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Microservices with Clojure
Microservices with Clojure

Microservices with Clojure: Develop event-driven, scalable, and reactive microservices with real-time monitoring

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Microservices with Clojure

Microservices Architecture

"Gather together the things that change for the same reasons. Separate those things that change for different reasons."

- Robert Martin, Single Responsibility Principle

Software architecture plays a key role in identifying the behavior of the system before it is built. A well-designed software architecture leads to flexible, reusable, and scalable components that can be easily extended, verified, and maintained over time. Such architectures evolve over time and help pave the way for the adoption of next-generation architectures. For example, a well-designed monolithic application that is built on the principles of Separation of Concern (SoC) is easier to migrate to microservices than an application that does not have well-defined components. In this chapter, you will:

  • Learn a systematic approach to designing microservices using...

Domain-driven design

Ideal enterprise systems are tightly integrated and provide all business capabilities as a single unit that is optimized for a particular technology stack and hardware. Such monolithic systems often grow so complex over time that it becomes challenging to comprehend them as a single unit by a single team. Domain-driven design advocates disintegrating such systems into smaller modular components and assigning them to teams that focus on a single business capability in a bounded context (https://en.wikipedia.org/wiki/Domain-driven_design#Bounded_context). Once disintegrated, all such components are made a part of an automated continuous integration (CI) process to avoid any fragmentation. Since these components are built in isolation and often have their own data models and schema, there should be a well-defined contract to interact with the components...

Components

Once the bounded contexts are identified for microservices and the organization structure is aligned, each microservice must be considered as a product that is tested, deployed, and scaled in isolation by the same team that developed it. A well-designed microservice must never expose its internal data model to the outside world directly. Instead, it must maintain a service contract that maps to its internal model such that it can evolve over time without affecting the dependent microservices.

Component-based software engineering (https://en.wikipedia.org/wiki/Component-based_software_engineering) defines a component as a reusable module that is based on the principles of SoC and encapsulates a set of related functions and data. In the context of microservices architecture, it is recommended to implement each service as a component that is independently swappable...

Messaging and contracts

In monolithic applications, messaging between components is mostly achieved using function calls, whereas for microservices, it is achieved using lightweight messaging systems, often HTTP(S). Using a lightweight messaging system is one of the most promising features of microservices and makes it easier to adopt and scale, as compared to service-oriented architecture (SOA) that uses a complex messaging system with multiple protocols. Microservices are more about keeping the endpoints smart and the communication channels as simple as possible.

In a microservices architecture, often multiple microservices need to interact with each other to achieve a particular task. These interactions can be either direct, via request-response-based (https://en.wikipedia.org/wiki/Request-response) communication, or through a lightweight message-oriented middleware (MOM...

Service discovery

All the APIs exposed by a microservice are accessible via the IP address and port of the host machine on which the microservice is deployed. Since microservices are deployed in a virtual machine or a container that has a dynamic IP, it is quite possible that the IPs and ports that are allocated to the microservice APIs may change over time. Therefore, IP addresses and ports of services should never be hardcoded by the depending microservice. Instead, there should be a common database of all the services that are active for the current application. Such a database of services is called the service registry in microservices architecture and is always kept up to date with the location of the microservices. It keeps the details of all the active microservices including their current IP address and port. Microservices then query this service...

Data management

In a microservices-based architecture, the data model and schema must not be shared among bounded contexts. Each microservice must implement its own data model backed by a database that is accessible only through the service endpoints. Microservices may also publish events that can be considered as a log of the changes the service applies to its isolated database. Keeping application data up to date across microservices may also add to the network overhead and data duplication.

Direct lookup

Although microservices have their own isolated persistence, an application implemented using microservices may need to share data among a set of services to perform tasks. In a monolithic environment, since there is...

Automated continuous deployment

The core philosophy of a microservice environment must be based on the You build it, you run it (https://queue.acm.org/detail.cfm?id=1142065) model; that is, the team working on the microservice must own it end to end, right from development to deployment. The infrastructure required for the team to integrate, test, and deploy any changes must be completely automated. This makes it possible to build a continuous integration and continuous delivery (CD) pipeline, which is the backbone of microservices-based architectures.

