Routers, splitters, aggregators, dead letters: messaging made legible.
The Hohpe and Woolf integration patterns, drawn with their standard icons. These matter because messaging systems fail in ways that are almost impossible to describe in prose: a splitter without an aggregator, a wire tap that changes ordering, a dead letter queue nobody drains.
The pattern people skip is the dead letter path, and it is the one that causes the 3am page. If your integration diagram has no error route, it is a happy-path sketch rather than a design.
A channel and two endpoints: the vocabulary in miniature.
@startuml
!include https://raw.githubusercontent.com/plantuml-stdlib/EIP-PlantUML/main/dist/EIP-PlantUML.puml
title Simple Messaging Flow
LAYOUT_LEFT_RIGHT()
MsgChannel(input, "Input Channel")
MessageFilter(filter, "Filter")
MessageTranslator(translator, "Translator")
MsgChannel(output, "Output Channel")
Send(input, filter)
Send(filter, translator)
Send(translator, output)
@endumlRoute by message content. Where most integrations start.
@startuml
!include https://raw.githubusercontent.com/plantuml-stdlib/EIP-PlantUML/main/dist/EIP-PlantUML.puml
title Content-Based Routing
MsgChannel(input, "Incoming Orders")
ContentBasedRouter(router, "Order Router")
MsgChannel(domestic, "Domestic Orders")
MsgChannel(international, "International Orders")
MsgChannel(priority, "Priority Orders")
ServiceActivator(domesticSvc, "Domestic\nFulfillment")
ServiceActivator(intlSvc, "International\nFulfillment")
ServiceActivator(prioritySvc, "Priority\nFulfillment")
Send(input, router)
router --> domestic : country = US
router --> international : country != US
router --> priority : priority = HIGH
Send(domestic, domesticSvc)
Send(international, intlSvc)
Send(priority, prioritySvc)One publisher, many independent subscribers.
@startuml
!include https://raw.githubusercontent.com/plantuml-stdlib/EIP-PlantUML/main/dist/EIP-PlantUML.puml
title Publish-Subscribe Pattern
MessagingGateway(publisher, "Event Publisher")
PubSubChannel(topic, "Order Events")
DurableSubscriber(inventory, "Inventory Service")
DurableSubscriber(shipping, "Shipping Service")
DurableSubscriber(billing, "Billing Service")
NonDurableSubscriber(analytics, "Analytics Service")
Send(publisher, topic)
Send(topic, inventory)
Send(topic, shipping)
Send(topic, billing)
Send(topic, analytics)
@endumlSplit a message, process the parts, put them back together.
@startuml
!include https://raw.githubusercontent.com/plantuml-stdlib/EIP-PlantUML/main/dist/EIP-PlantUML.puml
title Splitter-Aggregator Pattern
LAYOUT_LEFT_RIGHT()
MsgChannel(input, "Batch Orders")
Splitter(splitter, "Order Splitter")
MsgChannel(items, "Individual Items")
ServiceActivator(process1, "Process Item")
ServiceActivator(process2, "Process Item")
ServiceActivator(process3, "Process Item")
MsgChannel(processed, "Processed Items")
Aggregator(aggregator, "Order Aggregator")
MsgChannel(output, "Complete Orders")
Send(input, splitter)
Send(splitter, items)
Send(items, process1)
Send(items, process2)A processing chain where each stage is replaceable.
@startuml
!include https://raw.githubusercontent.com/plantuml-stdlib/EIP-PlantUML/main/dist/EIP-PlantUML.puml
title Pipes and Filters Pattern
LAYOUT_LEFT_RIGHT()
ChannelAdapterLeft(source, "File\nAdapter")
MsgChannel(ch1, "")
Filter(decrypt, "Decrypt")
MsgChannel(ch2, "")
Filter(authenticate, "Authenticate")
MsgChannel(ch3, "")
Filter(validate, "Validate")
MsgChannel(ch4, "")
Filter(transform, "Transform")
MsgChannel(ch5, "")
ChannelAdapterRight(sink, "Database\nAdapter")
Async messaging that still needs an answer.
@startuml
!include https://raw.githubusercontent.com/plantuml-stdlib/EIP-PlantUML/main/dist/EIP-PlantUML.puml
title Request-Reply Pattern
MessagingGateway(client, "Client Application")
P2PChannel(requestChannel, "Request Channel")
P2PChannel(replyChannel, "Reply Channel")
ServiceActivator(service, "Order Service")
RequestReply(request, "Order Request")
Message(reply, "Order Response")
Send(client, request)
Send(request, requestChannel)
Send(requestChannel, service)
Send(service, reply)
Send(reply, replyChannel)
Send(replyChannel, client)
note right of request
Contains:What happens when a message cannot be processed. Draw this one.
@startuml
!include https://raw.githubusercontent.com/plantuml-stdlib/EIP-PlantUML/main/dist/EIP-PlantUML.puml
title Error Handling with Dead Letter Channel
MsgChannel(input, "Incoming Messages")
MessageRouter(router, "Message Router")
MsgChannel(valid, "Valid Messages")
InvalidMsgChannel(invalid, "Invalid Messages")
DeadLetterChannel(dlq, "Dead Letter Queue")
ServiceActivator(processor, "Message Processor")
ServiceActivator(errorHandler, "Error Handler")
MessageStore(store, "Message Store")
Send(input, router)
router --> valid : valid
router --> invalid : invalid format
Send(valid, processor)
processor --> dlq : processing error
Send(invalid, dlq)
Send(dlq, errorHandler)
Send(errorHandler, store)Observe traffic without changing it: for audit and monitoring.
@startuml
!include https://raw.githubusercontent.com/plantuml-stdlib/EIP-PlantUML/main/dist/EIP-PlantUML.puml
title Wire Tap for Monitoring
LAYOUT_LEFT_RIGHT()
MsgChannel(input, "Orders")
WireTap(tap, "Wire Tap")
MsgChannel(main, "Main Flow")
MsgChannel(monitor, "Monitor Flow")
ServiceActivator(processor, "Order Processor")
MessageStore(audit, "Audit Log")
Send(input, tap)
Send(tap, main)
Send(tap, monitor)
Send(main, processor)
Send(monitor, audit)
@endumlEvery template here ships in Gnomon and renders on your machine, with no account and nothing sent to a server. The browser editor is free and needs no install.