Addressing Instances
Addressing an Instance
Each instance of the application has a service ID, whose value can be set with
spring.cloud.bus.id and whose value is expected to be a colon-separated list of
identifiers, in order from least specific to most specific. The default value is
constructed from the environment as a combination of the spring.application.name and
server.port (or spring.application.index, if set). The default value of the ID is
constructed in the form of app:index:id, where:
-
appis thevcap.application.name, if it exists, orspring.application.name -
indexis thevcap.application.instance_index, if it exists,spring.application.index,local.server.port,server.port, or0(in that order). -
idis thevcap.application.instance_id, if it exists, or a random value.
The HTTP endpoints accept a “destination” path parameter, such as
/busrefresh/customers:9000, where destination is a service ID. If the ID
is owned by an instance on the bus, it processes the message, and all other instances
ignore it.
Addressing All Instances of a Service
The “destination” parameter is used in a Spring PathMatcher (with the path separator
as a colon — :) to determine if an instance processes the message. Using the example
from earlier, /busenv/customers:** targets all instances of the
“customers” service regardless of the rest of the service ID.
Service ID Must Be Unique
The bus tries twice to eliminate processing an event — once from the original
ApplicationEvent and once from the queue. To do so, it checks the sending service ID
against the current service ID. If multiple instances of a service have the same ID,
events are not processed. When running on a local machine, each service is on a different
port, and that port is part of the ID. Cloud Foundry supplies an index to differentiate.
To ensure that the ID is unique outside Cloud Foundry, set spring.application.index to
something unique for each instance of a service.