Follow Kubernetes the Hard way

June 19, 2023

This article was written by just following Kelsey Hightower’s Kubernetes Hardway document to understand Kubernetes internal architecture.

Overview

Control plane

The control plane’s overview:

Control Plane

Each node on the control plane:

etcd: Store cluster states
- 2379: Client API port
- 2380: Peer API port
Kubernetes API Server
- 6443
Scheduler
Controller Manager
nginx
- For HTTP heath check from GCP Load Balancer

Each middleware was installed by systemd.

Data plane

Data Plane

containerd
- start from systemd
- container networking plugin
  - See this article or this article for the overview of CNI
  - bridge network configuration
kubelet
- start from systemd
kube-proxy
- start from systemd
- iptables mode
Coredns
- In kubernetes
CLIs
- runc
- crictl
- kubectl

Networking

Pod to Pod: Use iptables by kube-proxy.
- But I can’t find iptable rules to route traffic for a k8s service
Node to Node networking: Use VPC Routes

2. Client tools

brew install cfssl

> cfssl version
Version: 1.6.4
Runtime: go1.20.3
> cfssljson --version
Version: 1.6.4
Runtime: go1.20.3

3 Compute resources

Set up them by terraform. Change the compute resource names

from worker-$n to k8s-worker-$n
from controller-$n to k8s-controller-$n

4. Certificate authority

Certificate Authority

cat > ca-config.json <<EOF
{
  "signing": {
    "default": {
      "expiry": "8760h"
    },
    "profiles": {
      "kubernetes": {
        "usages": ["signing", "key encipherment", "server auth", "client auth"],
        "expiry": "8760h"
      }
    }
  }
}
EOF

cat > ca-csr.json <<EOF
{
  "CN": "Kubernetes",
  "key": {
    "algo": "rsa",
    "size": 2048
  },
  "names": [
    {
      "C": "US",
      "L": "Portland",
      "O": "Kubernetes",
      "OU": "CA",
      "ST": "Oregon"
    }
  ]
}
EOF

cfssl gencert -initca ca-csr.json | cfssljson -bare ca

The Admin Client Certificate

cat > admin-csr.json <<EOF
{
  "CN": "admin",
  "key": {
    "algo": "rsa",
    "size": 2048
  },
  "names": [
    {
      "C": "US",
      "L": "Portland",
      "O": "system:masters",
      "OU": "Kubernetes The Hard Way",
      "ST": "Oregon"
    }
  ]
}
EOF

cfssl gencert \
  -ca=ca.pem \
  -ca-key=ca-key.pem \
  -config=ca-config.json \
  -profile=kubernetes \
  admin-csr.json | cfssljson -bare admin

The Kubelet Client Certificates

for instance in k8s-worker-0 k8s-worker-1 k8s-worker-2; do
cat > ${instance}-csr.json <<EOF
{
  "CN": "system:node:${instance}",
  "key": {
    "algo": "rsa",
    "size": 2048
  },
  "names": [
    {
      "C": "US",
      "L": "Portland",
      "O": "system:nodes",
      "OU": "Kubernetes The Hard Way",
      "ST": "Oregon"
    }
  ]
}
EOF

EXTERNAL_IP=$(gcloud compute instances describe ${instance} \
  --format 'value(networkInterfaces[0].accessConfigs[0].natIP)')

INTERNAL_IP=$(gcloud compute instances describe ${instance} \
  --format 'value(networkInterfaces[0].networkIP)')

cfssl gencert \
  -ca=ca.pem \
  -ca-key=ca-key.pem \
  -config=ca-config.json \
  -hostname=${instance},${EXTERNAL_IP},${INTERNAL_IP} \
  -profile=kubernetes \
  ${instance}-csr.json | cfssljson -bare ${instance}
done

The Controller Manager Client Certificate

cat > kube-controller-manager-csr.json <<EOF
{
  "CN": "system:kube-controller-manager",
  "key": {
    "algo": "rsa",
    "size": 2048
  },
  "names": [
    {
      "C": "US",
      "L": "Portland",
      "O": "system:kube-controller-manager",
      "OU": "Kubernetes The Hard Way",
      "ST": "Oregon"
    }
  ]
}
EOF

cfssl gencert \
  -ca=ca.pem \
  -ca-key=ca-key.pem \
  -config=ca-config.json \
  -profile=kubernetes \
  kube-controller-manager-csr.json | cfssljson -bare kube-controller-manager

