Azure Kubernetes Service

Introduction

Container:

• A container is an atomic unit of software that packages up code, dependencies, and configuration for a specific application.
• Containers allow you to split up monolithic applications into individual services that make up the solution.
• This rearchitecting of our application enables us to deploy these separate services via containers.

• Benefits:

1. Immutability - The unchanging nature of a container allows it to be deployed and run reliably with the same behavior from one compute environment to another.
2. Smaller Size - A container is similar to a VM, but without the kernel for each machine. Instead, they share a host kernel.
3. Lightweight - The container always relies on the host installed OS for kernel-specific services. The lightweight property makes containers less resource-intensive, so installing multiple containers is possible within the same compute environment.
4. Startup is fast - Containers start up in few seconds, unlike VMs, which can take minutes to start.

Container Management

• A container has a distinct life cycle that exists as a temporary machine.
• Its state passes through the stages of pending, running, and terminated.
• Container management involves deploying, upgrading, monitoring, and removing containers.

Kubernetes

• Kubernetes is a portable, extensible open-source platform for automating deployment, scaling, and the management of containerized workloads.
• Kubernetes abstracts away complex container management and provides us with a declarative configuration to orchestrate containers in different compute environments.

• A Kubernetes deployment is configured as a cluster. A cluster consists of at least one primary machine or control plane and one or more worker machines.

Azure Kubernetes Service

• AKS manages your hosted Kubernetes environment and makes it simple to deploy and manage containerized applications in Azure.
• Your AKS environment is enabled with features such as automated updates, self-healing, and easy scaling.
• Azure manages the control plane of your Kubernetes cluster for free.
• You manage the agent nodes in the cluster and only pay for the VMs on which your nodes run.

Workload Deployment to AKS

Default Workloads Running on AKS

• Namespace: kube-system
• Kind: Deployment

1. CoreDNS
   • CoreDNS is a DNS server that provides DNS resolution for services and pods within the Kubernetes cluster.
   • It translates service names and domain names into IP addresses, allowing pods to discover and communicate with each other and with services.
   • CoreDNS is usually configured to use a ConfigMap that defines its behavior and DNS rules.
2. CoreDNS-Autoscaler
   • CoreDNS-Autoscaler is responsible for scaling the CoreDNS deployment based on the load.
   • It typically uses the metrics provided by the CoreDNS pods to determine when to scale up or down.
3. Konnectivity-Agent
   • Konnectivity is a component used for connectivity between the control plane and the nodes in the cluster.
   • It helps facilitate communication between the API server and the nodes, especially in private clusters or clusters with advanced networking configurations.
4. Metrics Server
   • Metrics Server is a cluster-wide aggregator of resource usage data, such as CPU and memory metrics.
   • Metrics Server scrapes metrics from the kubelet on each node and provides this data to the Kubernetes API server for use in autoscaling and monitoring.

AKS Networking

1. Network Plugin:
   • Determines how networking is handled in the cluster (Azure CNI in this case).
   • Azure CNI provides advanced networking capabilities and integrates with Azure Virtual Network (VNet). It allows Kubernetes pods to have IP addresses from the VNet.
2. Network Policy:
   • Controls inter-pod communication (Azure Network Policies).
   • Azure defines that Azure Network Policies will be used, which allows you to define rules to control traffic flow between pods in your AKS cluster.
3. Service CIDR:
   • This CIDR block is used to allocate IP addresses for Kubernetes services such as LoadBalancers, ClusterIP services, and others.
4. DNS Service IP:
   • This IP address is used by the cluster to resolve DNS queries for services and pods.
5. Load Balancer SKU:
   • Specifies the type of Azure Load Balancer used for the cluster.