translates message send/receive into a call to the underlying service.
Achieves Service Virtualization by exposing service endpointsfor discovery
Maintains an internal registryused for routing and storing service metadata
Provides Light weight service orchestration i.e. Coordinationof multiple implementation services to expose as a single, aggregate service that in turn can be used by service orchestration layer of a composite application.
Provides Error Handling - ability to capture and process faults at service, pipeline and other stages
Provides authentication and authorization features,transport and message level security, auditing of activities on services and Single sign on.
Integration – Protocol Transformations
Maps and transforms into appropriate protocol required by the end-point service, allowing for dynamic run-time protocol switching
Integration – Adaptors
Use of Adapters, to enable connectivity into packaged and custom enterprise applications, as well as leading technologies. For example, Legacy , Packaged Applications, technologies such as EJB can mr made to communicate via adaptors.
ESB also achieves protocol and data transformation required by the connected enterprise system
In the diagram above, we see ESB integrating with four EIS systems.There are fours tpyes of adaptors here .The top most adaptor is in-build in the EIS system itself(provided by the software vendor), second adaptor is third party vendor , third adaptor is build using ESB while the fourth adaptor is available out of the box with ESB itself.
Communication - Addressing
ESB can interpret the Physical location or network address of the service and facilitate routing
Communication - Transportation
Support for a range of protocols (JMS, WS, FILE, FTP, HTTP(S), SMTP, EMAIL)
Can match the requestor to a provider of service based on protocol supported
IIf need be performs protocol switch when a providers functionality and QoS meets the needs of the requestor
Communication - Bindings
ESB provides Support for a range of bindings (XML/SOAP/Text/Binary/MFL/Attachments)
Communication - Routings
ESB outes of requests to the relevant service provider. Involves find/bind/invoke operations i.e. identifying and locating the next service in the chain, binding to it, and invocation of it
It maintains location transparency from the perspective of a requestor.
Provides Static Routing by looking up service endpoint in ESB Namespace Directory or Routing information table in database where the Itinerary defining which endpoint to visit is mentioned in the message
Provides Dynamic Routing by examining message content and configured rules for content based routing
Updates externalized routing directory shields the requester of any changes to the provider location
Provides Intelligent routing based on infrastructure intelligence (availability, workload) or detection of error situations is also feasible but complex
It provides Synchronous & Asynchronous Message Processing,Multiple message exchange patterns (request/response, publish/subscribe, fire-and-forget) , Validation, Transformation, Enrichment and Persistence.
Mediation
Mediation is the capability that facilitates systematic and seamless service based interaction between requestor and provider.It consists of Flows or Logic that are applied on or operate on messages as they flow through the system. Typically they satisfy the integration and operational requirements
The Contract between the requestor and provider of the service are realized by using a set of mediation modules
In any ESB , set of pre-built mediation modules(e.g. transformation, lookup, filter, logging) are usually available and the capability to build custom mediationfunctions is also provided
ESB serves as the Service Mediation layer and enables -
Transport Protocol–Interaction with services over multipletransport protocols.
Data Conversion–Data transformationbetween interacting services. Runtime Policy Enforcement-Point of enforcementof runtime rules(like security etc.) on interacting services.
Pipeline Processing–Application offilters and routing ruleson messages that are easily configurable to facilitate service interaction.
Loose Coupling–De-coupling of service consumer(client) and service provider, so that any changes to either of them is masked from rest of the interacting services
Mediations can be inserted at different points on a service interaction link
At requestor end - Mediation performed irrespective of which provider the requestor interacts with e.g. encryption of sensitive information or intelligent routing
At provider end - Mediation performed irrespective of which requestor send the request e.g. Protocol or format conversion based on provider‟s requirements
With a particular interaction link - Mediation performed for interactions that occur through this link e.g. audit logs creation
Management
ESB provides the following management featues
Administration
ESB endpoint and registry integration, management, and publication preferably with an Administration Console
Managing changes and versions of services being published
Configuring audit on message saves, edits and resubmits and maintaining the log history
Monitoring
Identify dependencies that exist between different services, trace service interactions, and identify root causes of performance bottlenecks or failures
Exception Mediation
View of the messages that raised faults through the console
Message repair options to edit the faulty message and resubmit
Alert subscription and Notifications on error for user groups
Service Levels
Provide visibility into service utilization and other service metrics like response time and faults