The Kube Proxy Client Certificate

cat > kube-proxy-csr.json <<EOF
{
  "CN": "system:kube-proxy",
  "key": {
    "algo": "rsa",
    "size": 2048
  },
  "names": [
    {
      "C": "US",
      "L": "Portland",
      "O": "system:node-proxier",
      "OU": "Kubernetes The Hard Way",
      "ST": "Oregon"
    }
  ]
}
EOF

cfssl gencert \
  -ca=ca.pem \
  -ca-key=ca-key.pem \
  -config=ca-config.json \
  -profile=kubernetes \
  kube-proxy-csr.json | cfssljson -bare kube-proxy

The Scheduler Client Certificate

cat > kube-scheduler-csr.json <<EOF
{
  "CN": "system:kube-scheduler",
  "key": {
    "algo": "rsa",
    "size": 2048
  },
  "names": [
    {
      "C": "US",
      "L": "Portland",
      "O": "system:kube-scheduler",
      "OU": "Kubernetes The Hard Way",
      "ST": "Oregon"
    }
  ]
}
EOF

cfssl gencert \
  -ca=ca.pem \
  -ca-key=ca-key.pem \
  -config=ca-config.json \
  -profile=kubernetes \
  kube-scheduler-csr.json | cfssljson -bare kube-scheduler

The Kubernetes API Server Certificate

KUBERNETES_PUBLIC_ADDRESS=$(gcloud compute addresses describe kubernetes-the-hard-way \
  --region $(gcloud config get-value compute/region) \
  --format 'value(address)')

KUBERNETES_HOSTNAMES=kubernetes,kubernetes.default,kubernetes.default.svc,kubernetes.default.svc.cluster,kubernetes.svc.cluster.local

cat > kubernetes-csr.json <<EOF
{
  "CN": "kubernetes",
  "key": {
    "algo": "rsa",
    "size": 2048
  },
  "names": [
    {
      "C": "US",
      "L": "Portland",
      "O": "Kubernetes",
      "OU": "Kubernetes The Hard Way",
      "ST": "Oregon"
    }
  ]
}
EOF

cfssl gencert \
  -ca=ca.pem \
  -ca-key=ca-key.pem \
  -config=ca-config.json \
  -hostname=10.32.0.1,10.240.0.10,10.240.0.11,10.240.0.12,${KUBERNETES_PUBLIC_ADDRESS},127.0.0.1,${KUBERNETES_HOSTNAMES} \
  -profile=kubernetes \
  kubernetes-csr.json | cfssljson -bare kubernetes

The Service Account Key Pair

cat > service-account-csr.json <<EOF
{
  "CN": "service-accounts",
  "key": {
    "algo": "rsa",
    "size": 2048
  },
  "names": [
    {
      "C": "US",
      "L": "Portland",
      "O": "Kubernetes",
      "OU": "Kubernetes The Hard Way",
      "ST": "Oregon"
    }
  ]
}
EOF

cfssl gencert \
  -ca=ca.pem \
  -ca-key=ca-key.pem \
  -config=ca-config.json \
  -profile=kubernetes \
  service-account-csr.json | cfssljson -bare service-account

Distribute the Client and Server Certificates

for instance in k8s-worker-0 k8s-worker-1 k8s-worker-2; do
  gcloud compute scp ca.pem ${instance}-key.pem ${instance}.pem ${instance}:~/
done

for instance in k8s-controller-0 k8s-controller-1 k8s-controller-2; do
  gcloud compute scp ca.pem ca-key.pem kubernetes-key.pem kubernetes.pem \
    service-account-key.pem service-account.pem ${instance}:~/
done

5. Kubernetes configuration files

KUBERNETES_PUBLIC_ADDRESS=$(gcloud compute addresses describe kubernetes-the-hard-way \
  --region $(gcloud config get-value compute/region) \
  --format 'value(address)')

The kubelet Kubernetes Configuration File

for instance in k8s-worker-0 k8s-worker-1 k8s-worker-2; do
  kubectl config set-cluster kubernetes-the-hard-way \
    --certificate-authority=ca.pem \
    --embed-certs=true \
    --server=https://${KUBERNETES_PUBLIC_ADDRESS}:6443 \
    --kubeconfig=${instance}.kubeconfig

  kubectl config set-credentials system:node:${instance} \
    --client-certificate=${instance}.pem \
    --client-key=${instance}-key.pem \
    --embed-certs=true \
    --kubeconfig=${instance}.kubeconfig

  kubectl config set-context default \
    --cluster=kubernetes-the-hard-way \
    --user=system:node:${instance} \
    --kubeconfig=${instance}.kubeconfig

