In Chapter 4, Evolution toward Microservices and Cloud-Native Applications, we discussed the problems with monolithic applications and how architectures evolved toward microservices. However, microservices have their own sets of challenges:

• Organizations adopting microservice architectures also need to make challenging decisions around the consistency of microservices without affecting the innovation capabilities of the microservice teams.
• Smaller applications mean more builds, releases, and deployments. This is usually addressed using more automation.
• Microservice architectures are built based on a large number of smaller, fine-grained services. There are challenges associated with managing configuration and availability of these services.
• Debugging issues becomes more difficult because of the distributed nature of applications.

To reap maximum benefits from microservice architectures, microservices should be Cloud-Native--easily deployable on the Cloud. In Chapter 4, Evolution toward Microservices and Cloud-Native Applications, we discussed the characteristics of Twelve-Factor Apps--patterns that are typically considered good practices in Cloud-Native applications.

Spring Cloud aims to provide solutions to some commonly encountered patterns when building systems on the Cloud. Some of the important features include the following:

• Solutions to manage distributed microservice configuration
• Service registration and discovery using Name servers
• Load balancing across multiple instances of microservices
• More fault-tolerant services using circuit breakers
• API Gateways for aggregation, routing, and caching
• Distributed tracing across microservices

It is important to understand that Spring Cloud is not a single project. It is a group of subprojects aimed at solving the problems associated with applications deployed on the Cloud.

Some important Spring Cloud subprojects are as follows:

• Spring Cloud Config: Enables centralized external configuration across different microservices across different environments.
• Spring Cloud Netflix: Netflix is one of the early adopters of microservice architecture. A number of internal Netflix projects were open sourced under the umbrella of Spring Cloud Netflix. Examples include Eureka, Hystrix, and Zuul.
• Spring Cloud Bus: Makes it easier to build the integration of microservices with a lightweight message broker.
• Spring Cloud Sleuth: Along with Zipkin, this provides distributed tracing solutions.
• Spring Cloud Data Flow: Provides capabilities for building orchestration around microservice applications. Provides a DSL, GUI, and REST API.
• Spring Cloud Stream: Provides a simple declarative framework to integrate Spring-based (and Spring Boot)-based applications with message brokers such as Apache Kafka or RabbitMQ.

A few things are common to all projects under the Spring Cloud umbrella:

• They solve some of the common problems with developing applications on the Cloud
• They provide great integration with Spring Boot
• They are typically configured with simple annotations
• They make extensive use of auto-configuration