medium_Kubernetes_Apprentice_Cookbook

00_concepts_abstraction_table.md

Abstraction Layer	Physical Layer	Uses Namespace	Description
Pod	Container	✅	A Pod is the minimal work unit of Kubernetes, it is generally equivalent to one applicative container but it can be composed of multiple ones.
Replicaset	Load Balancing	✅	A ReplicaSet keeps track of and maintain the amount of instances expected and running for a given pod.
Deployment	-	✅	A Deployment keeps track of and maintain the required configuration for a pod and replicaset.
StatefulSet	-	✅	A StatefulSet is a Deployment with insurance on the start order and volume binding, to keep state consistent in time.
Node	Host	❌	A Node can be a physical or virtual machine that is ready to host pods.
Service	Network	✅	A Service will define an entrypoint to a set of pods semantically tied together.
Ingress	Reverse Proxy	✅	An Ingress publishes Services outside the Cluster.
Cluster	Datacenter	❌	A Cluster is the set of available nodes, including the Kubernetes controllers.
Namespace	-	➖	A Namespace defines an isolated pseudo cluster in the current cluster.
StorageClass	Disk	❌	A StorageClass configures filesystems sources that can be used to dynamically create PersistentVolumes.
PersistentVolume	Disk Partition	❌	A PersistentVolume describe any kind of filesystem ready to be mounted on a pod.
PersistentVolumeClaim	-	✅	A PersistentVolumeClaim binds a PersistentVolume to a pod, which can then actively use it while running.
ConfigMap	Environment Variables	✅	A ConfigMap defines widely accessible properties.
Secret	Secured Env. Var.	✅	A Secret defines widely accessible properties with potential encryption and access limitations.

01_file_root_entities_table.md

Field	File type	Content
apiVersion	All files	Version to use while parsing the file.
kind	All files	Type of resource that the file is describing.
metadata	All files	Resource identification and labeling.
data	Data centric files (Secret, ConfigMap)	Content entry point for data mapping.
spec	Most files (Pod, Deployment, Ingress, ...)	Content entry point for resource configuration.

02_metadata_and_labels.yaml

# <metadata> narrows down selection and identify the resource
metadata:
  # The <name> entry is required and used to identify the resource
  name: my-resource
  namespace: my-namespace-or-default
  # <labels> is optional but often needed for resource selection
  labels:
    app: application-name
    category: back
  # <annotations> is optional and not needed for the configuration of Kubernetes
  annotations:
    version: 4.2

03_data_centric_file.yaml

apiVersion: v1
# <kind> defines the resource described in this file
kind: ConfigMap
metadata:
  name: my-config
data:
  # <data> configures data to load
  configuration_key: "configuration_value"
  properties_entry: |
    # Any multiline content is accepted
    multiline_config=true

04_infra_centric_file.yaml

apiVersion: v1
# <kind> defines the resource described in this file
kind: Pod
metadata:
  name: my-web-server
spec:
  # <spec> is a domain specific description of the resource.
  # The specification entries will be very different from one kind to another

05_secret.yaml

apiVersion: v1
kind: Secret
metadata:
  name: simple-web-secrets
# Opaque <type> can hold generic secrets, so no validation will be done.
type: Opaque
data:
  # Secrets should be encoded in base64
  secret_configuration_key: "c2VjcmV0IHZhbHVl"

06_secret_selector.yaml

valueFrom:
  secretKeyRef:
    name: simple-web-secrets
    key: secret_configuration_key

07_configmap.yaml

apiVersion: v1
kind: ConfigMap
metadata:
  name: simple-web-config
  namespace: default
data:
  configuration_key: "Configuration value"

08_configmap_selector.yaml

valueFrom:
  configMapKeyRef:
    name: simple-web-config
    key: configuration_key

09_pod.yaml

apiVersion: v1
kind: Pod
metadata:
  name: my-web-server
spec:
  # <containers> is a list of container definition to embed in the pod
  containers:
    - name: web
      image: nginx
      ports:
        - name: web
          containerPort: 80
          protocol: TCP
      env:
        - name: SOME_CONFIG
          # Create a line "value: <config_entry>" from the ConfigMap data
          valueFrom:
            configMapKeyRef:
              name: simple-web-config
              key: configuration_key
        - name: SOME_SECRET
          # Create a line "value: <config_entry>" from the Secret data
          valueFrom:
            secretKeyRef:
              name: simple-web-secrets
              key: secret_configuration_key

10_deployment.yaml

apiVersion: apps/v1
kind: Deployment
metadata:
  name: my-web-server-deployment
  namespace: default
  labels:
    app: webserver
spec:
  # <selector> should retrieve the Pod defined below, and possibly more
  selector:
    matchLabels:
      app: webserver
      instance: nginx-ws-deployment
  # <replicas> asks for 3 pods running in parallel at all time
  replicas: 3
  # The content of <template> is a Pod definition file, without <apiVersion> nor <kind>
  template:
    metadata:
      name: my-web-server
      namespace: default
      labels:
        app: webserver
        instance: nginx-ws-deployment
    spec:
      containers:
        - name: web
          image: nginx
          ports:
            - name: web
              containerPort: 80
              protocol: TCP
          env:
            - name: SOME_CONFIG
              # Create a line "value: <config_entry>" from the ConfigMap data
              valueFrom:
                configMapKeyRef:
                  name: simple-web-config
                  key: configuration_key
            - name: SOME_SECRET
              # Create a line "value: <config_entry>" from the Secret data
              valueFrom:
                secretKeyRef:
                  name: simple-web-secrets
                  key: secret_configuration_key

