Kubernetes architecture has mainly 3 components and they are the Master Nodes, the Worker Nodes and the distributed key-value stores like etcd. Hi! A master node hosts the Kubernetes Control Plane, a set of services that administrate and orchestrate the whole cluster. So why does that happen? The Controller Manager handles cluster orchestration. The master server consists of various… Etcd is a distributed key value data store. And it will do some magic with NAT and conntrack and things like that. Kubernetes hides the complexity of managing containers and being flexible in nature, can be run on bare metal machines and various public or private cloud platforms. Again, they’re running as pods. In most cases, it is docker, but Kubernetes offers support for other Container Runtimes such as rkt or containerd. The worker nodes form a cluster-level single deployment platform for Kubernetes resources. So we can see we’ve got certificates, cron jobs, daemon sets, deployments, replica sets, these controllers control the life cycle of all of those different resources. But kube-proxy is the component that’s responsible for programming, and that’s why it has to run on every single node. And in this episode we’re going to look at the architecture of Kubernetes. It explains the architecture and features like api-server, scheduler, etcd, and control manager. It yields pods virtual network interfaces and local IP addresses. My name is John and I'm a Senior Cloud Native Architect @ VMware where I work with customers to help design and implement Kubernetes solutions, in addition to contributing back to upstream open source projects. The control plane is in constant contact with your compute machines. A cluster has at least one worker node and at least one master node. The Components of Kubernetes Architecture There are mainly two components of the architecture: Master nodes (Also known as Control Plane) Worker nodes (Also known as … If you’re more used to a VM-centric view of the world, you can think of our control plane like vCenter and our nodes like ESXi hosts. So via kubectl or via any other toolings like client libraries in different languages, plugins, etc. I’m going to put that link in the show notes. We start with a basic overview of the Kubernetes cluster architecture. So you should definitely check that out if you want more information. In this tutorial, we will discuss Kubernetes architecture (master node components) and the moving parts of Kubernetes and also what are the key elements, what are the roles and responsibilities of them in Kubernetes architecture. It’s possible to have a multi-master setup (for high availability), but by default there is a single master server which acts as a controlling node and point of contact. Once you’ve authenticated, do I actually have the permission to do what I want to do? So it’s important to note that the API server is the only thing that talks to etcd. A cluster is a set of machines, called nodes, that run containerized applications managed by Kubernetes. In this blog, we will discuss Kubernetes architecture and the moving parts of Kubernetes and also what are the key elements, what are the roles and responsibilities of them in Kubernetes architecture. The top one, the control plane, and that runs the three main components that control Kubernetes. We see what their roles and responsibilities are and how they are configured. Well the controller for deployments creates the replica set, writes that information back into etcd, and then there’s a replica set controller which looks at that information via the API server, pulls it out, and then does something else. Now we actually need to pick something up and run it. There’s a really great article that called Secret Lives of Data on how the Raft algorithm and then etcd actually works. My name is John Harris, and I’m a Senior Cloud Native Architect at VMware. The architectural concepts behind Kubernetes. So the second piece of our puzzle is etcd. So, let’s see its components: First introduced in 2014 by Google, and now maintained by the Cloud Native Computing Foundation, Kubernetes is a powerful and popular container orchestration system built on a cluster architecture. It is the entry point of all administrative tasks. Nodes. The master node is the most vital component of Kubernetes architecture. This is where the second part of our control plane comes in, the controller manager. That needs to be running on our worker node. A Kubernetes cluster is usually deployed across several nodes : from single-node clusters up to 5000-node large clusters. Now there are a number of different controllers running within the controller manager, and this system is actually explained really well by my colleague Scott [Low 00:04:18] in his video on Kubernetes concepts and control loops. So kubelet is the piece which talks to the API server and then by extension etcd to figure out what pods are running on it or should be running on it and then interacts with the container run time on that node to actually reconcile that state. And we’ll talk about what all of these components do later on in the video. The two components of a Kubernetes environment include: Master – This is the centralized management of a Kubernetes … A Kubernetes cluster consists of a set of worker machines, called nodes A node is a worker machine in Kubernetes., that run containerized applications. And it has a number of different responsibilities. Each Kubernetes cluster consists of two sets of components: (1) the control plane which is used to manage operations throughout the cluster, and (2) the cluster’s worker nodes which run containerized applications in pods. And if you want to see all the controllers that run in the controller manager, you can just head to the Kubernetes Kubernetes Package Controller directory on GitHub. It does reads from etcd and does writes from etcd. The API will store this configuration in the ETCD, and the Sheduler will assign your application pods to worker nodes. hbspt.cta._relativeUrls=true;hbspt.cta.load(5129574, '49e69293-1ec9-4d4c-acd4-3604703ed444', {}); Hadrien