An enterprise service bus (ESB) is a software architecture construct
that enables communication among various applications. Instead of having
to make each of your applications communicate directly with each other
in all their various formats, each application simply communicates with
the ESB, which handles transforming and routing the messages to their
appropriate destinations.
This is the Formal Definition of ESB by WSO2 So Let's see the Word ESB and how its doing the Works.
Enterprise : the concept has been originally invented to reduce complexity of enterprise application integration (EAI) within an enterprise; the restriction has become obsolete since modern Internet communication is not limited to a corporate entity only.
Service :denotes noniterative and autonomously executing programs that communicate with other services through message exchange
Bus : is used in analogy to a computer hardware bus
Why ESB?
- Individual software applications cannot achieve much
- Systems should be integrated to work together
- Enables free data flow across the organization, data sharing and unified data
views - Improves production and management efficiency through reuse of existing
services - Application users can make better decisions using universal information rather
than isolated fragmentary information - Proper feedback loop to enhance business operations, with integrated activity
monitoring
How ESB Works
- An application sends a message to the ESB.
- The message is picked up by a transport.
- The
transport sends the message through a message pipe, which handles
quality of service aspects such as security. Internally, this pipe is
the in-flow and out-flow of Axis2. The ESB can operate in two modes:
- Mediating Messages - A single pipe is used.
- Proxy Services - Separate pipes connecting the transport to different proxy services are used.
- Both message transformation and routing can be considered as a single unit. As the diagram specifies, there is no clear separation between message transformation components and routing components. In WSO2 ESB, this is known as the mediation framework. Some transformations take place before the routing decision has been made while others take place after the routing decision. This is part of the Synapse implementation.
- The message is injected to the separate pipes depending on the destinations. Here again, quality of service aspects of the messages are determined.
- The transport layer takes care of the transport protocol transformations required by the ESB.
WSO2 ESB Architecture
Transports
A transport is responsible for carrying messages that are in a specific format. WSO2 ESB supports all the widely used transports including HTTP/s, JMS, and VFS, and domain-specific transports like FIX. You can easily add a new transport using the Axis2 transport framework and plug it into the ESB.Transports include the following components:
- Message builders - Identify the message using the content type and convert it to common XML. There is a message builder associated with each content type. WSO2 ESB includes message builders for text-based and binary content.
- Message formatters - The opposite partners of the message builders. The formatter converts the message back to its original format by referencing the content type just before the message handover to the transports.
See Working with Transports.
Endpoints
An endpoint defines an external destination (such as a service) for a message. An endpoint can be specified as an address endpoint, WSDL endpoint, a load balancing endpoint , and more. An endpoint is defined independently of transports, allowing you to use the same endpoint with multiple transports. When you configure a message mediation sequence or a proxy service to handle the incoming message, you specify the transport to use and the endpoint where the message will be sent.See Working with Endpoints.
Proxy Services
Proxy services are virtual services that receive messages and optionally process them before forwarding them to a service at a given endpoint. This approach allows you to perform necessary transformations and introduce additional functionality without changing your existing service. Any available transport can be used to receive and send messages from the proxy services.See Working with Proxy Services.
APIs
An
API in WSO2 ESB is analogous to a web application deployed in the ESB
runtime. Each API is anchored at a user-defined URL context, much like
how a web application deployed in a servlet container is anchored at a
fixed URL context. An API will only process requests that fall under its
URL context. The API defines one or more resources, which is a logical component of an API that can be accessed by making a particular type of HTTP call. This approach allows you to send messages directly into the ESB using REST.
See Creating APIs.Topics
A topic allows services to receive messages when a specific type of event occurs by subscribing to messages that have been published to a specific topic.See Working with Topics and Events.
Mediators
Mediators are individual processing units that perform a specific function, such as sending or filtering messages. WSO2 ESB includes a comprehensive mediator library that provides functionality for implementing widely used enterprise integration patterns (EIPs). You can also easily write a custom mediator to provide additional functionality using various technologies such as Java, scripting, and Spring.See Mediators.
Sequences
Sequences are the configuration component for mediators. Sequences allow you to organize mediators to implement pipes and filter patterns.See Mediation Sequences.
Tasks and Commands
Tasks allow you to configure scheduled jobs in the ESB and execute internal and external commands for mediation.See Working with Tasks.
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