kelseyhightower Kubernetes The Hard Way


CFSSL consists of:
  • a set of packages useful for building custom TLS PKI tools
  • the cfssl program, which is the canonical command line utility using the CFSSL packages.
  • the multirootca program, which is a certificate authority server that can use multiple signing keys.
  • the mkbundle program is used to build certificate pool bundles.
  • the cfssljson program, which takes the JSON output from the cfssl and multirootca programs and writes certificates, keys, CSRs, and bundles to disk.
The cfssl command line tool takes a command to specify what operation it should carry out:
   sign             signs a certificate
   bundle           build a certificate bundle
   genkey           generate a private key and a certificate request
   gencert          generate a private key and a certificate
   serve            start the API server
   version          prints out the current version
   selfsign         generates a self-signed certificate
   print-defaults   print default configurations
Use cfssl [command] -help to find out more about a command. The version command takes no arguments.
Networking
gcloud compute networks : kubernetes-the-hard-way
gcloud compute networks subnets : 10.240.0.0/24
gcloud compute firewall-rules
1. tcp, udp, icmp : source-ranges 10.240.0.0/24,10.200.0.0/16
2. tcp:22,tcp:6443,icmp : source-ranges 0.0.0.0/0
gcloud compute firewall-rules list
Now, create public address
gcloud compute addresses
Compute
3 K8s controllers: 
controller-0: 10.240.0.10
controller-1: 10.240.0.11
controller-2: 10.240.0.12
POD CIDR : 10.200.0.0/16
3 Worker node
worker-0: 10.240.0.20 pod-cidr 10.200.0.0/24
worker-1: 10.240.0.21 pod-cidr 10.200.1.0/24
worker-2: 10.240.0.22 pod-cidr 10.200.2.0/24
TLS Certificates
TLS certificates for the following components: 
* etcd, 
* kube-apiserver, 
* kube-controller-manager, 
* kube-scheduler, 
* kubelet, and 
* kube-proxy.
A public key infrastructure (PKI) is a set of roles, policies, hardware, software and procedures needed to create, manage, distribute, use, store and revoke digital certificates and manage public-key encryption. In cryptography, a PKI is an arrangement that binds public keys with respective identities of entities (like people and organizations).
Generate
1. ca.config file
Usage: 
"signing", 
"key encipherment", 
"server auth", 
"client auth"
2. Generate CSR JSON file
Output: Private key and Certificate for CA
3. Generate various CSR JSON files. Use CA key, CA key certificate, CA config file. 
Output Private key and Certificate 
3.1. Admin
3.2. for each worker node for kubelet. 
3.3  for kube-controller-manager
3.4 kube-proxy
3.5 kube-scheduler
4. Generate K8s API server certificate. 
For -hostname argument pass
KUBERNETES_HOSTNAMES=kubernetes,kubernetes.default,kubernetes.default.svc,kubernetes.default.svc.cluster,kubernetes.svc.cluster.local, K8s master node public IP, K8s all master nodes' private IP addresses. 
5. Generate Service Account pair
scp
6. To Worker node copy (scp) the following files
ca.pem
worker-N-key.pem
worker-N.pem
7. To all master node, copy (scp) following files
ca.pem
ca-key.pm
kubernetes.pm
kubernetes-key.pm
service-account.pm
service-account-key.pm
client authentication configuration
The kube-proxy, kube-controller-manager, kube-scheduler, and kubelet client certificates will be used to generate client authentication configuration file, also known as kubeconfigs. It enables Kubernetes clients to locate and authenticate to the Kubernetes API Servers.
Node authorization is a special-purpose authorization mode that specifically authorizes API requests made by kubelets. https://kubernetes.io/docs/reference/access-authn-authz/node/
1. Generate kubeconfig file for each worker node, with user name as system:node:workerN. The output is worker-N.kubeconfig
2. Generate kubeconfig file for the kube-proxy service. The output is kube-proxy.kubeconfig
3. Generate a kubeconfig file for the kube-controller-manager service. here server is 127.0.0.1 and output is kube-controller-manager.kubeconfig
4. Generate a kubeconfig file for the kube-scheduler service. here server is 127.0.0.1 and output is kube-scheduler.kubeconfig
5. Generate a kubeconfig file for the admin user. here server is 127.0.0.1 and output is admin.kubeconfig
To generate .kubeconfig file, we will use these three commands:
kubectl config set-cluster
kubectl config set-credentials
kubectl config set-context
Files for worker nodes:
  • worker-N.kubeconfig
  • kube-proxy.kubeconfig

