第12章クラウドネイティブアプリケーション開発

Kubernetes is an open-source orchestration platform used for automating deployment, scaling, and management of container-based workloads. An example of a Kubernetes platform is shown in Figure 12.19.

The workload refers to an application being run on Kubernetes. The Kubernetes master node includes the control plane, which has several important components, including a service controller, node controller, endpoint controller, replication controller, and scheduler. These components are responsible for features such as load balancing by distributing network requests across containers efficiently; self-healing containers by regularly checking them for good health and where failed containers are replaced or restarted automatically; auto-scaling containers by adding or removing them in accordance with demand; automated deployment to handle setting up and deploying containers to the cloud; storage management to handle the storage needs of all the containers; and handling networking between containers.

The Kubernetes master node comprises several components, including the Kubernetes API server, which plays a crucial role in managing container-based workloads. Additionally, the Kubernetes cluster consists of worker nodes, each containing a kubelet. Working in tandem with the master node, the kubelet handles tasks like scheduling and ensuring the smooth operation of applications deployed within the worker nodes. Kubernetes has evolved into the preferred platform for deploying cloud-native applications. In this ecosystem, the microservices of a cloud-native application interact over the network, deployed and scaled within a Kubernetes cluster.

To deploy a cloud-native application in a Kubernetes environment, microservice containers, pulled from a registry, are deployed in pods. A pod is a small logical unit that runs a container within a worker node in the Kubernetes cluster. A cluster is a set of one or more nodes. Pods are a group of one or more containers with shared storage network resources and a specification for how the containers are run. Containers should only be scheduled together in a single pod if they are tightly coupled and need to share resources. Pods are ephemeral, meaning they are nonpermanent resources. Kubernetes manages the pods rather than the containers directly. The API server on the Kubernetes master node communicates with the worker node to deploy the container in a pod and start it up. Replicas of pods can be increased to scale the containerized microservice within it. If a pod fails, a new one is created. Kubernetes manages these deployments for the length of the deployment until the pod is deleted. In other words, it ensures that all pods and replicas are running.

Service discovery is another important service provided by the Kubernetes platform. As pods are added and replicated, an internal IP address is provided for the pod, making the container accessible. Pods are ephemeral so IP addresses can change as new pods are created. Service registry and service discovery capabilities address this issue by creating Kubernetes services. A Kubernetes service is an abstraction, which defines a logical set of pods and a policy by which to access them in a reliable way.

Given the fact that many tools are available for containerization and container orchestration, what justifies the broad acceptance of Docker and Kubernetes to handle these respective functions?

Terraform is an open-source IaC tool used to build, update, and version cloud and on-premises resources. Some use cases for Terraform include managing Kubernetes clusters and provisioning resources in the cloud, among many others.

GitLab is a cloud-based DevOps platform used to monitor, test, and deploy application code. GitLab includes a cloud-based Git repository as well as several DevOps features such as CI/CD, security, and application development tools. The CI/CD tool can be used to automate testing, deployment, and monitoring applications. GitLab can also be used for security analysis, static analysis, and unit testing. GitHub is a cloud-based developer platform used for software development, collaboration, and security. GitHub also includes a cloud-based Git repository and several DevOps features similar to GitLab.