Containers and Kubernetes

Questions:

Running Kubernetes on vm only without cloud providers?

Develop Kubernetes enabled applications. Skafold

What is kubernetes? (Short form - k8s)
scale up the system
orchestration tool
orchestrate dockerized applications
more effective use of servers / space
What is kubernetes cluster? *
What is cloud native application?
Kubernetes vs docker

“Desired State Management”

Containers

It needs to be managed.
Networking is definitely hard.
Containers must be scheduled, distributed and load balanced.
And the data’s got to be persisted somewhere.

Kubernetes

“Kubernetes” greek word for captain or pilot of the ship.
running 1000 of containers on production
not tied to a specific cloud provider
manage resources on the cloud
if a container goes down, another container gets started, handled by a sweet system (kubernetes)
Kubernetes uses labels as “nametags” to identify things and it can query based on these labels

Kubernetes - PODS

a runnable unit of work
generally, we use only one container per pod.
a pod can hold any number of containers, but usually it only holds two (tightly coupled containers).
a pod is connected via an overlay network to the rest of the environment.
Kubernetes (works for us) by connecting the pods to the network and rest of the kubernets ecosystem.

Kubernetes - Replication Controllers

for managing any arbitrary(random) number of pods

Pod Template

for creating any number of pod copies, as much as necessary when scaling.

Provides logic for scaling the pod up or down

Through the Replication controllers, kubernetes will manage pod lifecycle, scaling up and down, rolling deployments and monitoring.

Kubernetes services

tells the rest of kubernetes environment(pods and replication controllers) what services application provides.
pods may come and go but ip addr and ports remain the same.
other service can find our service through kubernetes service discovery

it is persistent.
provides discovery.
load balances
provides VIP layer ???
identifies pods by label selector

Kubernetes - Volumes

location where containers can access or store information
for application volume is local file system

volumes maybe backed by storage backends such as: ceph, gluster(red hat), Amazon Elastic Block Store (EBS)

Kubernetes - Namespace

What is namespace?

organizing resources in namespace
virtual cluster inside a cluster

Namespaces

Minikube

minikube comes with kubernetes-dashboard namespace which is not provided on standard cluster.

kube-system (namespace)

dont’ modify

kube-public

Kubernetes

4 Namespaces Default
grouping mechanism inside kubernetes
services, pods, repliaction controllers and volumes could easily co-operate within a namespace

Nodes

maybe a vm or physical machine depending on the cluster
has the services necessary to run application containers

Kubernetes - HELM

What is Helm?

package manager for kubernetes
to package yaml files and distribute them to public / private repositories

The package manager for Kubernetes: tool for installing, upgrading and managing applications on a Kubernetes cluster.

Helm Packages (Charts)

describes how we install packages onto a Kubernetes cluster.

helm has two parts

A Client (Helm)	A Server (Tiler)
local helm client sends instructions to `tiller` in the cluster	runs inside of kubernetes cluster

install helm curl https://raw.githubusercontent.com/kubernetes/helm/master/scripts/get | bash

helm installed into /usr/local/bin/helm tiller installed into /usr/local/bin/tiller Run 'helm init' to configure helm.

Best Practices

Namespaces

virtual cluster within a cluster

Kubernetes cluster has 3 namespaces by default:

default (all the default goes here)
kube-system (no need to touch it)
kube-public (leave it alone)
display all namespaces
- $ kubens
switch to namespace
- $ kubens test

different teams should be using different namespaces:

codehub-prod
codehub-dev
fuse-ai-prod
fuse-ai-dev

istio

cross communication using
Connect, secure, control, and observe services.

spinnaker

Cloud Native Continuous Delivery Fast, safe, repeatable deployments for every Enterprise

Kubernetes Concepts

What is Kubernetes?

Kubernetes is a production-grade, open-source platform that orchestrates the placement (scheduling) and execution of application containers within and across computer clusters.

Kubernetes automates the distribution and scheduling of application containers across a cluster in a more efficient way.

What are Kubernetes Clusters?

A Kubernetes cluster consists of two types of resources:

master
- The master coordinates the cluster.
node
- Nodes are the workers that run applications.

Masters

Masters manage the cluster and the nodes that are used to host the running applications.

responsible for managing the cluster.
etcd -> single source of truth regarding the key value pairs of pods information on kubernetes cluster.
scheduler / controller as same as their name suggests.

Node

A node is a VM or a physical computer that serves as a `worker machine` in a Kubernetes cluster.