Files for master nodes
  • admin.kubeconfig 
  • kube-controller-manager.kubeconfig 
  • kube-scheduler.kubeconfig

Data Encryption Config and Key
1. Generate encryption key with command
head -c 32 /dev/urandom | base64
2. Generate encryption-config.yaml file using that encryption key. 
Upload it on all three master node. 
Bootstrap etcd
On each master node
1. download and install etcd
2. copy these 3 files at /etc/etcd
ca.pem 
kubernetes-key.pem 
kubernetes.pem
3. Create /etc/systemd/system/etcd.service file. It opesn 2379 and 2380 port for etcd
4. Start etcd service
Bootstrap k8s-controller, K8s API server, K8s Scheduler 
On each master node
1. download and install 
kube-apiserver
kube-controller-manager
kube-scheduler
kubectl
2. Move all binary to /usr/local/bin
3. Move the following files to /var/lib/kubernetes/
ca.pem ca-key.pem kubernetes-key.pem kubernetes.pem service-account-key.pem service-account.pem   encryption-config.yaml
kube-controller-manager.kubeconfig
kube-scheduler.kubeconfig 
4. Create .service file for each of them at /etc/systemd/system/
For API server specify etcd and other parameters
  --service-cluster-ip-range=10.32.0.0/24 \\
  --service-node-port-range=30000-32767 \\
We can configure nginx for healthcheck of any service. Copy kubernetes.default.svc.cluster.local file at /etc/nginx/sites-available/
server {
  listen      80;
  server_name kubernetes.default.svc.cluster.local;
  location /healthz {
     proxy_pass                    https://127.0.0.1:6443/healthz;
     proxy_ssl_trusted_certificate /var/lib/kubernetes/ca.pem;
  }
}
RBAC for Kubelet Authorization
Let's set the Kubelet --authorization-mode flag to Webhook. Webhook mode uses the SubjectAccessReview API to determine authorization.
1. Create the system:kube-apiserver-to-kubelet ClusterRole with permissions to access the Kubelet API and perform most common tasks associated with managing pods:
2. Bind the system:kube-apiserver-to-kubelet ClusterRole to the kubernetes user:
It is sufficient to run on any one worker with kubectl
K8s Frontend LoadBalancer
Bootstrapping the Kubernetes Worker Nodes
1. First install
socat conntrack ipset
The socat binary enables support for the kubectl port-forward command.
2. Turn off swap
sudo swapoff -a
3. download and install 
critools (cri-ctl)
runc, container networking plugins, containerd, kubelet, and kube-proxy.
4. Installation directory 
  /etc/cni/net.d \
  /opt/cni/bin \
  /var/lib/kubelet \
  /var/lib/kube-proxy \
  /var/lib/kubernetes \
  /var/run/kubernetes
5. Create network configuration file at /etc/cni/net.d/
10-bridge.conf
99-loopback.conf
6. configure containerd service
7. configure Kubelet
8. configure kube-proxy
9. Start services: containerd kubelet kube-proxy
Configuring kubectl for Remote Access
Use the following commands
kubectl config set-cluster  // --certificate-authority=ca.pem
kubectl config set-credentials // --client-certificate=admin.pem  --client-key=admin-key.pem
kubectl config set-context // --user=admin
kubectl config use-context 
Provisioning Pod Network Routes
Add route for pods CIDR on each node, with destination as node's IP address. 
Deploying the DNS Cluster Add-on
https://storage.googleapis.com/kubernetes-the-hard-way/coredns.yaml

CKAD: Tips


1. how to run on master node?
nodeName: master

2. how to run command and args
commands: ["/bin/sh", "-c" "COMMAND"]

3. rolling update
Rolling update YAML
  strategy:
        type: RollingUpdate
        rollingUpdate:
           maxSurge: 1
           maxUnavailable: 1

4. inside container
volumeMounts:
     - mountPath: 

5. Useful command
k explain pods --recursive

6. Environment Variable

env: 
- name: ENV_NAME
  valueFrom: 
    configMapKeyRef:
      name: CM
      key: KEY 
- name: ENV_NAME
  value: "VALUE"


envFrom:
      - configMapRef:
          name: CM_NAME

Same applies for secret

7. Empty Dir volume

volumes: 
- name: VOL
  emptyDir: {}

8. Ports inside container

ports:
- containerPort: AAAA

9. CPU limit

resources:
  requests:
    cpu: "0.2"

10. PVC at Pod

volumes:
        - name: V_NAME
          persistentVolumeClaim:

            claimName: PVC_NAME

11. 