11_service.yaml

apiVersion: v1
kind: Service
metadata:
  name: simple-web-service-clusterip
spec:
  # ClusterIP is the default service <type>
  type: ClusterIP
  # Select all pods declaring a <label> entry "app: webserver"
  selector:
    app: webserver
  ports:
    - name: http
      protocol: TCP
      # <port> is the port to bind on the service side
      port: 80
      # <targetPort> is the port to bind on the Pod side
      targetPort: 80

12_ingress.yaml

apiVersion: networking.k8s.io/v1
kind: Ingress
metadata:
  name: simple-web-ingress
  annotations:
    nginx.ingress.kubernetes.io/rewrite-target: /
spec:
  rules:
    # Using <host> redirects all request matching the given DNS name to this rule
    - host: "*.minikube.internal"
      http:
        paths:
          - path: /welcome
            pathType: Prefix
            backend:
              service:
                name: simple-web-service-clusterip
                port:
                  number: 80
    # All other requests will be redirected through this rule
    - http:
        paths:
          - path: /
            pathType: Prefix
            backend:
              service:
                name: simple-web-service-clusterip
                port:
                  number: 80

13_create_resource.sh

# <kind> is the type of resource to create (e.g. deployment, secret, namespace, quota, ...)
$ kubectl create <kind> <name>
$ kubectl edit   <kind> <name>
$ kubectl delete <kind> <name>

# All those commands can be used through a description file.
$ kubectl create -f <resource>.yaml
$ kubectl edit   -f <resource>.yaml
$ kubectl delete -f <resource>.yaml

14_create_resource_from_file.sh

# Create and update any resource
$ kubectl apply   -f <resource>.yaml
# Delete any resource
$ kubectl delete  -f <resource>.yaml

15_kubectl_get.sh

# Fetch everything
$ kubectl get all
NAME                                            READY   STATUS    RESTARTS   AGE
pod/my-web-server-deployment-58c4fd887f-5vm2b   1/1     Running   0          128m
pod/my-web-server-deployment-58c4fd887f-gq6lr   1/1     Running   0          128m
pod/my-web-server-deployment-58c4fd887f-gs6qb   1/1     Running   0          128m

NAME                                   TYPE           CLUSTER-IP       EXTERNAL-IP   PORT(S)                      AGE
service/simple-web-service-clusterip   ClusterIP      10.96.96.241     <none>        80/TCP,443/TCP               60m
service/simple-web-service-lb          LoadBalancer   10.108.182.232   <pending>     80:31095/TCP,443:31940/TCP   60m
service/simple-web-service-np          NodePort       10.101.77.203    <none>        80:31899/TCP,443:31522/TCP   60m

NAME                                       READY   UP-TO-DATE   AVAILABLE   AGE
deployment.apps/my-web-server-deployment   3/3     3            3           136m

NAME                                                  DESIRED   CURRENT   READY   AGE
replicaset.apps/my-web-server-deployment-58c4fd887f   3         3         3       128m

# We can ask for more details
$ kubectl get deployment -o wide
NAME                       READY   UP-TO-DATE   AVAILABLE   AGE    CONTAINERS   IMAGES  SELECTOR
my-web-server-deployment   3/3     3            3           121m   web          nginx   app=webserver

# Some resources are not visible using "all" but available
$ kubectl get configmap
NAME                DATA   AGE
kube-root-ca.crt    1      38d
simple-web-config   3      3h17m

16_kubectl_describe.sh

# Let's describe the ingress for the sake of example
$ kubectl describe ingress/simple-web-ingress
Name:             simple-web-ingress
Namespace:        default
Address:          192.168.64.2
Default backend:  default-http-backend:80 (<error: endpoints "default-http-backend" not found>)
Rules:
  Host                 Path  Backends
  ----                 ----  --------
  *.minikube.internal
                       /welcome   simple-web-service-clusterip:80 (172.17.0.4:80,172.17.0.5:80,172.17.0.6:80 + 1 more...)
  *
                       /   simple-web-service-clusterip:80 (172.17.0.4:80,172.17.0.5:80,172.17.0.6:80 + 1 more...)
Annotations:           nginx.ingress.kubernetes.io/rewrite-target: /
Events:
  Type    Reason  Age                 From                      Message
  ----    ------  ----                ----                      -------
  Normal  UPDATE  7m6s (x6 over 23h)  nginx-ingress-controller  Ingress default/simple-web-ingress

17_kubectl_log.sh

$ kubectl logs deployments/my-web-server-deployment
Found 3 pods, using pod/my-web-server-deployment-755b499f77-4n5vn
# [logs]

18_kubectl_exec.sh

# As for logs, when called on any resource enclosing Pods,
# Kubernetes will randomly chose one to  execute the action
$ kubectl exec -it deployment/my-web-server-deployment -- /bin/bash
root@my-web-server-deployment-56c4554cf9-qwtm6:/# ls
# [...]

19_appendix_docker_kube.md

Operation	Docker	Kubernetes
Running containers	docker ps	kubectl get pods
Configuration details	docker inspect <name>	kubectl describe <name>
Show logs	docker logs <name>	kubectl logs <name>
Enter container	docker exec -it <name> /bin/bash	kubectl exec -it <name> -- /bin/bash