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Chris Rogers
Chris Rogers

Microservices Patterns: With Examples In Java LINK


The goal of this architecture is to decouple the front-end apps from the backend architecture.As a scenario, think about you have an application that consists of the mobile app, web app and needs to communicate with the backend services in a microservices architecture.




Microservices Patterns: With examples in Java



One challenge with using the microservice operation is implementing distributed operations, which span multiple services.This is especially challenging since each service has its own database.The solution is to use the service collaboration patterns:


Microservice architecture has become the de facto choice for modern application development. Though it solves certain problems, it is not a silver bullet. It has several drawbacks and when using this architecture, there are numerous issues that must be addressed. This brings about the need to learn common patterns in these problems and solve them with reusable solutions. Thus, design patterns for microservices need to be discussed. Before we dive into the design patterns, we need to understand on what principles microservice architecture has been built:


With microservices, the UI has to be designed as a skeleton with multiple sections/regions of the screen/page. Each section will make a call to an individual backend microservice to pull the data. That is called composing UI components specific to service. Frameworks like AngularJS and ReactJS help to do that easily. These screens are known as Single Page Applications (SPA). This enables the app to refresh a particular region of the screen instead of the whole page.


We have talked about one database per service being ideal for microservices, but that is possible when the application is greenfield and to be developed with DDD. But if the application is a monolith and trying to break into microservices, denormalization is not that easy. What is the suitable architecture in that case?


A shared database per service is not ideal, but that is the working solution for the above scenario. Most people consider this an anti-pattern for microservices, but for brownfield applications, this is a good start to break the application into smaller logical pieces. This should not be applied for greenfield applications. In this pattern, one database can be aligned with more than one microservice, but it has to be restricted to 2-3 maximum, otherwise scaling, autonomy, and independence will be challenging to execute.


There are many other patterns used with microservice architecture, like Sidecar, Chained Microservice, Branch Microservice, Event Sourcing Pattern, Continuous Delivery Patterns, and more. The list keeps growing as we get more experience with microservices. I am stopping now to hear back from you on what microservice patterns you are using.


I first became familiar with Chris Richardson through his online resource, Microservices.io. Which, to be honest, provides an overwhelming amount of information - information that I've deferred consuming because I didn't really know how to approach it; especially with my lack of microservices experience. I'm more of a book person. So, when I heard that Chris was coming out with a book, Microservices Patterns: With Examples In Java, I was thrilled. So thrilled, in fact, that I couldn't wait for it be published. Instead, I purchased it through Manning's Early Access Program (MEAP). I've spent the last week reading through it and I've found it to be a fascinating, pragmatic, and holistic exploration of microservices development.


The whole book follows Mary - the CTO of Food To Go, Inc (FTGO) - as she attempts to grow her business by refactoring her old monolithic application into a microservices architecture. She's doing this because her development velocity has dropped and upper management is becoming increasingly frustrated with the engineers' inability to ship new features with sufficiently-high quality.


As organizations shift from monolithic applications to smaller, self-contained microservices, distributed systems have become more fine-grained. But developing these new systems brings its own host of problems. This expanded second edition takes a holistic view of topics that you need to consider when building, managing, and scaling microservices architectures. Through clear examples and practical advice, author Sam Newman gives everyone from architects and developers to testers and IT operators a firm grounding in the concepts.


Developing your application as a modular monolith might seem like a hack or going backward in architectural evolution, but I have seen it work fine in practice. It is not a microservices pattern but an exception to the microservices rule that can be combined cautiously with microservices. When strong write consistency is the driving requirement, more important even than the ability to deploy and scale microservices independently, then you could go with the modular monolith architecture.


Having a monolithic architecture does not imply that the system is poorly designed or bad. It does not say anything about quality. As the name suggests, it is a system designed in a modular way with exactly one deployment unit. Note that this is a purposefully designed and implemented modular monolith, which is different from an accidentally created monolith that grows over time. In a purposeful modular monolith architecture, every module follows the microservices principles. Each module encapsulates all the access to its data, but the operations are exposed and consumed as in-memory method calls.


With this approach, you have to convert both microservices (Service A and Service B) into library modules that can be deployed into a shared runtime. You then make both microservices share the same database instance. Because the services are written and deployed as libraries in a common runtime, they can participate in the same transactions. Because the modules share a database instance, you can use a local transaction to commit or rollback all changes at once. There are also differences around the deployment method because we want the modules to be deployed as libraries within a bigger deployment, and to participate in existing transactions.


The last piece of the puzzle is to use a runtime and a wrapper service capable of consuming other modules and including them in the context of an existing transaction. All of these constraints make the modules more tightly coupled than typical microservices, but the benefit is that the wrapper service can start a transaction, invoke the library modules to update their databases, and commit or roll back the transaction as one operation, without concerns about partial failure or eventual consistency.


If you are going further left in the spectrum, most likely you have a very strong need for data consistency and you are ready to pay for it with significant tradeoffs. In this case, distributed transactions through two-phase commits will work with certain data sources, but they are difficult to implement reliably on dynamic cloud environments designed for scalability and high availability. In that case, you can go all the way to the good old modular monolith approach, accompanied by practices learned from the microservices movement. This approach ensures the highest data consistency but at the price of runtime and data source coupling.


Despite the title full title in a somewhat misleading way says with examples in Java there were very few actually code examples and if they were they may as well have been in pseudo code because they were really easy to understand. There were the mentions to Java Frameworks like spring etc, but the features mentioned are also present in other frameworks that I am familiar with.


In this hands-on, example-driven guide, Java developers and architects will learn how to navigate popular application frameworks, such as Dropwizard and Spring Boot, and how to deploy and manage microservices at scale with Linux containers.


This book walks you through a detailed comparison of microservices and SOA, by learning the core differences between the two with regard to architecture style and characteristics, service characteristics, and capability.


Walks through the 10 most common microservices anti-patterns and pitfalls, and provides solutions for avoiding them: how to avert the most flagrant anti-patterns and pitfalls before you tussle with microservice granularity, data migration, distributed processing.


Martin Fowler is an author, speaker, and general loud-mouth on software development. He's long been puzzled by the problem of how to componentize software systems, having heard more vague claims than he's happy with. He hopes that microservices will live up to the early promise its advocates have found.


We cannot say there is a formal definition of the microservices architectural style, but we can attempt to describe what we see as common characteristics for architectures that fit the label. As with any definition that outlines common characteristics, not all microservice architectures have all the characteristics, but we do expect that most microservice architectures exhibit most characteristics. While we authors have been active members of this rather loose community, our intention is to attempt a description of what we see in our own work and in similar efforts by teams we know of. In particular we are not laying down some definition to conform to. 041b061a72


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