The configuration above tells Kubernetes to start checking the /health endpoint, after initially waiting 2 seconds, every 5 seconds. In the pod specification we've defined the following: livenessProbe: Let's create a pod that exposes an endpoint /health, responding with a HTTP 200 status code: kubectl apply -f Note that it is the responsibility of the application developer to expose a URL that the kubelet can use to determine if the container is healthy (and potentially ready).
![what is kubernetes kubelet what is kubernetes kubelet](https://datadog-prod.imgix.net/img/blog/monitoring-kubernetes-era/kubernetes-pods.png)
We will focus on HTTP health checks in the following. Health checks, or probes as they are called in Kubernetes, are carried out by the kubelet to determine when to restart a container ( liveness probes) and used by services and deployments to determine if a pod should receive traffic ( readiness probes). The following illustrations show the structure of Kubernetes Master and Node.In order to verify if a container in a pod is healthy and ready to serve traffic, Kubernetes provides for a range of health checking mechanisms. It manages pods on node, volumes, secrets, creating new containers’ health checkup, etc. It makes sure that the networking environment is predictable and accessible and at the same time it is isolated as well. It helps in forwarding the request to correct containers and is capable of performing primitive load balancing. This is a proxy service which runs on each node and helps in making services available to the external host. It manages network rules, port forwarding, etc. The kubelet process then assumes responsibility for maintaining the state of work and the node server. This communicates with the master component to receive commands and work. It interacts with etcd store to read configuration details and wright values. This is a small service in each node responsible for relaying information to and from control plane service. The first requirement of each node is Docker which helps in running the encapsulated application containers in a relatively isolated but lightweight operating environment. Kubernetes - Node Componentsįollowing are the key components of Node server which are necessary to communicate with Kubernetes master. The scheduler is responsible for workload utilization and allocating pod to new node. The kubelet is a service that runs on the Kubernetes nodes and listens to the API server for pod creation. Both of these components are essential for the provisioning of pods/containers in the cluster. In other words, this is the mechanism responsible for allocating pods to available nodes. The kubelet is a low-level Kubernetes component and one of the most important ones after the kube-apiserver. It is responsible for tracking utilization of working load on cluster nodes and then placing the workload on which resources are available and accept the workload. It is a service in master responsible for distributing the workload. This is one of the key components of Kubernetes master. The Kubernetes kubelet component in versions 1.1-1.16.12, 1.17.0-1.17.8 and 1.18.0-1.18.5 do not account for disk usage by a pod which writes to its own. The controller manager runs different kind of controllers to handle nodes, endpoints, etc. The key controllers are replication controller, endpoint controller, namespace controller, and service account controller. It works toward getting the shared state of cluster and then make changes to bring the current status of the server to the desired state.
![what is kubernetes kubelet what is kubernetes kubelet](https://assets.d2iq.com/production/uploads/posts/attachments/kubernetes-architecture-5d47dce42b203.png)
In general, it can be considered as a daemon which runs in nonterminating loop and is responsible for collecting and sending information to API server. This component is responsible for most of the collectors that regulates the state of cluster and performs a task.
![what is kubernetes kubelet what is kubernetes kubelet](https://miro.medium.com/max/1117/1*abyDaD6DLQEaWGZsszPhuA.jpeg)
Kubeconfig is a package along with the server side tools that can be used for communication. API server implements an interface, which means different tools and libraries can readily communicate with it. Kubernetes is an API server which provides all the operation on cluster using the API. It is a distributed key value Store which is accessible to all. It is accessible only by Kubernetes API server as it may have some sensitive information. It is a high availability key value store that can be distributed among multiple nodes. It stores the configuration information which can be used by each of the nodes in the cluster. Kubernetes - Master Machine Componentsįollowing are the components of Kubernetes Master Machine. The key components of master and node are defined in the following section. Wherein, we have master installed on one machine and the node on separate Linux machines. Kubernetes - Cluster ArchitectureĪs seen in the following diagram, Kubernetes follows client-server architecture. In this chapter, we will discuss the basic architecture of Kubernetes.