An Introduction To Kubernetes ☸

My talk from EuroPython 2021

Transcript

1. @m_holtermann
   An Introduction To
   Kubernetes
   

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2. @m_holtermann
   What is Kubernetes?
   

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3. @m_holtermann
   Hi, I’m
   Markus Holtermann
   

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4. @m_holtermann
   Hi, I’m
   Markus Holtermann
   W
   e're
   hiring
   

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5. @m_holtermann
   A system to run containers
   

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6. @m_holtermann
   An API server you interact
   with using kubectl
   

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7. @m_holtermann
   Eventually consistent
   

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8. @m_holtermann
   @m_holtermann
   Cluster
   

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9. @m_holtermann
   @m_holtermann
   Cluster
   Node 1 Node 2 Node 3
   

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10. @m_holtermann
    @m_holtermann
    Cluster
    Node 1 Node 2 Node 3
    Pod Pod
    Pod Pod
    Pod Pod
    Pod Pod
    Pod Pod
    Pod Pod
    Pod
    

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11. @m_holtermann
    @m_holtermann
    Cluster
    Node 1 Node 2 Node 3
    Pod Pod
    Pod Pod
    Pod Pod
    Pod Pod
    Pod Pod
    Pod Pod
    Pod
    

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12. @m_holtermann
    @m_holtermann
    Cluster
    Node 1 Node 2 Node 3
    Pod
    Container
    Pod
    Container
    Container
    Pod
    Container
    Pod
    Container
    Pod
    Container
    Pod
    Container
    Pod
    Container
    Container
    Pod
    Container
    Container
    Pod
    Container
    Container
    Pod
    Container
    Container
    Pod
    Container
    Pod
    Container
    Pod
    Container
    

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13. @m_holtermann
    Concepts
    

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14. @m_holtermann
    Everything is a resource
    

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15. @m_holtermann
    Key attributes:
    kind, apiVersion, meta,
    spec
    

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16. @m_holtermann
    cluster-scoped or
    namespace-scoped
    

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17. @m_holtermann
    Building Blocks
    https://kubernetes.io/docs/reference/kubernetes-api/
    

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18. @m_holtermann
    Namespaces
    

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19. @m_holtermann
    @m_holtermann
    apiVersion: v1
    kind: Namespace
    metadata:
    name: myapp
    $ kubectl get namespaces
    NAME STATUS AGE
    default Active 32d
    kube-system Active 32d
    $ kubectl apply -f k8s-namespace.yaml
    namespace/myapp created
    $ kubectl get namespaces
    NAME STATUS AGE
    default Active 32d
    kube-system Active 32d
    myapp Active 5s
    

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20. @m_holtermann
    Pods
    

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21. @m_holtermann
    @m_holtermann
    apiVersion: v1
    kind: Pod
    metadata:
    name: whoami
    namespace: myapp
    labels:
    app.kubernetes.io/instance: whoami
    spec:
    containers:
    - image: traefik/whoami:latest
    name: whoami
    ports:
    - containerPort: 80
    name: http
    protocol: TCP
    $ kubectl -n myapp get pods
    No resources found in myapp namespace.
    $ kubectl apply -f k8s-pod.yaml
    pod/whoami created
    $ kubectl -n myapp get pods
    NAME READY STATUS RESTARTS AGE
    whoami 1/1 Running 0 8s
    

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22. @m_holtermann
    Services
    

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23. @m_holtermann
    @m_holtermann
    apiVersion: v1
    kind: Service
    metadata:
    name: whoami
    namespace: myapp
    spec:
    ports:
    - name: http
    port: 8080
    protocol: TCP
    targetPort: http
    selector:
    app.kubernetes.io/instance: whoami
    $ kubectl -n myapp get services
    No resources found in myapp namespace.
    $ kubectl apply -f k8s-service.yaml
    service/whoami created
    $ kubectl -n myapp get services
    NAME TYPE CLUSTER-IP PORT(S) AGE
    whoami ClusterIP 10.240.28.82 8080/TCP 2s
    

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24. @m_holtermann
    Ingresses
    

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25. @m_holtermann
    @m_holtermann
    apiVersion: networking.k8s.io/v1
    kind: Ingress
    metadata:
    name: whoami
    namespace: myapp
    spec:
    rules:
    - host: example.com
    http:
    paths:
    - path: /
    pathType: Prefix
    backend:
    service:
    name: whoami
    port:
    name: http
    $ kubectl -n myapp get ingress
    No resources found in myapp namespace.
    $ kubectl -n myapp apply -f k8s-ingress.yaml
    ingress.networking.k8s.io/whoami created
    $ kubectl -n myapp get ingress
    NAME HOSTS ADDRESS PORTS AGE
    whoami example.com 80 3s
    

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26. @m_holtermann
    Configmaps & Secrets
    