A. Security Context for container 

    securityContext:
      capabilities:
        add:
        - SYS_TIME
        drop: 
        - SYS_TIME

    securityContext:
    runAsUser: UID
    runAsGroup: GID
    fsGroup: NA
    fsGroupChangePolicy: NA
    allowPrivilegeEscalation : true | false
    privileged: true | false

B. Security Context for pod

    securityContext:
      systls: 
        - name: NAME
          value: VALUE

12. Ingress

spec:
  rules:
  - host: HOST_URL
    http:
      paths:
      - path: /PATH
        backend:
          serviceName: K8S_SVC
          servicePort: PORT(note NODE_PORT)



For testing HOST_URL can be specified with -H option

curl -H "HOST_URL" http://IP_ADDRESS/PATH 

13. PV

persistentVolumeReclaimPolicy: Retain | Recycle | Delete

14. netpol
Please define port also of service

  podSelector:
    matchLabels:
      KEY: VALUE
  policyTypes:
  - Ingress
  - Egress
  ingress:
  - from:
    - ipBlock:
        cidr: 172.17.0.0/16
        except:
        - 172.17.1.0/24
    - namespaceSelector:
        matchLabels:
          KEY: VALUE
    - podSelector:
        matchLabels:
          KEY: VALUE

Same for egress, we shall use to

15 Job

activeDeadlineSeconds
completions
parallelism
restartPolicy : {Never | OnFailure }  
Default is Always. Default is not suitable for Job
backoffLimit
ttlSecondsAfterFinished default 'never'


16 Probe

A livenessProbe
B readinessProbe
C startupProbe



exec:
  command: 
    - COMMAND1
    - COMMAND2

B

      httpGet:
        path: /PATH
        port: PORT
        httpHeaders:
        - name: Custom-Header
          value: VALUE

C

      tcpSocket:
        port: PORT

For all:

      initialDelaySeconds: 15
      periodSeconds: 20
      failureThreshold

11. k explain K8S_OBJECT --recursive

12. Rolling Update

  strategy:
    rollingUpdate:
      maxSurge: 1
      maxUnavailable: 1

    type: RollingUpdate

13. Volumes at pod using secret and configmap

volumes:
  name: VOLUME_NAME
  configMap:
    name: CM_NAME

volume:
  name: VOLUME_NAME
  secret:
    secretName: S_NAME

14. For 'k create' commnad, first we shall specify name of K8s object and then other parameter. the exception is svc. For svc, first specify type of svc and then its name and then other parameters. 

15. Inside YAML file, all type/parameter with plural name are list. E.g .volumes, volumemounts, containers, resources etc. Only exception is command. It is singular, yet list. However args is plural, no exception. 

16. Find API version with command

k explain OBJECT --recursive | grep VERSION

17. compare to 

k get po POD_NAME -o yaml 

below command is better

k get po POD_NAME -o yaml --export


18. To change namespace

k config set-context --current --namespace=NAMESPACE


StatefulSet


Purpose

1. creation order is guaranteed unless podManagementPolicy: parallel
2. pod name remain same even after restart
3. Use volumeClaimTemplate . Its an array. The content of array element is same as PVC. Each pod will get its own PV.

Headeless service will add DNS entries
- for each pod: "pod name"."headless service name"."namespace name".svc.cluster.local
Here pod IP address is not used.
- for headeless service: DNS is mapped to all pod's DNS. 

To create Headless service, specify ClusterIP: None

1. Headless service with deployment. 
Pod shall have value for subdomain as same as name of headless service.
Also specify hostname then only pod's dns name A record will be created. But all pod will have same hostname

2. To create Headless service with statefulset, no need to specify (1) subdomain (2) hostname
Instead of subdomain, we shall specify serviceName