Pods can do horizontal autoscaling (i.e., grow or shrink the number of instances), and perform rolling updates and canary deployments. When scaling back down or upgrading to a new version, for instance, pods eventually die. Pods are ephemeral, with a limited lifespan. A pod represents a running process on a cluster. Cluster NodesĪlternatively, pods can be used to host vertically-integrated application stacks, like a WordPress LAMP (Linux, Apache, MySQL, PHP) application. The Scheduler is responsible for the scheduling of containers across the nodes in the cluster it takes various constraints into account, such as resource limitations or guarantees, and affinity and anti-affinity specifications. The Cloud Controller Manager integrates into each public cloud for optimal support of availability zones, VM instances, storage services, and network services for DNS, routing and load balancing. The Controller Manager is a daemon that runs the core control loops, watches the state of the cluster, and makes changes to drive status toward the desired state. There are various controllers to drive state for nodes, replication (autoscaling), endpoints (services and pods), service accounts and tokens (namespaces). Controllers work to drive the actual state toward the desired state. Most resources contain metadata, such as labels and annotations, desired state (specification) and observed state (current status). Clients authenticate via the API Server, and also use it as a proxy/tunnel to nodes and pods (and services). It also acts as the gateway to the cluster, so the API server must be accessible by clients from outside the cluster. The API Server provides APIs to support lifecycle orchestration (scaling, updates, and so on) for different types of applications. These can all run on a single master node, or can be replicated across multiple master nodes for high availability. As the above illustration shows, the control plane is made up of three major components: kube-apiserver, kube-controller-manager and kube-scheduler. It continuously manages object states, responding to changes in the cluster it also works to make the actual state of system objects match the desired state. The control plane is the system that maintains a record of all Kubernetes objects. On the other hand, you can also integrate Kubernetes into your environment and add additional capabilities. It allows you to consume its functionality a-la-carte, or use your own solution in lieu of built-in functionality. Kubernetes is a very flexible and extensible platform. In the early years of the project, it mostly ran stateless applications, but as the platform has gained popularity, more and more storage integrations have been developed to natively support stateful applications. While Kubernetes runs all major categories of workloads, such as monoliths, stateless or stateful applications, microservices, services, batch jobs and everything in between, it’s commonly used for the microservices category of workloads. It allows developers to build customized workflows and higher-level automation to deploy and manage applications composed of multiple containers. It aims to reduce the burden of orchestrating underlying compute, network, and storage infrastructure, and enable application operators and developers to focus entirely on container-centric workflows for self-service operation. It could be thought of as the operating system for cloud-native applications in the sense that it’s the platform that applications run on, just as desktop applications run on MacOS, Windows, or Linux. It’s used for the deployment, scaling, management, and composition of application containers across clusters of hosts.īut Kubernetes is more than just a container orchestrator. It provides a container runtime, container orchestration, container-centric infrastructure orchestration, self-healing mechanisms, service discovery and load balancing. Kubernetes: More than just container orchestrationĪs stated before (but is worth stating again), Kubernetes is an open source platform for deploying and managing containers. Discovering and Publishing Services in Kubernetes.
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