K8s Dashboard


CKAD : 4.Design


Each component should be decoupled from resources.

All resources have transient relationship with others.

K8s orchestration works with series of agents = controllers = watch loops.

PodSpec determines the best node for deployment

One CPU =
1 AWS vCPU or
1 GCP Core
1 Azure vCore
1 Hyperthread in bare metal Intel CPU with Hyperthreading

Label and Selector 

Label can be
- production / development
- department name
- team name
- primary application developer

Selectors are namespace scoped, unless --all-namespace is used
--selector key=value
OR
-l key=value

If we use command
kubectl create deployment design2 --image=nginx
Then a pod is created with label app=design2
if we edit label of that pod, then design2 deployment will create another pod with label app=design2
if we delete deployment design2 then all pod whose label is app=design2, those will only get deleted. 

To show all labels use --show-labels options with kubectl get command. 

Job

Job is for scenarios when you don’t want the process to keep running indefinitely.  

It does support parallel processing of a set of independent but related work items. These might be 
- emails to be sent, 
- frames to be rendered, 
- files to be transcoded, 
- ranges of keys in a NoSQL database to scan, and so on.

A Replication Controller manages Pods which are not expected to terminate (e.g. web servers), and a Job manages Pods that are expected to terminate (e.g. batch tasks).

Jobs are part of batch API group
It has following parameters
1. activeDeadlineSeconds it can remain alive for that many seconds only.
2. completions : How many instance ? default 1
3. parallelism : how many should run at a time ? default 1. with value 0, the job is paused. 
4. restartPolicy : {Never | OnFailure } Default is Always. Default is not suitable for Job
5. It is restarted for backoffLimit times default 6
6. ttlSecondsAfterFinished default 'never'

* If parallelism > completions  then parallelism = completions 

While debugging set restartpolicy = never. This policy applies to pod not to job

The job status is Failed if
- restarted more than backoffLimit times OR
- it run more than activeDeadlineSeconds
else status is Complete

Delete Job
With cascade = false, only job get deleted, not pods

kubectl delete jobs job_name cascade=false

CronJob
Linux style cronjob syntax
MM HH DD MM WW
It can be list with comma separated value: 1,2
It can be range with hyphen: 1-5
It can be * to indicate all
It can be */ and number to indicate periodic: */2
* and ? has same meaning. 

CronJob creates multiple jobs as per schedule. The CronJob is only responsible for creating Jobs that match its schedule, and the Job in turn is responsible for the management of the Pods it represents.

It has following parameters1. If a cronJob has sleep for 30 seconds and activeDeadlineSeconds is 10 then none of the job created by cronJob get completed state. 

2. startingDeadlineSeconds If cornjob cannot scheduled within this time then it is considered as failed. Failure can also because of forbid policy. After 100 such failure, no more job will get scheduled. 

Note: If startingDeadlineSeconds is set then failure count is considered in last startingDeadlineSeconds . It should be less then 100. 

3. concurrencyPolicy 
Allow:
Forbid: If second job is scheduled, before earlier job finished, then it is not allowed
Replace

4. suspend
all subsequent job will not be scheduled. 

5. successfulJobsHistoryLimit and failedJobsHistoryLimit
How many job shall be kept


Terms for multi container pod
1. Ambassador : Communicate with outside resources / outside cluster. E.g. Envoy Proxy
- Proxy local connection
- Reverse Proxy
- Limits HTTP request
- Re-route to outside world
2. Adapter : Modify data that primary container generates
3. sidecar : helps to provide service that is not found in primary container. E.g. logging

Flexibility : one application per pod
granular scalability : one application per pod
best inter container performance : Multiple application per pod

Containerizing an application

- It should be stateless
- It should be transient
- Remove the environment configuration. It should be via ConfigMap and Secrets
- it is like converting city bus to scooters 

After containerization of application, just ask

Q1 : Is my application as decoupled as it could possible be?
Q2 : Are all components design considering other components are transient. Will it work with Chaos Monkey?
Q3 : Can I scale any particular component?
Q4 : Have I used stable and open standard to meet my need?

Managing Resource Usage

If pod ask more CPU then defined, then
- Nothing

If pod ask more memory then defined, then behavior is undefined
- restart pod OR
- evicted node

If pod ask memory more than node has, then
- evicted node

If pod ask more storage then defined, then 
- evicted node

Resource Limits

1. CPU: cpu
2. Memory: memory
3. Huge Pages: hugepages-2Mi
4. Ephemeral Storage: ephemeral-storage
they apply at container level
Pod level value is summation of all container's values

The resources can be specify at project quota level also. 

limits:
  cpu: "1"
  memory: "1Gi"
requests:
  cpu: "0.5"
  memory: "500Mi"

k describe node "Node Name"