Each node consists of:
- kubelet
- kube proxy
- a container runtime, responsible for pulling the container image, unpacking and running on a machine.
- managed by The Master
A Node can have multiple pods.

A Kubernetes cluster that handles production traffic should have a minimum of three nodes.

Kubernetes Deployment (Application Management)

Deployment instructs Kubernetes how to create and update instances of our application and ***responsible for creating and updating instances of our application***

need to specify the container image for our application.
need to specify the the number of replicas that we want to run.

Kubernetes master schedules the application instances included in the Deployment to run on individual Nodes in the cluster.

Deployment Controller

continously monitors application instances

Self Healing Mechanism

If the NODE hosting an instance goes down or is deleted, the Deployment controller replaces the instance with an instance on another NODE in the cluster.

Applications need to be packaged into one of the supported container formats in order to be deployed on Kubernetes

Pods

A Pod is a group of one or more application containers (such as Docker or rkt) and includes shared storage (volumes), IP address and information about how to run them.

can contain different different application containers.
Pods are the atomic unit on the Kubernetes platform.
When we create a Deployment on Kubernetes, that Deployment creates Pods with containers inside them (as opposed to creating containers directly)
Pods are mortal
In case of Node failure, identical pods are scheduled on other available Nodes in the cluster.

Kubernetes Services

A Service in Kubernetes is an abstraction which defines a logical set of Pods and a policy by which to access them.

Although each Pod has a unique IP address, those IPs are not exposed outside the cluster without a Service.
Services allow our applications to receive traffic.
A Service routes traffic across a set of Pods.

$ kubectl expose deployment hello-node --type=LoadBalancer --port=8080

Services can be exposed in different ways by specifying a type in the ServiceSpec:

Cluster IP(default)	NodePort	Load Balancer	External Name
Exposes the Service on an internal IP in the cluster.	Exposes the Service on the same port of each selected Node in the cluster using NAT. Makes a Service accessible from outside the cluster using :.	Creates an external load balancer in the current cloud (if supported) and assigns a fixed, external IP to the Service.	Exposes the Service using an arbitrary name (specified by externalName in the spec) by returning a CNAME record with the name.

Kubernetes ReplicaSet

https://kubernetes.io/docs/concepts/workloads/controllers/replicaset/

Kubernetes Labels and Selectors

https://kubernetes.io/docs/concepts/overview/working-with-objects/labels/

Kubernetes Manifest

Manifests are a way to declaratively define our microservice.

Kubectl

Kubectl uses the Kubernetes API to interact with the cluster

$ kubectl get - list resources
$ kubectl describe - show detailed information about a resource
$ kubectl logs - print the logs from a container in a pod
$ kubectl exec - execute a command on a container in a pod

Kubernetes Scaling

When traffic increases, we will need to scale the application to keep up with user demand.

Scaling is accomplished by changing the number of replicas in a Deployment

References

https://kubernetes.io/docs/tutorials/ https://kubernetes.io/docs/tutorials/kubernetes-basics/scale/scale-intro/

Kubernetes Configuration (YAML Cheats)

every configuration consists of 3 different parts:
- metadata
- specification (specs) DESIRED STATE
- status (automatically generated by k8s)Actual State
  - k8s maintains status from the kubernetes master etcd

K8s

Containers and Kubernetes

Containers

Kubernetes

Kubernetes - PODS

Kubernetes - Replication Controllers

Kubernetes services

Kubernetes - Volumes

Kubernetes - Namespace

What is namespace?

Namespaces

Minikube

Kubernetes

Nodes

Kubernetes - HELM

Helm Packages (Charts)

Best Practices

Namespaces

Kubernetes Concepts

What is Kubernetes?

What are Kubernetes Clusters?

Masters

Node

Kubernetes Deployment (Application Management)

Deployment Controller

Self Healing Mechanism

Pods

Kubernetes Services

Kubernetes ReplicaSet

Kubernetes Labels and Selectors

Kubernetes Manifest

Kubectl

Kubernetes Scaling

References

Kubernetes Configuration (YAML Cheats)

Persistent Volumes

Why PV?

Storage Infrastructure

Persistent Volume (PV)

Persistent Volume Claim (PVC)

Access modes

Lifecycle of PV

Static PV

Dynamic PV

Binding

We cannot bind two pvc’s to a single pv

However, we can bind pods to same pvc

PVC is binded to either PV or StorageClass

Secret ConfigMaps

References:

Further Reading

Explore CI/CD

Explore Ansible

Kubectl