CI/CD

The term CI/CD combines the practices of CI and CD together as a seamless process. In a typical microservices-based setup, the team continuously works on...

Summary

In this chapter, we learned about domain-driven design and the importance of identifying the right bounded context for microservices. We learned about the hexagonal architecture for microservices and various messaging patterns. We also discussed data management patterns for microservices and how to set up service registries to discover microservices. We concluded with the importance of automating the entire microservice deployment cycle including testing, deployment, and scaling. In the next chapter, we will introduce a real-life use case for microservices and learn how to design an application using the concepts learned in this chapter.

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Key benefits

  • Relevance of the microservice architecture and benefits of Clojure's functional and simple features to implement it.
  • Learn best practices and common principles to avoid common pitfalls while developing microservices.
  • Learn how to use Pedestal to build your next microservices, secure them using JWT, and monitor them using the ELK stack

Description

The microservice architecture is sweeping the world as the de facto pattern with which to design and build scalable, easy-tomaintain web applications. This book will teach you common patterns and practices, and will show you how to apply these using the Clojure programming language. This book will teach you the fundamental concepts of architectural design and RESTful communication, and show you patterns that provide manageable code that is supportable in development and at scale in production. We will provide you with examples of how to put these concepts and patterns into practice with Clojure. This book will explain and illustrate, with practical examples, how teams of all sizes can start solving problems with microservices. You will learn the importance of writing code that is asynchronous and non-blocking and how Pedestal helps us do this. Later, the book explains how to build Reactive microservices in Clojure that adhere to the principles underlying the Reactive Manifesto. We finish off by showing you various ways to monitor, test, and secure your microservices. By the end, you will be fully capable of setting up, modifying, and deploying a microservice with Clojure and Pedestal.

Who is this book for?

You should have a working knowledge of programming in Clojure. However, no knowledge of RESTful architecture, microservices, or web services is expected. If you are looking to apply techniques to your own projects, taking your first steps into microservice architecture, this book is for you.

What you will learn

  • Explore the pros and cons of monolithic and microservice architectures
  • Use Clojure to effectively build a reallife application using Microservices
  • Gain practical knowledge of the Clojure Pedestal framework and how to use it to build Microservices
  • Explore various persistence patterns and learn how to use Apache Kafka to build event-driven microservice architectures
  • Secure your Microservices using JWT
  • Monitor Microservices at scale using the ELK stack
  • Deploy Microservices at scale using container orchestration platforms such as Kubernetes
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Table of Contents

12 Chapters
Monolithic Versus Microservices Chevron down icon Chevron up icon
Microservices Architecture Chevron down icon Chevron up icon
Microservices for Helping Hands Application Chevron down icon Chevron up icon
Development Environment Chevron down icon Chevron up icon
REST APIs for Microservices Chevron down icon Chevron up icon
Introduction to Pedestal Chevron down icon Chevron up icon
Achieving Immutability with Datomic Chevron down icon Chevron up icon
Building Microservices for Helping Hands Chevron down icon Chevron up icon
Configuring Microservices Chevron down icon Chevron up icon
Event-Driven Patterns for Microservices Chevron down icon Chevron up icon
Deploying and Monitoring Secured Microservices Chevron down icon Chevron up icon
Other Books You May Enjoy Chevron down icon Chevron up icon

Customer reviews

Rating distribution
Full star icon Full star icon Full star icon Full star icon Half star icon 4.5
(2 Ratings)
5 star 50%
4 star 50%
3 star 0%
2 star 0%
1 star 0%
Felipe Caetano Silva May 16, 2020
Full star icon Full star icon Full star icon Full star icon Full star icon 5
Com relação ao Produto em si, achei o acabamento do livro um pouco a desejar. O Conteúdo é o que eu esperava interessante, um bom introdutório aos microserviços e a clojure.
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Amazon Customer Sep 03, 2020
Full star icon Full star icon Full star icon Full star icon Empty star icon 4
Microservices with Clojure is really great for learning to put together more serious applications and especially for going into depth on using Pedestal for web services.
Amazon Verified review Amazon
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