Architecture

Question 1

What is Kubernetes basically?

Answer 1

An orchestrator for microservice apps

Question 2

What is a microservice app?

Answer 2

It is a name for an application that’s made up of lots of small and independent services.

Question 3

How does Kubernetes basically works?

Answer 3

It organizes things so that they work on the right networks with the right secrets. That is called orchestration.

Question 4

How does a typical K8s cluster look like?

Answer 4

It has masters and nodes. Masters are in charge and decide which node does what. Nodes do the work.

Question 5

How do we package code for Kubernetes?

Answer 5

We have Kubernetes deployment where we define the process inside a yml file. It tells K8s how our app should like e.g. ports, how many replicas. We give the file to master in Kubernetes and it deploys the app on the cluster

Question 6

Describe the platform agnostic property of K8s

Answer 6

It is platform agnostic. It runs on Linux but it is not interested on which platform this Linux runs; bare metal or VM etc.

Question 7

How is master structured?

Answer 7

It’s a bunch of moving parts. They all run on a single server. We don’t run user workloads on master, it orchestrates nodes.

Question 8

What is kube-apiserver (apiserver)?

Answer 8

It is the front-end to the control plane. It’s the only master component that we should be talking to so also known/called as master. It exposes a RESTful API and it consumes JSON. By default it exposes on port 443

Question 9

What is cluster store?

Answer 9

If the apiserver is the brain of the master, that’s the memory of it. The config and the state of the cluster is persistently stored here. It uses etcd as Cluster Store

Question 10

What is etcd?

Answer 10

etcd is a distributed key value store that provides a reliable way to store data across a cluster of machines.. KV store is a noSQL database. It’s distributed, consistent and watchable.

Question 11

What is kube-controller-manager?

Answer 11

It’s the controller of controllers. At the moment it implements some features like Node controller, Endpoints controller, Namespace controller. These controllers watch for changes and help maintain desired state. They are all controlled by controller manager.

Question 12

What is kube-scheduler?

Answer 12

This watches api-server for new pods and assigns work to nodes. It has to think about a lot of things like affiity/anti-affinity, constraints, resources etc.

Question 13

What are nodes?

Answer 13

A.k.a. Minions. They are K8s workers. There are basically 3 components that we care about; kubelet, container runtime and the kube proxy.

Question 14

What is Kubelet?

Answer 14

It is the main Kubernetes agent on Node and referred as Node. Registeres node with cluster. Watches the apiserver on master for work assignments. Any time it sees one, it carries out the task and reports back to master. Instantiates pods????? If the pod fails for some reason, it reports back to master and it does not try to restart it or find another node to run it. It’s masters responsibility to make decision at that point. It exposes and endpoint at localhost on port 10255 (it lets you inspect the spec of the Kubelet). /spec end point gives some info, /healthz for health check and /pods for running pods and much more.

Question 15

What does Container Engine do?

Answer 15

It does container management like pulling images, starting/stopping containers, etc. It’s usually docker but its pluggable and can be rkt if one wants.

Question 16

What is kube-proxy?

Answer 16

It’s networking brain of the node. It makes sure that every pod gets it unique id and all containers in a pod shares a single IP. It also makes load balancing. Load balances across all pods in a service. A service is a way to hide multiple nodes behind a single network address.

Question 17

What is the model that K8s operates on?

Answer 17

It’s a declarative model. We give it a YAML or JSON manifest file where we describe how the app should look like. We do not give the commands needed for that. We just tell how we want it to look like. It’s up to K8s how to get there.

Question 18

What happens when desired state and actual state diverges?

Answer 18

It should bring desired state back. It runs a lot of reconciliation loops that constantly checks the actual state matches the desired state.

Question 19

What is a pod?

Answer 19

The atomic units of scheduling in VMs is the VM, Container in docker world and Pod in K8s. Containers always run inside of pods. Pods can have multiple containers.

Question 20

What does a pod do and have?

Answer 20

It is a ring-fenced environment that runs containers. It has a network stack and kernel namespaces. It is also the unit of scaling.

Question 21

How is the env arranged if more than one container are run inside a pod?

Answer 21

All containers in pod share the same environment. e.g. they have the same IP. If they want to talk each other there is localhost interface in there.

Question 22

When should one use more than one container inside one pod?

Answer 22

If there are tightly coupled applications (e.g. 2 apps sharing the same DB, or a logging application(sidecar container) for a web server(main container)) we can put them together. But for loosely coupled apps no need for that. Also for scaling we should add more pods not more containers inside a pod.

Question 23

How is the lifecycle of a pod?

Answer 23

They have 3 phases: pending, running, succeeded/failed. Once they die they can not be restarted back.

Question 24

How do we deploy pods?

Answer 24

They are usually part of a bigger system but we can also deploy them alone by giving apiserver a manifest file. apiserver reads the file and deploys it to a suitable Node. They are usually deployed via higher level objects like Replication Controller.

Question 25

Can we rely on pod IPs?

Answer 25

No. Each time a pod dies and a new one is created, it gets a new IP.

Question 26

What are services?

Answer 26

Service is a Kubernetest obect just as Pod and Node. We define it inside yml file. E.g. we can set up an IP server between FE and db nodes to fix IP address and DNS. It can load balance requests among different pods.

Question 27

How are services and pods tied?

Answer 27

The way that a pod belongs to a service is via labels. These labels tie services and pods. So if we give same labels that we give to normal pods to an irrelevant one, it will be load balanced through service as well. Also you can upgrade to a new version or return back to an older version by just changing labels on service.

Question 28

What are basic properties of services?

Answer 28

• They only send requests to healthy pods
• They can be configured for session affinity
• They can point to things outside cluster
• They make random load balancing
• They use TCP by default

Question 29

What can be said about Services?

Answer 29

Deployments are all about declaretiveness. You do not say K8s how to do but rather tell what you want. They are self documenting, spec-once deploy-many, versioned, simple rolling updates and rollbacks. They are defined via YAML or JSON manifests and deployed via apiserver. As replication controllers add features around, these do the same.

Question 30

Can multiple versions be run with deployments?

Answer 30

We can run multiple concurrent versions at the same time either in blue-green deployments or in canary releases.

Question 31

What is Minikube?

Answer 31

It’s all about spanning your local environment on your laptop.

Question 32

What are some types of installations for Kubernetes?

Answer 32

Minikube, Google Container Engine(GKE), AWS Provider, Manual Install