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In many ways, the Spring Framework's extremely flexible ability to integrate with other powerful frameworks makes it ideal for building clusters of microservices, especially using Spring Boot and Spring Cloud. However, new developers often find Spring Framework hard to grasp and exceedingly complex, partly due to the number of configurations needed to run applications.
Let's take a look at Spring Boot and Spring Cloud, including how they can be used effectively to build microservices and how to take on complex configuration issues.
What is Spring?
The Spring Framework offers a comprehensive programming and configuration model for use on any deployment platform. IT teams can use the framework's rich set of portfolio projects and Java-based lifecycle management tools to free up resources and focus on application-level logic. In addition, developers can quickly build next-generation applications that are scalable, portable and easy to update.
As the de-facto framework for web applications, the Spring Framework includes a massive number of library integrations and offers its own dependency injection (DI) and inversion of control (IoC) features. Developers can use DI and IoC to build loosely coupled applications that are easier to scale and to unit test. Developers can access interfaces such as Dispatcher Servlet, ModelAndView and ViewResolver to decouple application objects and further simplify development.
Building microservices with Spring Boot
The Spring Boot framework module makes it simple to create stand-alone applications that can run immediately as self-contained deployment units. Moreover, developers can create various configuration profiles in Spring for different environments and easily segregate parts of their application configuration. In addition, Spring Boot provides starter dependency descriptors that alleviate the need to hunt through sample code and find these descriptors.
Spring Boot automatically configures Spring and third-party libraries throughout the course of a build. It also provides related features, including the ability to build patterns common to distributed systems, embed Tomcat, Jetty and Undertow directly into deployments and add production-ready features such as health checks and metrics.
Deploying Spring Boot's configuration service
Developers can quickly deploy their applications using Spring Boot's minimal upfront configuration. In general, you should store configurations for microservice applications in the environment and not in the project. Spring Boot handles the configurations for all of the services through a point-to-point service call that retrieves those configurations. Using its built-in auto-configuration feature, the framework will automatically apply all the internal dependencies that your application requires.
One possible pitfall with Spring Boot is an increase in the deployment binary size due to unused dependencies. However, since the configurations are both in one external and central place, developers can organize version controls and perform revisions without the need to restart a service for a configuration change.
In addition, Spring Boot's Discovery Service feature maintains a list of the service instances available for work within a cluster. Once the developer identifies the service for contact and provides the service's ID, Spring autowires all mappings and identifications. Spring Boot's API gateway feature works the same way and will automatically reroute API requests to the service instances that own the route being requested through HTTP.
But remember that while Spring Boot's automation features simplify development, it is challenging to convert existing or legacy Spring Framework projects into Spring Boot. Developers cannot deploy multiple web apps in the same process, which means they can't share managed resources such as connection pools. Not to mention, the sheer number of library integrations clearly outnumber competing frameworks.
Creating applications with Spring Cloud
Spring Cloud builds on the concepts of Spring Boot to solve some of the problems that developers encounter when building microservices. Spring Cloud incorporates both Spring Framework's unified programming model and Spring Boot's rapid application development capabilities. It also improves and builds on top of open source cloud offerings like Netflix OSS.
Spring Cloud essentially provides a variety of design patterns to follow when building cloud-native applications. For example, you can access Spring Cloud modules to address a number of distributed application concerns. Furthermore, Spring Cloud provides Eureka-based service registry and discovery support to alleviate the need for hard-coded hostnames and port numbers.
The framework also provides distributed tracing for debugging issues, single sign-on for increased security and API development agreements through Spring Cloud contracts. Through this, developers gain the ability to fine-tune applications using Spring Cloud's rich set of Java-based libraries. Each of these libraries covers various runtime issues that can occur when building distributed systems for cloud services.
On the downside, Spring Cloud needs Java. Another limitation is Spring's inability to interchange technology stacks, libraries and languages. Moreover, a developer must make sure the Spring Cloud Config Server is up and running every time in order to run a single microservice. These build and runtime dependencies mean that developers must devise ways to make the Config Server highly available.
Spring Boot and Spring Cloud: A powerful combination
Ultimately, Spring Boot and Spring Cloud provide considerable benefits for Java-based developers tasked with building microservices. They provide great flexibility and control, extensive library integrations and effective auto configuration. Part of the power of Spring Boot rests on the wide array of starter dependencies, which significantly increase developer productivity. Similarly, Spring Cloud modules can ensure resilience, reliability and coordination of cloud-based microservices.