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= Spring Platform Bus
Spring Cloud Bus links nodes of a distributed system with a lightweight message broker. This can then be used to broadcast state changes (e.g. configuration changes) or other management instructions. A key idea is that the Bus is like a distributed Actuator for a Spring Boot application that is scaled out, but it can also be used as a communication channel between apps. The only implementation currently is with an AMQP broker as the transport, but the same basic feature set (and some more depending on the transport) is on the roadmap for other transports.
== Quick Start
Spring Cloud Bus works by adding Spring Boot autconfiguration if it detects itself on the classpath. All you need to do to enable the bus is to add `spring-cloud-starter-bus-amqp` to your dependency management and Spring Cloud takes care of the rest. Make sure RabbitMQ is available and configured to provide a `ConnectionFactory`: running on localhost you shouldn't have to do anything, but if you are running remotely use Spring Cloud Connectors, or Spring Boot conventions to define the broker credentials, e.g.
.application.yml
----
spring:
rabbitmq:
host: mybroker.com
port: 5672
username: user
password: secret
----
The bus currently supports sending messages to all nodes listening or all nodes for a particular service (as defined by Eureka). More selector criteria will be added in the future (ie. only service X nodes in data center Y, etc...). The http endpoints are under the `/bus/*` actuator namespace. There are currently two implemented. The first, `/bus/env`, sends key/values pairs to update each nodes Spring Environment. The second, `/bus/refresh`, will reload each application's configuration, just as if they had all been pinged on their `/refresh` endpoint.