第12章クラウドネイティブアプリケーション開発

Microservices that rely on each other communicate using well-defined APIs. These APIs help configure the infrastructure layers to facilitate resource sharing across them. APIs connect microservices and containers while providing simplified maintenance and security. They enable microservices to communicate between otherwise loosely coupled services without sharing the same technology stacks, libraries, or frameworks. Cloud-native microservices use lightweight APIs that are based on protocols such as representational state transfer to expose their functionality. The architectural style for providing standards between resources so they can communicate with each other over the Web is called representational state transfer (REST).

As already mentioned, the scheduling and orchestration layer of a cloud computing framework manages the containers microservices are deployed in. As applications grow to span multiple containers deployed across multiple servers, operating them becomes more complicated. Container orchestration tools (e.g., Kubernetes) can help coordinate and schedule many containers. They can also help scale container instances to provide more computational power. For example, the orchestration tool, depicted as “Master” in Figure 12.15, deploys the microservices in containers (single instances, initially) of an application on a computing resource.

As the microservices’ consumption of the computing resources increases, additional resources are added, and the orchestration tool will start scheduling and scaling the microservices. An orchestration platform helps schedule the microservices and containers and optimizes the use of the computing resource. In contrast, a monolith application is not designed to leverage an orchestration platform and requires the use of load balancers. Other services, such as service discovery, also need to be performed manually. For example, if microservices need to communicate with one another, they cannot find the IP addresses of their respective containers and check if they are running. This is handled automatically by the orchestration platform (i.e., Microsoft AKS, Amazon AWS EKS, Google GKE). An orchestration platform typically runs workloads by placing corresponding containers into pods that run on nodes (i.e., a virtual or physical machine). Multiple nodes are typically grouped into clusters to ensure scalability. Pods are the smallest deployable units of computing; they group multiple containers, provide shared storage and network resources, and specify how to run the containers. The orchestration platform provides support when a pod that contains a running microservice container goes down. In that case, another pod is brought up rapidly and brings it within the purview of that service automatically. Figure 12.16 shows how microservice containers are scaled and managed in the case of failure.

DevOps is a methodology that combines Agile software development and IT operations to deliver software faster and of higher quality. Because DevOps and cloud native focus on different aspects of the application development process, they complement each other in facilitating agility. DevOps focuses on the principles and practices used in development and operations. A goal of DevOps is to ensure that all team members are cross-functional, so they have a single mindset on improving customer experiences, responding faster to business needs, and ensuring that innovation is balanced with security and operational needs. Cloud native, on the other hand, focuses on the application environment and how to scale and deliver software more efficiently.

The use of a DevOps pipeline to migrate an application toward a microservices architecture achieves the goals of automation, discipline, and repeatability while reducing some of the challenges already identified. As a cloud-native application works its way through the DevOps pipeline, it also moves toward continuous delivery.

Figure 12.17 shows continuous integration and continuous deployment (CI/CD), which is a set of DevOps operating principles that enable development teams to focus on rapid and frequent integrations of new code into the application in development as well as fast and frequent delivery or deployment of new iterations of the application. It allows teams to deliver code changes more frequently and reliably. A DevOps team establishes a CI/CD pipeline, which is a series of steps needed for integration and delivery or deployment that includes the build process through which the application is compiled, built, packaged, and tested. The continuous integration part automates the application compile, build, package, and testing process, enabling it to run independent of physical resources, which allows for a more consistent integration process. This improves team communication and leads to better software quality. The continuous delivery part goes a step further and automates the deployment stage as well. During this phase, the application is deployed to selected infrastructure environments. Packages built during CI are deployed into multiple environments (e.g., development, staging). The application build undergoes integration and performance tests. Finally, the application is deployed into production and made available to end users.