Whether you are a beginner or an experienced or trying to become a developer in the near future, you must have at least heard about the term Microservices. Undoubtedly, if you are working on it, you must have already had a good experience with it. Moreover, you must also have observed that the term ‘Spring Cloud’ comes in between while talking about Microservices. Do you know, why so? If you know it’s good. If not, let’s spare some time going through this article thoroughly.
In this article, apart from knowing what is Spring Cloud, you will also get to know what are the features, capabilities and other fundamental concepts of Spring Cloud that are expected from a Microservices developer. Let’s start discussing the topic ‘Spring Cloud Essentials’.
What is Spring Cloud?
While developing an application in a distributed environment, we come across various common patterns, such as Service Registry & Discovery, Configuration management, circuit breakers, distributed sessions, global locks, leadership election, cluster state etc. Spring Cloud offers developers a range of tools that enable the rapid development of these common patterns in distributed systems.
Coordinating distributed systems results in boilerplate patterns. By using Spring Cloud, developers can quickly create services and applications that implement these patterns. These services will function well in any distributed environment, including the developer’s own laptop, on-premise data centers, and managed platforms like Cloud Foundry.
In simple words, Spring Cloud is an open-source framework that builds on top of the well-known Spring Boot to empower the smooth development of cloud-native applications. It addresses common challenges associated with distributed systems, such as configuration management, service discovery, load balancing, fault tolerance, and more. By utilizing Spring Cloud, developers can focus on building application features without worrying about the difficulties of distributed environments.
What are the features of Spring Cloud?
Spring Cloud is intended to offer a built-in and user-friendly experience for common use cases. Apart from that, it is also offering a scalable mechanism to accommodate specific requirements and use cases beyond the standard ones. here are some of the important features of it:
- Distributed/versioned configuration
- Service registration and discovery
- Service-to-service calls
- Load balancing
- Circuit Breakers
- Global locks
- Leadership election and cluster state
- Distributed messaging
In Spring Cloud, distributed/versioned configuration refers to the ability of managing application configurations in a distributed manner while maintaining version control. It permits developers to store and retrieve configuration settings for microservices and other components of a distributed system from a centralized configuration server.
With distributed/versioned configuration, developers can easily make changes to the configuration properties without modifying the application code. The configuration server acts as a single central place for configuration settings, allowing faultless updates and ensuring that all instances of the microservices access the latest configuration. The configuration server is generally called Spring Cloud Config Server.
By separating the configuration from the application code, developers can update configuration settings on-the-fly, making it easier to adjust to dynamic environments and respond quickly to changing requirements. Additionally, having versioned configurations allows developers to track changes and roll back to previous versions if needed, ensuring better control and monitoring of the configuration changes.
Service Registration and Discovery
It refers to the process of registering each microservices with a centralized registry and allowing other services to discover and communicate with them dynamically when required. Service Registration and Discovery enables services to independently register themselves with a service registry when they start up. The service registry acts as a centralized repository that keeps track of all the available services and their locations.
When a service needs to communicate with another service, it no longer requires hardcoded IP addresses or URLs. Instead, it queries the service registry to discover the location of the desired service. This dynamic discovery ensures that services can interact with each other seamlessly, regardless of changes in their locations or the addition/removal of service instances.
Spring Cloud offers an effective and lightweight service discovery tool called Eureka, which simplifies the implementation of Service Registration and Discovery. For complete example, kindly visit a separate article on ‘How to register & discover Microservices using Netflix Eureka?‘
In Spring Cloud, routing refers to the process of wisely directing incoming requests to the appropriate microservice instances based on specific rules or conditions. Routing is essential in a distributed system where multiple instances of a microservice may be running to handle high traffic and ensure high availability. By using routing mechanisms, Spring Cloud enables developers to efficiently manage incoming requests, distribute the load consistently across available instances.
For this purpose, Spring Cloud Gateway is a starter project provided by Spring Cloud. Spring Cloud Gateway works on the Netty server provided by Spring Boot and Spring Webflux. It does not work in a traditional Servlet Container like Tomcat. Therefore, when we start a Spring Boot Gateway application, it automatically starts with Netty server.
Service-to-service calls in Spring Cloud refer to the communication between different microservices within a distributed system. In a microservices architecture, individual services often need to interact with each other to fulfill specific business functionalities or exchange data.
Spring Cloud provides mechanisms to simplify these service-to-service calls, permitting faultless and efficient communication between microservices. One of the common approaches to achieving service-to-service communication in Spring Cloud is through the use of RESTful APIs. Spring Cloud offers Feign client as one of the popular API for this purpose.
