# Enterprise Integration Patterns

**In short:** Enterprise Integration Patterns are named designs for connecting applications through messaging. Messaging is asynchronous, program-to-program communication with reliable delivery. Apache Camel supports most of these patterns.

## Explanation

Enterprise Integration Patterns describe common ways to connect separate applications using messaging. Messaging is asynchronous, program-to-program communication with reliable delivery. Asynchronous means the sender does not wait for the receiver. See the article Synchronous vs. Asynchronous Communication.

**The basic flow**

1. The sender creates a message and puts it on a channel.
2. The receiver reads the message from the channel.
3. The receiver then extracts the data from the message.

A channel is the path a message travels. See Message Channel.

**Other integration styles**

Messaging is one of several ways to integrate applications. Two others are:

- **File Transfer:** one application writes a file, and another application reads it later.
- **Shared Database:** several applications use the same schema in one physical database.

**Example patterns: channels**

- A Point-to-Point Channel delivers each message to exactly one receiver.
- Several receivers can read from such a channel at the same time. They consume different messages, and only one of them gets any given message.
- A Dead Letter Channel (Dead Letter Queue) collects messages that cannot be delivered.

**Tool support**

Apache Camel is a framework that supports most of the patterns from the Hohpe and Woolf book.

## Example

An online shop has an order application and a shipping application. The order application puts each new order on a point-to-point channel. Two shipping workers read from that channel. Each order goes to only one worker. If an order cannot be delivered, it lands in a dead letter queue, where staff can inspect it.

## Trade-offs

Messaging is asynchronous, so the sender does not wait for the receiver. Delivery is meant to be reliable. Undeliverable messages need a place to go, such as a dead letter queue, and someone has to handle them. The verified facts here do not cover other trade-offs, such as ordering or tracing.

Basic messaging flow with a dead letter queue for undeliverable messages.

```mermaid
flowchart LR
  S[Sender] -->|puts message| C[Channel]
  C -->|reads message| R[Receiver]
  C -.->|undeliverable| D[Dead Letter Queue]
```

## Checks

- The document states which integration style connects each pair of applications (messaging, file transfer or shared database).
- Channels where each message must reach only one receiver are identified as point-to-point.
- A dead letter queue or equivalent exists for messages that cannot be delivered.

## Related

- [Messaging](https://arc.fuet.ch/concepts/integration/messaging.md)
- [Message Channel](https://arc.fuet.ch/concepts/integration/message-channel.md)
- [Point-to-Point Channel](https://arc.fuet.ch/concepts/integration/point-to-point-channel.md)
- [Dead Letter Channel](https://arc.fuet.ch/concepts/integration/dead-letter-channel.md)
- [File Transfer](https://arc.fuet.ch/concepts/integration/file-transfer.md)
- [Shared Database](https://arc.fuet.ch/concepts/integration/shared-database.md)
- [Synchronous vs. Asynchronous Communication](https://arc.fuet.ch/concepts/integration/synchronous-vs-asynchronous-communication.md)
- [Integration Styles](https://arc.fuet.ch/concepts/integration/integration-styles-overview.md)

## Sources

- [Introduction - Enterprise Integration Patterns](https://www.enterpriseintegrationpatterns.com/patterns/messaging/Introduction.html) — enterpriseintegrationpatterns.com, accessed 2026-11-09
- [EIPs :: Apache Camel](https://camel.apache.org/components/4.22.x/eips/enterprise-integration-patterns.html) — camel.apache.org, accessed 2026-11-09
- [Point-to-Point Channel - Enterprise Integration Patterns](https://www.enterpriseintegrationpatterns.com/patterns/messaging/PointToPointChannel.html) — enterpriseintegrationpatterns.com, accessed 2026-11-09
- [Dead Letter Channel - Enterprise Integration Patterns](https://www.enterpriseintegrationpatterns.com/patterns/messaging/DeadLetterChannel.html) — enterpriseintegrationpatterns.com, accessed 2026-11-09