Spring_Cloud_Finchley.SR1

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). 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.

Version: Finchley.SR1

1. Features

Spring Cloud focuses on providing good out of box experience for typical use cases and extensibility mechanism to cover others.

 Distributed/versioned configuration

 Service registration and discovery

 Routing

 Service-to-service calls

 Load balancing

 Circuit Breakers

 Distributed messaging

Part I. Cloud Native Applications

Cloud Native is a style of application development that encourages easy adoption of best practices in the areas of continuous delivery and value-driven development. A related discipline is that of building 12-factor Applications, in which development practices are aligned with delivery and operations goals — for instance, by using declarative programming and management and monitoring. Spring Cloud facilitates

these styles of development in a number of specific ways. The starting point is a set of features to which all components in a distributed system need easy access.Many of those features are covered by Spring Boot, on which Spring Cloud builds. Some more features are delivered by Spring Cloud as two libraries: Spring Cloud Context and Spring Cloud Commons. Spring Cloud Context provides utilities and special services for the ApplicationContext of a Spring Cloud application (bootstrap context, encryption, refresh scope, and environment endpoints). Spring Cloud Commons is a set of abstractions and common classes used in different Spring Cloud implementations (such

as Spring Cloud Netflix and Spring Cloud Consul).

If you get an exception due to "Illegal key size" and you use Sun’s JDK, you need to install the Java Cryptography Extension (JCE) Unlimited Strength Jurisdiction Policy Files. See the following links for more information:

 Java 6 JCE

 Java 7 JCE

 Java 8 JCE

Extract the files into the JDK/jre/lib/security folder for whichever version of JRE/JDK x64/x86 you use.

2. Spring Cloud Context: Application Context Services

Spring Boot has an opinionated view of how to build an application with Spring. For instance, it has conventional locations for common configuration files and has endpoints for common management and monitoring tasks. Spring Cloud builds on top of that and adds a few features that probably all components in a system would use or occasionally need.

2.1 The Bootstrap Application Context

A Spring Cloud application operates by creating a “bootstrap” context, which is a parent context for the main application. It is responsible for loading configuration properties from the external sources and for decrypting properties in the local external configuration files. The two contexts share an Environment , which is the source of external properties for any Spring application. By default, bootstrap properties (not bootstrap.properties but properties that are loaded during the bootstrap phase) are added with high precedence, so they cannot be overridden by local configuration.The bootstrap context uses a different convention for locating external configuration than the main application context. Instead of application.yml (or .properties ), you can use bootstrap.yml , keeping the external configuration for bootstrap and main context

nicely separate. The following listing shows an example:

bootstrap.yml.

spring:
 application:
 name: foo
 cloud:
 config:
 uri: ${SPRING_CONFIG_URI:http://localhost:8888}

If your application needs any application-specific configuration from the server, it is a good idea to set the spring.application.name (in bootstrap.yml or application.yml ).You can disable the bootstrap process completely by setting spring.cloud.bootstrap.enabled=false (for example, in system properties).

2.2 Application Context Hierarchies

If you build an application context from SpringApplication or SpringApplicationBuilder , then the Bootstrap context is added as a parent to that context. It is a feature of Spring that child contexts inherit property sources and profiles from their parent, so the “main” application context

contains additional property sources, compared to building the same context without Spring Cloud Config. The additional property sources are:

 “bootstrap”: If any PropertySourceLocators are found in the Bootstrap context and if they have non-empty properties, an optional CompositePropertySourceappears with high priority. An example would be properties from the Spring Cloud Config Server. See “Section 2.6, “Customizing the Bootstrap Property Sources”” for instructions on how to customize the contents of this property source.

 “applicationConfig: [classpath:bootstrap.yml]” (and related files if Spring profiles are active): If you have a bootstrap.yml (or .properties ), those properties are used to configure the Bootstrap context. Then they get added to the child context when its parent is set. They have lower precedence than the application.yml (or .properties ) and any other property sources that are added to the child as a normal part of the process of creating a Spring Boot application. See “Section 2.3, “Changing the Location of Bootstrap Properties”” for instructions on how to customize the contents of these property sources.

Because of the ordering rules of property sources, the “bootstrap” entries take precedence. However, note that these do not contain any data from bootstrap.yml , which has very low precedence but can be used to set defaults.You can extend the context hierarchy by setting the parent context of any ApplicationContext you create — for example, by using its own interface or with the SpringApplicationBuilder convenience methods ( parent() , child() and sibling() ). The bootstrap context is the parent of the most senior ancestor that you create yourself. Every context in the hierarchy has its own “bootstrap” (possibly empty) property source to avoid promoting values inadvertently from parents down to their descendants. If there is a Config Server, every context in the hierarchy can also (in principle) have a different spring.application.name and, hence, a different remote property source. Normal Spring application context behavior rules apply to property resolution: properties from a child context override those in the parent, by name and also by property source name. (If the child has a property source with the same name as the parent, the value from the parent is not included in the child).Note that the SpringApplicationBuilder lets you share an Environment amongst the whole hierarchy, but that is not the default. Thus, sibling contexts, in particular, do not need to have the same profiles or property sources, even though they may share common values with their parent.

2.3 Changing the Location of Bootstrap Properties

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