Spring Cloud provides tools for developers to quickly build some of the common patterns in distributed systems (e.g. configuration management, service discovery, circuit breakers, intelligent routing, micro-proxy, control bus, one-time tokens, global locks, leadership election, distributed sessions, cluster state). Coordination of distributed systems leads to boiler plate patterns, and using Spring Cloud developers can quickly stand up services and applications that implement those patterns. They will work well in any distributed environment, including the developer's own laptop, bare metal data centres, and managed platforms such as Cloud Foundry.
Spring Cloud builds on Spring Boot by providing a bunch of libraries that enhance the behaviour of an application when added to the classpath. You can take advantage of the basic default behaviour to get started really quickly, and then when you need to, you can configure or extend to create a custom solution.
The release train label (see below) is actually only used explicitly in one artifact: "spring-cloud-starter-parent" (all the others have normal "Spring" release labels tied to their parent project). The starter parent is the one you can use as a BOM for dependency management or as a parent POM (Maven only). Example using the latest version with the config client and eureka (change the artifact ids to pull in other starters):
Spring Cloud focuses on providing good out of box experience for typical use cases and extensibility mechanism to cover others.
Centralized external configuration management backed by a git repository. The configuration resources map directly to Spring `Environment` but could be used by non-Spring applications if desired.
Integration with various Netflix OSS components (Eureka, Hystrix, Zuul, Archaius, etc.).
An event bus for linking services and service instances together with distributed messaging. Useful for propagating state changes across a cluster (e.g. config change events).
Integrates your application with Pivotal Cloudfoundry. Provides a service discovery implementation and also makes it easy to implement SSO and OAuth2 protected resources, and also to create a Cloudfoundry service broker.
Leadership election and common stateful patterns with an abstraction and implementation for Zookeeper, Redis, Hazelcast, Consul.
Provides support for load-balanced OAuth2 rest client and authentication header relays in a Zuul proxy.
Distributed tracing for Spring Cloud applications, compatible with Zipkin, HTrace and log-based (e.g. ELK) tracing.
A cloud native programming and operating model for composable data microservices on a structured platform.
Messaging microservices with Redis, Rabbit or Kafka. Simple declarative model to send and receive messages in a Spring Cloud app.
Spring Cloud Stream Modules can be used with Spring Cloud Stream to create, build, and scale message-driven data microservices.
Easy integration with hosted Amazon Web Services. It offers a convenient way to interact with AWS provided services using well-known Spring idioms and APIs, such as the messaging or caching API. Developers can build their application around the hosted services without having to care about infrastructure or maintenance.
Makes it easy for PaaS applications in a variety of platforms to connect to backend services like databases and message brokers (the project formerly known as "Spring Cloud").
Spring Boot-style starter projects to ease dependency management for consumers of Spring Cloud. (Discontinued as a project and merged with the other projects after Angel.SR2.)
Spring Boot CLI plugin for creating Spring Cloud component applications quickly in Groovy
Spring Cloud is an umbrella project consisting of independent projects with, in principle, different release cadences. To manage the protfolio a BOM (Bill of Materials) is published with a curated set of dependencies on the individual project (see below). The release trains have names, not versions, to avoid confusion with the sub-projects. The names are an alphabetic sequence (so you can sort them chronologically) with names of London Tube stations ("Angel" is the first release, "Brixton" is the second). When point releases of the individual projects accumulate to a critical mass, or if there is a critical bug in one of them that needs to be available to everyone, the release train will push out "service releases" with names ending ".SRX", where "X" is a number.
Release train contents:
The Angel release train builds on Spring Boot 1.2.x, and is incompatible in some areas with Spring Boot 1.3.x. Brixton builds on Spring Boot 1.3.x and is similarly incompatible with 1.2.x. Some libraries and most apps built on Angel will run fine on Brixton, but changes will be required anywhere that the OAuth2 features from spring-cloud-security 1.0.x are used (they were mostly moved to Spring Boot in 1.3.0).
Use your dependency management tools to control the version. If you are using Maven remember that the first version declared wins, so declare the BOMs in order, with the first one usually being the most recent (e.g. if you want to use Spring Boot 1.3.1 with Brixton.M3, put the Boot BOM first). The same rule applies to Gradle if you use the Spring dependency management plugin.