is a Site Reliability Engineer (SRE) at Padok. Containers vs. Containerized Applications? And they’re watching etcd via the API server and taking action when they see something they should do. A Pod represents a set of running containers on your cluster. Kubernetes is an architecture that offers a loosely coupled mechanism for service discovery across a cluster. On the bottom left, we have our nodes. When you deploy Kubernetes, you get a cluster. The API server, the scheduler, and the controller manager. Controllers. The control plane makes sure it does. Kubernetes Architecture. Create your own profile on KubeAcademy to track your progress, save your favorite courses and lessons, earn achievements, partake in discussions, and more. So the API server is stateless. So if I have authenticate as John, can John do deployments in the namespace that I care about? But kube-proxy really watches the Kubernetes API server, and by extension etcd, for new services and it program’s iptables rules on all of the nodes so that pods can talk to each other via their IP addresses. They’re all in separate repositories. So I hope this introduction was useful in explaining what all the pieces of the Kubernetes architecture are. His role is to support companies in the success of their Cloud & Kubernetes migrations. This is etcd, which is a distributed key value store. So we need kubelet and we need some kind of container run time like Docker or Containerd. Advancing to the next lesson in 5 seconds…. This is where your actual workloads are going to run. So the first component that we want to look at is our API server. But then there’s authentication to make sure we are who we say we are using one of the various authentication methods. C ontainers have become the definitive way to develop applications because they provide packages that contain everything you need to run your applications. Following are the key components of Node server which are necessary to communicate with Kubernetes master. Wherein, we have master installed on one machine and the node on separate Linux machines. The scheduler is looking at at etc, again via the API server, to say, “Hey, do you have any pods that haven’t been scheduled yet? Kubernetes follows a client-server architecture. Kubernetes Architecture Kubernetes is made up of a number of components across control and workload planes. The API server puts every HTTP request on the kubelet API for executing the pods definition from worker nodes’ manifested files. The first requirement of each node is Docker which helps in running the encapsulated application containers in a relatively isolated but lightweight operating environment. It’ll then do authorization. Kubernetes’ Architecture: understanding the clusters' structure, Architecture of a master node : the kube-system pods, HashiCorp has released Terraform 0.14: my experience. They could run collocated with a control plane in what we call a stacked configuration, but we like to run them separately because they have a slightly different backup, restore, and performance profile. ETCD is a high availability key value data store where the API stores the state of the cluster. It functions based on a declarative model and implements the concept of a ‘ desired state.’ These steps illustrate the basic Kubernetes process: So there’s a deployment controller in here which is looking at etcd via the API server saying, “Hey, there’s a new deployment, I got to do something.” Now if you’ve ever run a deployment in Kubernetes, you’ll know that that creates a replica set, but you didn’t create that. How to share a filesystem on AWS EKS with EBS volumes? Thanks for joining us and we hope to see you in another video. Kube proxy, the container network interface and kube DNS will then ensure that the created pods have network access and can communicate with other pods on the node and in the cluster. And all it’s really responsible for doing is programming iptables, in most cases. Kubernetes architecture. The worker node (s) host the pods that are the components of the application. The master … So if you lose one, you’re still okay. It communicates with the different components of the master and the worker nodes to apply the user-desired state. Every cluster has at least one worker node. However, it wouldn’t be possible to manage all these pods manually; that is where the Kubernetes Control Plane has a role to play. We deployed a mini-kubernetes setup inside a docker container, and deployed our fist pod. Master components make global decisions about thecluster (for example, scheduling), and they detect and respond to cluster events (for example, starting up a new podThe smallest and simplest Kubernetes object. It provides a container runtime, container orchestration, container-centric infrastructure orchestration, self-healing mechanisms, service discovery and load balancing. Uses the Raft algorithm to do leader election, low replication. This is what you interact with when you write `kubectl` commands. So everything talks to etcd via the API server. And that’s all inside iptables. And this is the main entry point to the cluster. What are Kubernetes Clusters vs. This is also where credentials required to authenticate the requests you send to the API are stored. A running Kubernetes cluster contains node agents (kubelet) and master components (APIs, scheduler, etc), on top of a distributed storage solution.This diagram shows our desired eventual state, though we're still working on a few things, like making kubelet itself (all our components, really) run within containers, and making the scheduler 100% pluggable. The scheduler monitors the available resources on the different worker nodes and schedules pods and other Kubernetes resources to nodes in consideration of this. And you can have any number of those connected to your cluster within reason. And this is where our worker node components start to come in. Nodes vs. Pods vs. Kubernetes Architecture and Concepts. Post your questions in the