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27. @m_holtermann
    @m_holtermann
    apiVersion: v1
    kind: ConfigMap
    metadata:
    name: whoami
    namespace: myapp
    data:
    WHOAMI_NAME: "Darth Vader"
    $ kubectl -n myapp get configmaps
    No resources found in myapp namespace.
    $ kubectl -n myapp apply -f k8s-configmap.yaml
    configmap/whoami created
    $ kubectl -n myapp get configmaps
    NAME DATA AGE
    whoami 1 3s
    apiVersion: v1
    kind: Secret
    metadata:
    name: whoami
    namespace: myapp
    type: Opaque
    data:
    a-key: THVrZSwgSSdtIHlvdXIgZmF0aGVyIQo=
    $ kubectl -n myapp get secrets
    No resources found in myapp namespace.
    $ kubectl -n myapp apply -f k8s-secret.yaml
    secret/whoami created
    $ kubectl -n myapp get secrets
    NAME TYPE DATA AGE
    whoami Opaque 1 3s
    

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28. @m_holtermann
    Deployments
    

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29. @m_holtermann
    @m_holtermann
    apiVersion: apps/v1
    kind: Deployment
    ...
    spec:
    replicas: 3
    selector:
    matchLabels:
    app.kubernetes.io/instance: whoami
    template:
    metadata:
    labels:
    app.kubernetes.io/instance: whoami
    spec:
    containers:
    - image: traefik/whoami:latest
    name: whoami
    env:
    - name: SOME_SECRET
    valueFrom:
    secretKeyRef:
    name: whoami
    key: a-key
    envFrom:
    - configMapRef:
    name: whoami
    ports:
    - containerPort: 80
    name: http
    protocol: TCP
    $ kubectl -n myapp get deployments
    No resources found in myapp namespace.
    $ kubectl -n myapp apply -f k8s-deployment.yaml
    deployment.apps/whoami created
    $ kubectl -n myapp get deployments
    NAME READY UP-TO-DATE AVAILABLE AGE
    whoami 3/3 3 3 4s
    $ kubectl -n myapp get pods
    NAME READY STATUS RESTART AGE
    whoami 1/1 Running 0 10m
    Whoami-66bc5b-jtpjs 1/1 Running 0 23s
    whoami-66bc5b-pv7kv 1/1 Running 0 23s
    Whoami-66bc5b-sk2f8 1/1 Running 0 23s
    

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30. @m_holtermann
    Kubernetes & Django
    

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31. @m_holtermann
    @m_holtermann
    ---
    apiVersion: v1
    kind: ConfigMap
    metadata:
    name: myapp
    namespace: mynamespace
    data:
    ALLOWED_HOSTS: "myapp.com,myapp.mynamespace.svc.cluster.local
    "
    ---
    apiVersion: v1
    kind: Secret
    metadata:
    name: myapp
    namespace: mynamespace
    type: Opaque
    data:
    # postgres://user:pw@pgserver:5432/dbname
    DATABASE_URL: cG9zdGdyZXM6Ly91c2VyOnB3QHBnc2VydmVyOjU0MzIvZGJuYW1l=
    SECRET_KEY: KzVAYmpkbXhqd2koYjQoeHFrOWwkdCZidjB5QCF4bXpfI2k3PSVlKmhpdnUqdTdmXng=
    

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32. @m_holtermann
    @m_holtermann
    import os
    import dj_database_url
    SECRET_KEY = os.environ["SECRET_KEY"]
    DEBUG = os.getenv("DEBUG", "") == "true"
    ALLOWED_HOSTS = os.getenv("ALLOWED_HOSTS", "").split(",")
    DATABASES = {"default": dj_database_url.
    config()}
    

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33. @m_holtermann
    @m_holtermann
    apiVersion: apps/v1
    kind: Deployment
    metadata:
    name: myapp
    namespace: mynamespace
    spec:
    replicas: 2
    selector:
    matchLabels:
    app.kubernetes.io/name
    : myapp
    template:
    metadata:
    labels:
    app.kubernetes.io/name
    : myapp
    spec:
    containers:
    - envFrom:
    - configMapRef:
    name: myapp
    - secretRef:
    name: myapp
    image: path.to.my/docker/image:tag
    imagePullPolicy
    : IfNotPresent
    name: web
    ports:
    - containerPort: 8080
    name: http
    protocol: TCP
    restartPolicy: Always
    

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34. @m_holtermann
    @m_holtermann
    # Dockerfile
    # ...
    ENTRYPOINT ["/entrypoint.sh "]
    CMD ["gunicorn", "-b", ":8080", "-w", "4", "--log-level", "INFO",
    "--access-logfile ", "-", "--error-logfile ", "-", "myapp.wsgi"]
    # ...
    # /entrypoint.sh
    #!/bin/sh
    set -e
    cmd="$@"
    until django-admin dbshell -- --command '\q'; do
    >&2 echo "Postgres is unavailable - sleeping "
    sleep 5
    done
    django-admin migrate -v 2
    django-admin collectstatic -v 2 --no-input
    exec $cmd
    

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35. @m_holtermann
    This is Kubernetes!
    

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