Deployments and YAML Manifests

Posted by Belbinson Toby , Thursday, April 30, 2020 8:50 PM



A deployment represents one or more identical pods, managed by the Kubernetes Deployment Controller. A deployment defines the number of replicas (pods) to create, and the Kubernetes Scheduler ensures that if pods or nodes encounter problems, additional pods are scheduled on healthy nodes.

You can update deployments to change the configuration of pods, container image used, or attached storage. The Deployment Controller drains and terminates a given number of replicas, creates replicas from the new deployment definition, and continues the process until all replicas in the deployment are updated.

Most stateless applications in AKS should use the deployment model rather than scheduling individual pods. Kubernetes can monitor the health and status of deployments to ensure that the required number of replicas run within the cluster. When you only schedule individual pods, the pods aren't restarted if they encounter a problem, and aren't rescheduled on healthy nodes if their current node encounters a problem.

If an application requires a quorum of instances to always be available for management decisions to be made, you don't want an update process to disrupt that ability. Pod Disruption Budgets can be used to define how many replicas in a deployment can be taken down during an update or node upgrade. For example, if you have 5 replicas in your deployment, you can define a pod disruption of 4 to only permit one replica from being deleted/rescheduled at a time. As with pod resource limits, a best practice is to define pod disruption budgets on applications that require a minimum number of replicas to always be present.

Deployments are typically created and managed with kubectl create or kubectl apply. To create a deployment, you define a manifest file in the YAML (YAML Ain't Markup Language) format. The following example creates a basic deployment of the NGINX web server. The deployment specifies 3 replicas to be created, and that port 80 be open on the container. Resource requests and limits are also defined for CPU and memory.



0 comments

Pods

Posted by Belbinson Toby , 8:34 PM


Kubernetes uses pods to run an instance of your application. A pod represents a single instance of your application. Pods typically have a 1:1 mapping with a container, although there are advanced scenarios where a pod may contain multiple containers. These multi-container pods are scheduled together on the same node, and allow containers to share related resources.

When you create a pod, you can define resource requests to request a certain amount of CPU or memory resources. The Kubernetes Scheduler tries to schedule the pods to run on a node with available resources to meet the request. You can also specify maximum resource limits that prevent a given pod from consuming too much compute resource from the underlying node. A best practice is to include resource limits for all pods to help the Kubernetes Scheduler understand which resources are needed and permitted.

For more information, see Kubernetes pods and Kubernetes pod lifecycle.
A pod is a logical resource, but the container(s) are where the application workloads run. Pods are typically ephemeral, disposable resources, and individually scheduled pods miss some of the high availability and redundancy features Kubernetes provides. Instead, pods are usually deployed and managed by Kubernetes Controllers, such as the Deployment Controller.

0 comments

Nodes and node pools

Posted by Belbinson Toby , 8:22 PM


To run your applications and supporting services, you need a Kubernetes node. An AKS cluster has one or more nodes, which is an Azure virtual machine (VM) that runs the Kubernetes node components and container runtime:
  • The kubelet is the Kubernetes agent that processes the orchestration requests from the control plane and scheduling of running the requested containers.

  • Virtual networking is handled by the kube-proxy on each node. The proxy routes network traffic and manages IP addressing for services and pods.

  • The container runtime is the component that allows containerized applications to run and interact with additional resources such as the virtual network and storage. In AKS, Moby is used as the container runtime.

The Azure VM size for your nodes defines how many CPUs, how much memory, and the size and type of storage available (such as high-performance SSD or regular HDD). If you anticipate a need for applications that require large amounts of CPU and memory or high-performance storage, plan the node size accordingly. You can also scale out the number of nodes in your AKS cluster to meet demand.

In AKS, the VM image for the nodes in your cluster is currently based on Ubuntu Linux or Windows Server 2019. When you create an AKS cluster or scale out the number of nodes, the Azure platform creates the requested number of VMs and configures them. There's no manual configuration for you to perform. Agent nodes are billed as standard virtual machines, so any discounts you have on the VM size you're using (including Azure reservations) are automatically applied.