Kubernetes community Slack. The master node has various components, such as: This lesson will walk through what each component does and how they work together. Kubelet acts as a component within the worker architecture accountable for the node level management of pods. Hey, everyone. It also ensures that every container is working healthily. Kubernetes Architecture and Components. Join the discussion here. If you want to learn more about Kubernetes and how to use it in a production environment, you can check out our other blog articles and follow Padok on social media. … Kubernetes Components. Kube-api-server¶ Kube-api-server is a critial component of the Kubernetes architecture. when a deployment’s replicas field is unsatisfied).Master components can be run on any machine in the cluster. Have feedback about this course or lesson? These master components are pretty much the brain of the Cluster and therefore are critical components to Kubernetes. These services run as pods in the "kube-system" namespace. On the worker nodes, Kubelet will receive the description of its scheduled pods and will notify the container runtime to run them. It’s just changing information then writing things back into etc. Cloud Controller Manager. You send the description of your application and its configuration to the API on the master node through the `kubectl` command line utility. Now let's get into situation and review what exactly goes on when you deploy your containerized application on a Kubernetes cluster. Questions about this lesson are best suited for the #kubernetes-users channel. The applications can vary in sizes: from hundreds to thousands of nodes. Welcome to KubeAcademy. On the bottom right is our data or persistence layer. GitHub CLI 1.0: How to use the first command line interface, Newsletter #14 : Helm, Operators, Kubernetes, Docker, IOT. There are clusters with a single node that acts as both a master and a worker, as well as some High Availability clusters where the Control Plane components are scattered across different nodes, and even replicated for resilience. The Kubernetes Service Proxy acts as a load balancer. Now there’s one other piece of the puzzle. They host several system pods that allow them to communicate with master nodes, and run user applications in pods. Kubelet Service In case of a node failure, it will spin up new pods on the remaining nodes to match the wanted replica count. So this is where the scheduler comes in. This tutorial walks you through the Kubernetes architecture and the control plane and worker node components. Under worker nodes, we cover details about kubectl, kubelet, and kube-proxy. Cluster Architecture. And kubelet’s talking back to the API server and saying, “Hey, I am node A,” let’s say, “What pods are running on, or what pods should be scheduled on node A?” It gets that information from etcd and then it compares that with the information it actually has running. As it ensures pods run according to configuration, the Kubelet agent also runs on master nodes. And you can see all of them listed out. Do you have any pods that are waiting to go somewhere?” It will read that out and it’ll say, “Hey, yeah, like I’ve got three pods, maybe that need to be scheduled.” It’ll take things into account like taints and tolerations where the pods should be scheduled, availability zones maybe, and then it’ll write the name of a node into that pod and it will again write it back to etc. That’s where actual all the work happens. Now what actually happens? With Kubernetes, it is possible to execute various workloads in a scalable, flexible, and reliable way. Okay, so now we’ve written our replica set, we’ve written our pod information back into etcd. Not yet a part of the Kubernetes Slack community? The CNI creates virtual networks across the whole cluster to allow containers and pods to communicate regardless of what node they run on. Regardless of the number of nodes, a Kubernetes cluster will always have the same general architecture : at least one master node and several worker nodes. It also does a little bit of validation on your resources that you deploy to it, so kubectl or client-side libraries also do client-side validation to make sure they’re not just sending garbage to the API server, but the server does a little bit of validation, too. We want to hear it! We first look at the architecture at a high level, and then we drill down into each of these components. Iptables is used to satisfy services in Kubernetes. So we’re going to see how this all works. This guide gives you a high-level overview of the architecture and moving parts of a Kubernetes setup. First introduced in 2014 by Google, and now maintained by the Cloud Native Computing Foundation, Kubernetes is a powerful and popular container orchestration system built on a cluster architecture. We still haven’t actually done anything. Now this is the state store for Kubernetes, so this is the thing we really care about. Like I said, these usually run on three separate nodes to the control plane. So in this first slide you can see the architecture of a cluster. Kubernetes Architecture and Components Kubernetes has a decentralized architecture that does not handle tasks sequentially. Kubernetes architecture. Here are the key components and how they fit into the picture. Home > Artificial Intelligence > Kubernetes Cheat Sheet: Architecture, Components, Command Sheet Kubernetes has become an essential part of industries and is changing the world of technology. So kube-proxy is a piece which runs as a daemon set on all of our nodes. In order to get a deeper understanding, you are highly encouraged to deploy each of the components separately and setup their communication from scratch. You’ve configured your cluster to run a certain way. The scheduler ensures the workload is evenly balanced across the cluster. It also reports to the master the health of the node. There is always one node to check for fault tolerance. Kubernetes (also known as k8s) is a platform for automating deployment, scaling, and management