Load balancing is always a primary requirement in distributed systems where multiple instances of a service may be running to handle high traffic and provide fault tolerance. It helps streamline the consumption of resources and boosts the overall performance and scalability of microservices architectures. When a client makes a request to a microservice, the load balancer intelligently selects one of the available instances of that service to handle the request.
Spring Cloud powers a client-side load balancing library called Open Feign to implement load balancing. Open Feign works in conjunction with a service registry, such as Eureka, to discover available instances of a microservice. It then applies predefined load balancing algorithms to distribute the incoming requests among the available instances.
The load balancer continuously monitors the health and responsiveness of each service instance. If an instance becomes inaccessible or unresponsive, the load balancer automatically redirects the requests to other healthy instances. Hence, it helps promote fault tolerance and high availability.
In Spring Cloud, a circuit breaker is an effective pattern used to strengthen the resilience and fault tolerance of microservices in a distributed system. It is intended to avoid cascading failures and maintain the overall stability of the application, primarily when dependent services experience issues or become unresponsive.
When a microservice makes a request to another service, the circuit breaker monitors the response. If the response times out or indicates a failure, the circuit breaker immediately opens, similar to a physical circuit breaker. Once the circuit is open, subsequent requests to the troubled service are not allowed to go through. Instead, the circuit breaker provides a fallback response or error message, indicating that the service is unavailable.
Moreover, circuit breakers can automatically attempt to close the circuit after a specified period, allowing the microservice to check if the dependent service has recovered. If the subsequent requests succeed, the circuit is closed again, and the microservice resumes normal operations. However, if the dependent service continues to be unresponsive, the circuit breaker remains open, saving resources and preventing further impact on the system.
Spring Cloud integrates with the Resilience4j library to implement circuit breakers effectively. Resilience4j provides an easy-to-use and configurable solution to handle the circuit breaker pattern, making it a reliable tool for building resilient microservices architectures in distributed systems. Moreover, Resilience4j provides other modules, such as Rate Limiting, Bulkheading, Automatic Retrying, Timeout Handling, and Result Caching.
Global locks refer to a synchronization mechanism that allows multiple processes or microservices in a distributed system to coordinate their actions and ensure mutually exclusive access to a shared resource. In a distributed environment, it is essential to prevent multiple services from accessing or modifying a shared resource simultaneously, as it can lead to data corruption, race conditions, and other concurrency-related issues.
For example, if multiple microservices need to perform an operation that involves updating a shared database record, they can use global locks to coordinate their actions. When a microservice wants to modify the shared record, it tries to acquire the lock. If the lock is already held by another microservice, the requesting microservice will wait until the lock is released. Once the first microservice completes its operation and releases the lock, the next microservice in line can acquire the lock and proceed with its operation.
Using global locks in a distributed system can help prevent race conditions and ensure data integrity when multiple services need to access shared resources concurrently.
Leadership Election and Cluster State
Leadership Election is the process by which one instance or node within a distributed system is designated as the “leader” responsible for coordinating and managing certain tasks or operations. The leader node takes on additional responsibilities and acts as a central point of authority within the system.
Leadership Election is crucial in scenarios where multiple instances of a service or microservice are running simultaneously, and only one instance should be responsible for performing certain actions or making critical decisions. Examples of such scenarios include task scheduling, data consistency, or coordination of distributed services.
Spring Cloud provides tools and libraries that support Leadership Election in a distributed environment. For example, Apache ZooKeeper and Apache Curator offer election algorithms that allow instances to compete for leadership and elect a single leader based on configurable criteria. Once a leader is elected, it holds the leadership position until it steps down or becomes unavailable, at which point a new election may occur to select a new leader.
Cluster State management involves maintaining and propagating information about the health, availability, and status of all instances or nodes within a distributed system. It enables instances to be aware of the current state of the cluster, including the presence of new nodes, changes in node status, and the availability of services.
In a dynamic and distributed environment, instances of services may join or leave the cluster based on scaling needs or system failures. Cluster State management ensures that all instances are informed of these changes and can adapt their behavior accordingly.
Spring Cloud offers integrations with service discovery tools like Eureka and Consul, which help maintain the Cluster State. These tools provide a centralized registry that keeps track of available instances and their metadata, such as IP addresses, ports, and health status. When an instance joins or leaves the cluster, it registers or de-registers itself with the service registry, allowing other instances to be informed about the changes and adjust their communication accordingly.