If you need to use a different host OS, container runtime, or include custom packages, you can deploy your own Kubernetes cluster using aks-engine. The upstream aks-engine releases features and provides configuration options before they are officially supported in AKS clusters. For example, if you wish to use a container runtime other than Moby, you can use aks-engine to configure and deploy a Kubernetes cluster that meets your current needs



0 comments

Control Plane

Posted by Belbinson Toby , 8:10 PM


When you create an AKS cluster, a control plane is automatically created and configured. This control plane is provided as a managed Azure resource abstracted from the user. There's no cost for the control plane, only the nodes that are part of the AKS cluster.
The control plane includes the following core Kubernetes components:
  • kube-apiserver - The API server is how the underlying Kubernetes APIs are exposed. This component provides the interaction for management tools, such as kubectl or the Kubernetes dashboard.

  • etcd - To maintain the state of your Kubernetes cluster and configuration, the highly available etcd is a key value store within Kubernetes.

  • kube-scheduler - When you create or scale applications, the Scheduler determines what nodes can run the workload and starts them.

  • kube-controller-manager - The Controller Manager oversees a number of smaller Controllers that perform actions such as replicating pods and handling node operations.

AKS provides a single-tenant control plane, with a dedicated API server, Scheduler, etc. You define the number and size of the nodes, and the Azure platform configures the secure communication between the control plane and nodes. Interaction with the control plane occurs through Kubernetes APIs, such as kubectl or the Kubernetes dashboard.

This managed control plane means that you don't need to configure components like a highly available etcd store, but it also means that you can't access the control plane directly. Upgrades to Kubernetes are orchestrated through the Azure CLI or Azure portal, which upgrades the control plane and then the nodes. To troubleshoot possible issues, you can review the control plane logs through Azure Monitor logs.

If you need to configure the control plane in a particular way or need direct access to it, you can deploy your own Kubernetes cluster using aks-engine.

0 comments

Kubernetes cluster architecture

Posted by Belbinson Toby , 7:55 PM


A Kubernetes cluster is divided into two components:

  • Control plane nodes provide the core Kubernetes services and orchestration of application workloads.
  • Nodes run your application workloads.



0 comments

What is Kubernetes?

Posted by Belbinson Toby , 7:51 PM


Kubernetes is a rapidly evolving platform that manages container-based applications and their associated networking and storage components. The focus is on the application workloads, not the underlying infrastructure components. Kubernetes provides a declarative approach to deployments, backed by a robust set of APIs for management operations.

You can build and run modern, portable, microservices-based applications that benefit from Kubernetes orchestrating and managing the availability of those application components. Kubernetes supports both stateless and stateful applications as teams progress through the adoption of microservices-based applications.

As an open platform, Kubernetes allows you to build your applications with your preferred programming language, OS, libraries, or messaging bus. Existing continuous integration and continuous delivery (CI/CD) tools can integrate with Kubernetes to schedule and deploy releases.

Azure Kubernetes Service (AKS) provides a managed Kubernetes service that reduces the complexity for deployment and core management tasks, including coordinating upgrades. The AKS control plane is managed by the Azure platform, and you only pay for the AKS nodes that run your applications. AKS

0 comments

Azure Kubernetes Service (AKS)

Posted by Belbinson Toby , 3:07 AM

Azure Kubernetes Service (AKS) makes it simple to deploy a managed Kubernetes cluster in Azure. AKS reduces the complexity and operational overhead of managing Kubernetes by offloading much of that responsibility to Azure. As a hosted Kubernetes service, Azure handles critical tasks like health monitoring and maintenance for you. The Kubernetes masters are managed by Azure. You only manage and maintain the agent nodes. As a managed Kubernetes service, AKS is free - you only pay for the agent nodes within your clusters, not for the masters.
You can create an AKS cluster in the Azure portal, with the Azure CLI, or template driven deployment options such as Resource Manager templates and Terraform. When you deploy an AKS cluster, the Kubernetes master and all nodes are deployed and configured for you. Additional features such as advanced networking, Azure Active Directory integration, and monitoring can also be configured during the deployment process. Windows Server containers are supported in AKS.


0 comments
Subscribe to: Comments (Atom)