Containers are gaining a lot of popularity these days. They provide an easy way to run applications, without having to worry about the underlying infrastructure.
As you might imagine, managing all these containers can become quite daunting, especially if there are numerous containers. This is where orchestration tools such as Kubernetes are very useful.
Kubernetes was developed by Google and is heavily based on their internal Borg system. It is an excellent tool to manage containers, where you provide a desired state for your containers and Kubernetes takes care of everything to ensure the containers are always in that state (for example, if a pod dies, Kubernetes will automatically start a new pod for that container, to ensure that the defined number of pods are always running). Kubernetes also provides an easy process to scale the number of pods or the number of nodes.
Soon after releasing Kubernetes, Google partnered with the Linux Foundation to form the Cloud Native Computing Foundation (CNCF). Kubernetes was then made open-source, with the Cloud Native Computing Foundation acting as its guardian. A nice writeup for Kubernetes history can be found at https://en.wikipedia.org/wiki/Kubernetes.
Kubernetes is abbreviated as k8s. If you are like me and are wondering how can the word Kubernetes be possibly shortened to k8s? Well, the 8 in k8s represents the number of characters between the letters k and s in the word Kubernetes.
With the popularity of Kubernetes soaring, Microsoft recently adopted it for its Azure environment, providing Azure Kubernetes Service as a managed service. The service entered general availability in June 2018. If you are interested in reading about this announcement, a good article to read is https://redmondmag.com/articles/2018/06/13/azure-kubernetes-service-ga.aspx .
This blog is the first in the mini-series that I will be publishing about Azure Kubernetes Service. I will take you through the process of creating an Azure Kubernetes Service (AKS) Cluster and then we will create an environment within the AKS cluster using some custom docker images.
In this first blog I will introduce some key Kubernetes terminologies and map out the scenario that the blog mini-series will focus on.
Below are some of the key concepts which I believe will help immensely in understanding Kubernetes.
If you think about a pea pod, there can be one or many peas inside it. Treating each pea as a container, this translates to a pod being an encapsulation of an application container (or, in some cases, multiple containers).
As per the formal definition, a pod is an encapsulation of an application container (or, in some cases, multiple containers), storage resources, a unique network IP, and options that govern how the container(s) should run. A pod represents a unit of deployment, a single instance of an application in Kubernetes, which might consist of either a single container or a small number of containers that are tightly coupled and that share resources. A more detailed explanation is available at https://kubernetes.io/docs/concepts/workloads/pods/pod-overview/.
One key point to remember is that pods are ephemeral, they are created and at times they die as well. In that regard, any application that directly accesses pods will eventually fail when the pod dies. Instead, you should always interact with Services, when trying to access containers deployed within Kubernetes.
Due to the ephemeral nature of pods, any application that is directly accessing a pod will eventually suffer a downtime (when the pod dies, and another is created to replace it). To get around this, Kubernetes provides Services.
Think of a Service to be like an application load balancer, it provides a front end for your container, and then routes the traffic to a pod running that container. Since your applications are always connecting to a Service (the properties for the Service remain unchanged during its lifetime), they are shielded from any pod deaths. For information about services, refer to https://kubernetes.io/docs/concepts/services-networking/service/ .
Namespaces provide a logical way of grouping your Kubernetes cluster. This allows you to provide access to different resources to different sets of users. Namespaces also provide a scope for names. Names must be unique within a namespace however they do not need to be unique across namespaces. A more in-depth description can be found at https://kubernetes.io/docs/concepts/overview/working-with-objects/namespaces/
Kubernetes Control Plane (master)
The Kubernetes master (this is a collection of processes) ensures the Kubernetes cluster is working as expected by maintaining the clusters desired state.
The nodes are where the containers and workflows are run. The nodes can be virtual machines, physical machines etc. The Kubernetes master controls each node.
The diagram below shows the environment we will be deploying within our Azure Kubernetes Service (AKS) cluster.
In summary, we will deploy three pods, each running a customised nginx container. The nginx containers will be listening on non-http/https ports. As Kubernetes does not natively provide a way to route non-http/https traffic to services, we will be deploying nginx ingress controllers to enable this functionality.
Figure 1 – Infrastructure that will be deployed within the Azure Kubernetes Service cluster
In the next blog in this mini-series, we will deploy the Azure Kubernetes Service cluster.
Happy sailing and see you soon!