Book Image

The Definitive Guide to Modernizing Applications on Google Cloud

By : Steve (Satish) Sangapu, Dheeraj Panyam, Jason Marston
Book Image

The Definitive Guide to Modernizing Applications on Google Cloud

By: Steve (Satish) Sangapu, Dheeraj Panyam, Jason Marston

Overview of this book

Legacy applications, which comprise 75–80% of all enterprise applications, often end up being stuck in data centers. Modernizing these applications to make them cloud-native enables them to scale in a cloud environment without taking months or years to start seeing the benefits. This book will help software developers and solutions architects to modernize their applications on Google Cloud and transform them into cloud-native applications. This book helps you to build on your existing knowledge of enterprise application development and takes you on a journey through the six Rs: rehosting, replatforming, rearchitecting, repurchasing, retiring, and retaining. You'll learn how to modernize a legacy enterprise application on Google Cloud and build on existing assets and skills effectively. Taking an iterative and incremental approach to modernization, the book introduces the main services in Google Cloud in an easy-to-understand way that can be applied immediately to an application. By the end of this Google Cloud book, you'll have learned how to modernize a legacy enterprise application by exploring various interim architectures and tooling to develop a cloud-native microservices-based application.
Table of Contents (26 chapters)
1
Section 1: Cloud-Native Application Development and App Modernization in Google Cloud
5
Section 2: Selecting the Right Google Cloud Services
10
Section 3: Rehosting and Replatforming the Application
17
Section 4: Refactoring the Application on Cloud-Native/PaaS and Serverless in Google Cloud

The compensation pattern

Using our example of an Order and a Stock microservice from the previous section, we will now look at what happens if we have no stock to allocate for the order. These two microservices are decoupled, so do not share a traditional transaction boundary. We need a mechanism for the Stock microservice to inform the Order microservice that it could not allocate the required stock, and so it should reverse the confirmation. We will do this by again using events. The Stock microservice would publish an AllocationFailedEvent and the Order microservice would subscribe to that event and revert the state of the order to pending.

We have applied this pattern to our application, as shown in the following diagram:

Figure 15.2 – Compensation pattern: transfer funds

The preceding diagram shows the flow for a failure in transferring funds between accounts, as follows:

  1. The AccountController invokes the withdraw method on the AccountService...