of containerized applications. It does some admission control, which is maybe doing some additional validation or mutation of the request before it persists it. Janet Kuo, the co-chair of KubeCon, addressed the Kubernetes features and its importance in the coming time. Kubernetes Architecture: An Introduction to Kubernetes Components. Unlock your full potential with Kubernetes courses designed by experts. Kubernetes is made up of a number of components across control and workload planes. In this case probably create pods. A Kubernetes environment consists of several components, hardware and software, which all work together to manage the deployment and execution of containerized applications. Kubernetes: part 1 – architecture and main components overview # docker # kubernetes Arseny Zinchenko Jul 25, 2019 Originally published at rtfm.co.ua on Jul 25, 2019 ・15 min read The Kubernetes DNS Service allow pods to communicate with each other using their name or FQDN (Fully Qualified Domain Name) instead of their local IP. You usually run three, one on each control plane node. We have three main groups that we care about here. The API server is the central part of the Kubernetes Control Plane, it is a REST API which is the entrypoint to issue commands to the cluster. It oversees nodes leaving and joining the cluster and ensures the current state of the cluster is always in check with the desired state stored in ETCD. Read Now! In order to have a resilient Kubernetes cluster, there should be at least 3 ETCD instances. All right, let’s dive in. The Kube-api-server is an API use by every components of the master components. Kubernetes is a robust yet complex infrastructure system for container orchestration, with multiple components that must be adequately protected. Kubernetes Architecture. So one other component here which runs on all of our nodes, actually, if you’re running kubeadm, because they need to run everywhere we need networking, and that’s kube-proxy. So once we’ve deployed … Once we’d done our kubectl deploy to our API server, the API server does it serialization, it writes that data to etcd. Docker. So it’s not actually telling a node to do anything at this point. Kubernetes has a flexible architecture which provides for a loosely-coupled mechanism for service discovery. Send your thoughts to KubeAcademy@VMware.com. Kubernetes is an open-source platform for deploying and managing containers. If a pod fails, it may be rescheduled on any worker node following the same procedure. Kubernetes - Node Components. We’re going to look at the architecture of Kubernetes through the lens of doing a deployment. The Container Runtime is the service that runs containers. So we can really see this flow of everything going to etcd via the API server reads and writes. Kubernetes architecture In any case, all the components listed here are always present and interact with each other as explained above. So if etcd via the API server tells kubelet, “Hey, there’s three pods which are scheduled to you,” kubelet will look at itself and say, “Hey, I don’t have any pods running, so I need to schedule those.”. And if you’re interested more in services in more detail, you should check out my colleague Timmy [Car’s 00:06:53] video on services. The cluster structure presented in this article is fairly standard, but is not the only one possible. A Kubernetes cluster is usually deployed across several nodes : from single-node clusters up to 5000-node large clusters. The third part of our control plane. These core Kubernetes components handle the important work of making sure your containers are running in sufficient numbers and with the necessary resources. It’ll then do serialization of that request, so our deployments, going to serialize it into a particular format and then it’s going to write that to etcd. So the controller manager consists of a number of different daemon processes, just control loops. Kubelet communicates with the API and applies the resources configuration on the node. Master components provide the cluster’s control plane. So you can kind of think of the kubelet a little bit as a control loop as well. It routes network traffic and forwards services to expose them outside of the cluster. A Kubernetes cluster has one or more control planes, and one or more compute nodes. A running Kubernetes cluster contains node agents (kubelet) and master components (APIs, scheduler, etc), on top of a distributed storage solution.This diagram shows our desired eventual state, though we're still working on a few things, like making kubelet itself (all our components, really) run within containers, and making the scheduler 100% pluggable. Kubernetes contains two major components that provide the functionality to provision, manage, monitor, and orchestrate containers. This lesson will walk through what each component does and how they work together. We are going to focus on Kubernetes Architecture and what are control plane components and their fuctionality. Firstly, it’s serves the Kubernetes API, obviously. So we also need a kubelet on those nodes, as well. Control Plane-Node Communication. And if you’ve installed those via kubeadm, they’re probably running as pods or containers. And that’s really just a fancy way of saying it keeps all the data in sync between the three nodes. Kubernetes Control Plane is responsible for managing the life-cycle of the pods and handle all of the details. And we usually run three of those for high availability. From a high level, a Kubernetes environment consists of a control plane (master), a distributed storage system for keeping the cluster state consistent (), and a number of cluster nodes (Kubelets). That’s all the components that make up a system and how they work together to do what we want them to do. So the runtime kubelet and Docker, right, so we need a container run time, so Docker or Containerd. Conceptual Architecture of Kubernetes — Image by Author. There are other compatible CRI run times as well. 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