We can specify LimitRange object with default values. It is applicable within namespace. It is applicable if admission controller LimitRanger is enabled. 

apiVersion: v1
kind: LimitRange
metadata:
  name: limit-mem-cpu-per-container
spec:
  limits:
  - max:
      cpu: "800m"
      memory: "1Gi"
    min:
      cpu: "100m"
      memory: "99Mi"
    default:
      cpu: "700m"
      memory: "900Mi"
    defaultRequest:
      cpu: "110m"
      memory: "111Mi"
    type: Container

- While creating container, if memory request and limit both are not specified 
then default range applies.  
- While creating container, if memory request is not specified and limit is specified. Then request value is same as limit
- While creating container, if memory request is specified and limit is not specified. Then limit value is double then request value


CNI 

* Some CNI plugins supports Network Policies. E.g. Calico, Canal, Kube Router, Romana, Weave Net

* Some CNI plugins supports encryption of UDP and TCP traffic. E.g. Calico, Kopeio, Weave Net

* Some CNI plugins allows vxlan. E.g. Canal, Flannel, Kopeio-networking, Weave Net

* CNI plugins are layer 2 or layer 3
Layer 2: Canal, Flannel, Kopeio-networking, Weave Net
Layer 3: Calico, Romana, Kube Router

* kubenet is basic CNI. It relis on cloud provider for routing and cross node networking

./enter_pod.sh "pod name"


#!/bin/sh

containerId=`kubectl get pods $1 -o jsonpath='{.status.containerStatuses[1].containerID}' | sed -e "s/^docker:\/\///"`
pid=`docker inspect --format {{.State.Pid}} $containerId`
echo $pid
sudo nsenter --target $pid --mount --uts --ipc --net --pid sh

CKAD : 3. Build


App Container (appc) is an open specification that defines several aspects of how to run applications in containers: an image format, runtime environment, and discovery protocol. rkt's native image format and runtime environment are those defined by the specification.

clear container (from intel) uses kvmtool mini-hypervisor. So it is VM with quick bootup and low memory footprint. Not comparable with Docker but acceptable for many use cases. 

If we create a file inside Docker container, then it is acutally located at 
/var/snap/docker/common/var-lib-docker/aufs/diff/  
OR 
/var/lib/docker/aufs/diff/

Tools
1. Docker
2. buildah
- create OCI image
- with or without Dockerfile
- no superuser previliage needed
- Go-lan based API for easy integation
3. podman (pod manager)
- replacement of "docker run"
- it is for container LCM
4. Kompose

sudo kompose convert -f docker-compose.yaml -o localregistry.yaml

latest is just a string. we need process to name and rename latest version as "laters" as an when it available. Else, there is no point. 

k exec -it -- /bin/bash
Here instead of /bin/bash any tool of local host, (where kubectl is running) can be used. 

redinessProbe and livenessProbe
1. exec statement
2. HTTP GET. return value 200-399
3. TCP. Try to open port on pre-determined port

To get logs generated by etcd
k -n kube-system logs etcd

The events can be listed with
k describe pod  

We can user "--dry-run -o yaml" just to generate YAML file

Minikube

To access K8s service on Minikube we have few approaches

1. Make it as NodePort Service

1.1  we can change service type as NodePort by
k path svc -p '{"spec":{"type":"NodePort"}}'
Now to access NodePort service on Minikube, we need IP address of virtual box. 

1.2
minikube ip
this command  give IP address of Worker+Master Node.
User command 
curl http://192.168.99.108:31754/v2/
curl http://"Minikube IP":"NodePort"/v2/

1.3

Use the command
minikube service --url
you will get service end point
http://192.168.99.108:31754

http://"Minikube IP":"NodePort"

We can open this URL using default browser using command
minikube service 

2.1

We can use ClusterIP

sudo route add 10.100.88.2 gw 192.168.99.108
sudo route add gw

Registry

We should add insecure registry to docker with its ClusterIP 

sudo vim /etc/docker/daemon.json

{ "insecure-registries":["10.110.186.162:5000"] }

Then Restart Docker Service
sudo systemctl restart docker.service

CKAD : 2. K8s Architecture


Key take away points
  • All the configuration is defined in YAML and stored in JSON format
  • Container creation tools: Buildah, Podman, cri-o, containerd, frakti, 
  • Mesos has multi level scheduler for data center cluster
  • Evolution: Brog-> Mesos, Cloud Foundry, K8s, Omega
  • Replication Controller is now
  • - Deployment controller
  • - Replicaset
  • Deployment ensures that resources are available such as (1) IP Address and (2) Storage. Then deploys ReplicaSet
  • So if we delete ReplicaSet then deployment recreate it. 
  • If we delete deployment, then ReplicSet also get deleted. But service and pod remains
  • If we delete service then pod get delted. 
  • Node has taints to discourage pod assignment, unless pod has toleration taint is expressed as key=value:effect
  • Annotation is not for k8s. it is for 3rd party tools
  • 'Cloud controller manager' is optional at master node. If it is present, the kublet shall be started with option --cloud-provider-external
  • Pause container is used to get IP address
Useful commands
1. 1 To run pod, without YAML filek run newpod --image=nginx --generator=run-pod/v1