Distributed Messaging in Spring Cloud is a communication pattern and mechanism that enables faultless exchange of data and messages among various components and microservices within a distributed system.
In a microservices architecture, individual services need to interact and exchange information with each other to satisfy business functionalities. Distributed Messaging provides a way for microservices to communicate asynchronously, meaning services can send and receive messages without needing immediate responses. This decouples the sender and receiver, allowing them to operate independently and asynchronously.
With Distributed Messaging, microservices can publish events or messages to a message broker, and other services can subscribe to these events and react accordingly. This event-driven communication style enables services to respond to changes or events in real-time and allows for better handling of asynchronous workflows.
Spring Cloud offers various tools and libraries to implement Distributed Messaging. One of the popular solutions is Spring Cloud Stream, which provides abstractions for messaging middleware like Apache Kafka, RabbitMQ, and others. It allows developers to easily integrate with different messaging systems without being tightly coupled to any specific technology.
What are the primary projects under Spring Cloud Essentials to develop Spring Boot Microservices?
Below is the list of primary projects that are required to develop Spring Boot Microservices:
- Spring Cloud Netflix
- Spring Cloud OpenFeign
- Spring Cloud Config
- Spring Cloud Gateway
- Spring Cloud Circuit Breaker
- Spring Cloud Sleuth
- Spring Cloud Stream
- Spring Cloud Zookeeper
In order to have a clear understanding of the aforementioned projects, you may visit a separate article on Microservices In Java.
Q#1. What is the prerequisite to work on Spring Cloud?
Before learning Spring Cloud, you must have the fundamental understanding of Spring and Spring Boot Framework.
Q#2. What is Spring Cloud vs. Spring Boot?
Although Spring Cloud and Spring Boot are two supplementary frameworks in the Spring ecosystem, but they serve different purposes and address different problems in the development of applications.
Spring Boot focuses on simplifying the application setup and reducing boilerplate code, making it easier for developers to create Spring-based applications quickly. On the other hand, Spring Cloud is a set of tools and libraries that build on top of Spring Boot to address challenges faced in building Microservices based applications. In simple words, Spring Cloud extends the capabilities of Spring Boot to provide the essential features for building robust and scalable Microservices based applications in a distributed environment.
Q#3. When should I use Spring Cloud?
You should consider using Spring Cloud when you are building a distributed system or a Microservices based application. Spring Cloud is specifically designed to address the challenges and complexities that arise in such environments. Here are some scenarios where Spring Cloud can be beneficial:
1) Microservices Architecture: If you are adopting a Microservices architecture, where you break down your application into small, independent services, Spring Cloud provides essential tools for service discovery, load balancing, routing, and communication between Microservices.
2) Cloud-Native Applications: When developing cloud-native applications that can dynamically scale, handle failures gracefully, and adapt to a dynamic environment, Spring Cloud’s features for service discovery, circuit breakers, and distributed configuration management become invaluable.
3) Resilient Communication: If you need to implement resilient communication patterns like circuit breakers, retries, and fallbacks to ensure that your services can handle failures and maintain overall system stability, Spring Cloud offers built-in support for such patterns.
4) Distributed Configuration: When you require a centralized configuration management solution to manage configuration settings for multiple Microservices across different environments, Spring Cloud Config provides a simple and effective solution.
5) Service Discovery and Load Balancing: If you need a way for your services to dynamically discover and communicate with each other, Spring Cloud’s integration with service discovery tools like Eureka and load balancing libraries like Ribbon simplifies this process.
6) Distributed Tracing: When you want to trace and monitor the interactions between Microservices to diagnose performance issues, debug problems, and optimize the overall system, Spring Cloud Sleuth provides distributed tracing capabilities.
7) Event-Driven Applications: If you are building event-driven applications that require asynchronous communication using messaging systems like Kafka or RabbitMQ, Spring Cloud Stream offers abstractions to easily implement such event-driven workflows.
Q#4. Is Spring Cloud and Microservices same?
Microservices is an architecture where you break down your application into small and independent services. On the other hand, Spring Cloud is a set of essential tools and libraries provided by the Spring Boot ecosystem to develop Microservices based applications.
Microservices is an architectural style, while Spring Cloud is a toolkit that supports the development of Microservices-based applications in the Java ecosystem, especially using Spring Boot. Spring Cloud is an implementation of various Microservices-related patterns and best practices that integrate well with the Spring framework, making it easier for developers to build and manage Microservices-based applications.