Chapter 9: The Enterprise Service Bus
As evolved from Enterprise Application Integration (EAI), ESB ensures the different components / applications work together dynamically.
- Broad level functions
o Messaging service – transporting messages, reliable communications
o Management services – apply and monitor service level and own performance rules, handling messages priorities, apply global business rules.
o Interface service – validates messages against the schema
o Mediation service – sends and converts messages between 2 connecting apps. This can be part of SOA Service Broker.
o Metadata Service – transforms data as per source and destinations apps. E.g. definition of Customer can be different for each connecting app. ESB handles it either by storing that definition locally using light-weight registry or external registry.
o Security, encryption for communication. Authentication, authorization, privacy, data integrity, audit are goals of security. ESB doesn’t implement any security, however facilitates pluggable security. It is a type of mediation service. SOA Service Broker has this responsibility.
- Core services ESB offers is messaging and management service, all other service can be duplicated, like interface service, which can be offered by other SOA layers. As ESB is more generic and needs to stand on its own, so the duplication.
Types of messaging
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Point-to-point – No response expected, message just sent
- Point-to-point request/response – Transaction not complete until response is received by sender
- Broadcast – Broadcasts messages to multiple receivers, no response expected
- Broadcast request/response – only difference from above is that, transaction isn’t complete until all responses received for requests sent.
- Publish/subscribe – Messages received by those who subscribe to receive the messages published at agreed place.
- Store/forward – if recipient doesn’t get sent messages, this type will store messages and forwards once receiver becomes online.
- Runtime ESB - ESB doesn’t run as an island. It keeps things loose and increases reliability and predictability for connection services.
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