1.2 To create deployment without YAML filek create deployment firstpod --image=nginx

2. To know all taintsk describe nodes | grep -i taint

3.1 To know about all resourcesk api-resources
NAME                              SHORTNAMES       APIGROUP                       NAMESPACED   KIND
bindings                                                                          true         Binding
componentstatuses                 cs                                              false        ComponentStatus
configmaps                        cm                                              true         ConfigMap
endpoints                         ep                                              true         Endpoints
events                            ev                                              true         Event
limitranges                       limits                                          true         LimitRange
namespaces                        ns                                              false        Namespace
nodes                             no                                              false        Node
persistentvolumeclaims            pvc                                             true         PersistentVolumeClaim
persistentvolumes                 pv                                              false        PersistentVolume
pods                              po                                              true         Pod
podtemplates                                                                      true         PodTemplate
replicationcontrollers            rc                                              true         ReplicationController
resourcequotas                    quota                                           true         ResourceQuota
secrets                                                                           true         Secret
serviceaccounts                   sa                                              true         ServiceAccount
services                          svc                                             true         Service
mutatingwebhookconfigurations                      admissionregistration.k8s.io   false        MutatingWebhookConfiguration
validatingwebhookconfigurations                    admissionregistration.k8s.io   false        ValidatingWebhookConfiguration
customresourcedefinitions         crd,crds         apiextensions.k8s.io           false        CustomResourceDefinition
apiservices                                        apiregistration.k8s.io         false        APIService
controllerrevisions                                apps                           true         ControllerRevision
daemonsets                        ds               apps                           true         DaemonSet
deployments                       deploy           apps                           true         Deployment
replicasets                       rs               apps                           true         ReplicaSet
statefulsets                      sts              apps                           true         StatefulSet
tokenreviews                                       authentication.k8s.io          false        TokenReview
localsubjectaccessreviews                          authorization.k8s.io           true         LocalSubjectAccessReview
selfsubjectaccessreviews                           authorization.k8s.io           false        SelfSubjectAccessReview
selfsubjectrulesreviews                            authorization.k8s.io           false        SelfSubjectRulesReview
subjectaccessreviews                               authorization.k8s.io           false        SubjectAccessReview
horizontalpodautoscalers          hpa              autoscaling                    true         HorizontalPodAutoscaler
cronjobs                          cj               batch                          true         CronJob
jobs                                               batch                          true         Job
certificatesigningrequests        csr              certificates.k8s.io            false        CertificateSigningRequest
leases                                             coordination.k8s.io            true         Lease
events                            ev               events.k8s.io                  true         Event
daemonsets                        ds               extensions                     true         DaemonSet
deployments                       deploy           extensions                     true         Deployment
ingresses                         ing              extensions                     true         Ingress
networkpolicies                   netpol           extensions                     true         NetworkPolicy
podsecuritypolicies               psp              extensions                     false        PodSecurityPolicy
replicasets                       rs               extensions                     true         ReplicaSet
network-attachment-definitions    net-attach-def   k8s.cni.cncf.io                true         NetworkAttachmentDefinition
ingresses                         ing              networking.k8s.io              true         Ingress
networkpolicies                   netpol           networking.k8s.io              true         NetworkPolicy
runtimeclasses                                     node.k8s.io                    false        RuntimeClass
poddisruptionbudgets              pdb              policy                         true         PodDisruptionBudget
podsecuritypolicies               psp              policy                         false        PodSecurityPolicy
clusterrolebindings                                rbac.authorization.k8s.io      false        ClusterRoleBinding
clusterroles                                       rbac.authorization.k8s.io      false        ClusterRole
rolebindings                                       rbac.authorization.k8s.io      true         RoleBinding
roles                                              rbac.authorization.k8s.io      true         Role
priorityclasses                   pc               scheduling.k8s.io              false        PriorityClass
csidrivers                                         storage.k8s.io                 false        CSIDriver
csinodes                                           storage.k8s.io                 false        CSINode
storageclasses                    sc               storage.k8s.io                 false        StorageClass
volumeattachments                                  storage.k8s.io                 false        VolumeAttachment

3.2 We can list associated verbs with commandk api-resources -o wide

3.3 We can list multiple resources as comma separated list
kubectl get deploy,rs,po,svc,ep

4. Under container we write:
ports:
- containerPort: 80

5. Under Service we write:
ports:
 - protocol: TCP
   port: 80