spring-cloud-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. Starters are provided for an AMQP broker as the transport or for Kafka, 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` or `spring-cloud-starter-bus-kafka` to your dependency management and Spring Cloud takes care of the rest. Make sure the broker (RabbitMQ or Kafka) is available and configured: 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. for Rabbit

.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 may be added in the future (ie. only service X nodes in data center Y, etc...). There are also some http endpoints under the `/bus/*` actuator namespace. There are currently two implemented. The first, `/bus/env`, sends key/value pairs to update each node's Spring Environment. The second, `/bus/refresh`, will reload each application's configuration, just as if they had all been pinged on their `/refresh` endpoint.

NOTE: The Bus starters cover Rabbit and Kafka, because those are the two most common implementations, but Spring Cloud Stream is quite flexible and binder will work combined with `spring-cloud-bus`.

== Building

:jdkversion: 1.7

=== Basic Compile and Test

To build the source you will need to install JDK {jdkversion}.

Spring Cloud uses Maven for most build-related activities, and you
should be able to get off the ground quite quickly by cloning the
project you are interested in and typing

----
$ ./mvnw install
----

NOTE: You can also install Maven (>=3.3.3) yourself and run the `mvn` command
in place of `./mvnw` in the examples below. If you do that you also
might need to add `-P spring` if your local Maven settings do not
contain repository declarations for spring pre-release artifacts.

NOTE: Be aware that you might need to increase the amount of memory
available to Maven by setting a `MAVEN_OPTS` environment variable with
a value like `-Xmx512m -XX:MaxPermSize=128m`. We try to cover this in
the `.mvn` configuration, so if you find you have to do it to make a
build succeed, please raise a ticket to get the settings added to
source control.

For hints on how to build the project look in `.travis.yml` if there
is one. There should be a "script" and maybe "install" command. Also
look at the "services" section to see if any services need to be
running locally (e.g. mongo or rabbit). Ignore the git-related bits
that you might find in "before_install" since they're related to setting git
credentials and you already have those.

The projects that require middleware generally include a
`docker-compose.yml`, so consider using
https://compose.docker.io/[Docker Compose] to run the middeware servers
in Docker containers. See the README in the
https://github.com/spring-cloud-samples/scripts[scripts demo
repository] for specific instructions about the common cases of mongo,
rabbit and redis.

NOTE: If all else fails, build with the command from `.travis.yml` (usually
`./mvnw install`).

=== Documentation

The spring-cloud-build module has a "docs" profile, and if you switch
that on it will try to build asciidoc sources from
`src/main/asciidoc`. As part of that process it will look for a
`README.adoc` and process it by loading all the includes, but not
parsing or rendering it, just copying it to `${main.basedir}`
(defaults to `${basedir}`, i.e. the root of the project). If there are
any changes in the README it will then show up after a Maven build as
a modified file in the correct place. Just commit it and push the change.

=== Working with the code
If you don't have an IDE preference we would recommend that you use
https://www.springsource.com/developer/sts[Spring Tools Suite] or
https://eclipse.org[Eclipse] when working with the code. We use the
https://eclipse.org/m2e/[m2eclipse] eclipse plugin for maven support. Other IDEs and tools
should also work without issue as long as they use Maven 3.3.3 or better.

==== Importing into eclipse with m2eclipse
We recommend the https://eclipse.org/m2e/[m2eclipse] eclipse plugin when working with
eclipse. If you don't already have m2eclipse installed it is available from the "eclipse
marketplace".

NOTE: Older versions of m2e do not support Maven 3.3, so once the
projects are imported into Eclipse you will also need to tell
m2eclipse to use the right profile for the projects. If you
see many different errors related to the POMs in the projects, check
that you have an up to date installation. If you can't upgrade m2e,
add the "spring" profile to your `settings.xml`. Alternatively you can
copy the repository settings from the "spring" profile of the parent
pom into your `settings.xml`.

==== Importing into eclipse without m2eclipse
If you prefer not to use m2eclipse you can generate eclipse project metadata using the
following command:

[indent=0]
----
$ ./mvnw eclipse:eclipse
----

The generated eclipse projects can be imported by selecting `import existing projects`
from the `file` menu.

== Contributing

Spring Cloud is released under the non-restrictive Apache 2.0 license,
and follows a very standard Github development process, using Github
tracker for issues and merging pull requests into master. If you want
to contribute even something trivial please do not hesitate, but
follow the guidelines below.

=== Sign the Contributor License Agreement
Before we accept a non-trivial patch or pull request we will need you to sign the
https://cla.pivotal.io/sign/spring[Contributor License Agreement].
Signing the contributor's agreement does not grant anyone commit rights to the main
repository, but it does mean that we can accept your contributions, and you will get an
author credit if we do. Active contributors might be asked to join the core team, and
given the ability to merge pull requests.

=== Code of Conduct
This project adheres to the Contributor Covenant https://github.com/spring-cloud/spring-cloud-build/blob/master/docs/src/main/asciidoc/code-of-conduct.adoc[code of
conduct]. By participating, you are expected to uphold this code. Please report
unacceptable behavior to spring-code-of-conduct@pivotal.io.

=== Code Conventions and Housekeeping
None of these is essential for a pull request, but they will all help. They can also be
added after the original pull request but before a merge.

* Use the Spring Framework code format conventions. If you use Eclipse
you can import formatter settings using the
`eclipse-code-formatter.xml` file from the
https://raw.githubusercontent.com/spring-cloud/spring-cloud-build/master/spring-cloud-dependencies-parent/eclipse-code-formatter.xml[Spring
Cloud Build] project. If using IntelliJ, you can use the
https://plugins.jetbrains.com/plugin/6546[Eclipse Code Formatter
Plugin] to import the same file.
* Make sure all new `.java` files to have a simple Javadoc class comment with at least an
`@author` tag identifying you, and preferably at least a paragraph on what the class is
for.
* Add the ASF license header comment to all new `.java` files (copy from existing files
in the project)
* Add yourself as an `@author` to the .java files that you modify substantially (more
than cosmetic changes).
* Add some Javadocs and, if you change the namespace, some XSD doc elements.
* A few unit tests would help a lot as well -- someone has to do it.
* If no-one else is using your branch, please rebase it against the current master (or
other target branch in the main project).
* When writing a commit message please follow https://tbaggery.com/2008/04/19/a-note-about-git-commit-messages.html[these conventions],
if you are fixing an existing issue please add `Fixes gh-XXXX` at the end of the commit
message (where XXXX is the issue number).