  kubectl config use-context default --kubeconfig=${instance}.kubeconfig
done

The kube-proxy Kubernetes Configuration File

kubectl config set-cluster kubernetes-the-hard-way \
  --certificate-authority=ca.pem \
  --embed-certs=true \
  --server=https://${KUBERNETES_PUBLIC_ADDRESS}:6443 \
  --kubeconfig=kube-proxy.kubeconfig

kubectl config set-credentials system:kube-proxy \
  --client-certificate=kube-proxy.pem \
  --client-key=kube-proxy-key.pem \
  --embed-certs=true \
  --kubeconfig=kube-proxy.kubeconfig

kubectl config set-context default \
  --cluster=kubernetes-the-hard-way \
  --user=system:kube-proxy \
  --kubeconfig=kube-proxy.kubeconfig

kubectl config use-context default --kubeconfig=kube-proxy.kubeconfig

The kube-controller-manager Kubernetes Configuration File

kubectl config set-cluster kubernetes-the-hard-way \
  --certificate-authority=ca.pem \
  --embed-certs=true \
  --server=https://127.0.0.1:6443 \
  --kubeconfig=kube-controller-manager.kubeconfig
kubectl config set-credentials system:kube-controller-manager \
  --client-certificate=kube-controller-manager.pem \
  --client-key=kube-controller-manager-key.pem \
  --embed-certs=true \
  --kubeconfig=kube-controller-manager.kubeconfig
kubectl config set-context default \
  --cluster=kubernetes-the-hard-way \
  --user=system:kube-controller-manager \
  --kubeconfig=kube-controller-manager.kubeconfig
kubectl config use-context default --kubeconfig=kube-controller-manager.kubeconfig

The kube-scheduler Kubernetes Configuration File

kubectl config set-cluster kubernetes-the-hard-way \
  --certificate-authority=ca.pem \
  --embed-certs=true \
  --server=https://127.0.0.1:6443 \
  --kubeconfig=kube-scheduler.kubeconfig
kubectl config set-credentials system:kube-scheduler \
  --client-certificate=kube-scheduler.pem \
  --client-key=kube-scheduler-key.pem \
  --embed-certs=true \
  --kubeconfig=kube-scheduler.kubeconfig
kubectl config set-context default \
  --cluster=kubernetes-the-hard-way \
  --user=system:kube-scheduler \
  --kubeconfig=kube-scheduler.kubeconfig
kubectl config use-context default --kubeconfig=kube-scheduler.kubeconfig

The admin Kubernetes Configuration File

kubectl config set-cluster kubernetes-the-hard-way \
  --certificate-authority=ca.pem \
  --embed-certs=true \
  --server=https://127.0.0.1:6443 \
  --kubeconfig=admin.kubeconfig
kubectl config set-credentials admin \
  --client-certificate=admin.pem \
  --client-key=admin-key.pem \
  --embed-certs=true \
  --kubeconfig=admin.kubeconfig
kubectl config set-context default \
  --cluster=kubernetes-the-hard-way \
  --user=admin \
  --kubeconfig=admin.kubeconfig
kubectl config use-context default --kubeconfig=admin.kubeconfig

Distribute the Kubernetes Configuration Files

for instance in k8s-worker-0 k8s-worker-1 k8s-worker-2; do
  gcloud compute scp ${instance}.kubeconfig kube-proxy.kubeconfig ${instance}:~/
done
for instance in k8s-controller-0 k8s-controller-1 k8s-controller-2; do
  gcloud compute scp admin.kubeconfig kube-controller-manager.kubeconfig kube-scheduler.kubeconfig ${instance}:~/
done

6. Generating the Data Encryption Config and Key

ENCRYPTION_KEY=$(head -c 32 /dev/urandom | base64)
cat > encryption-config.yaml <<EOF
kind: EncryptionConfig
apiVersion: v1
resources:
  - resources:
      - secrets
    providers:
      - aescbc:
          keys:
            - name: key1
              secret: ${ENCRYPTION_KEY}
      - identity: {}
EOF
for instance in k8s-controller-0 k8s-controller-1 k8s-controller-2; do
  gcloud compute scp encryption-config.yaml ${instance}:~/
done

7. Bootstrapping the etcd Cluster

wget -q --show-progress --https-only --timestamping "https://github.com/etcd-io/etcd/releases/download/v3.4.15/etcd-v3.4.15-linux-amd64.tar.gz"
tar -xvf etcd-v3.4.15-linux-amd64.tar.gz
sudo mv etcd-v3.4.15-linux-amd64/etcd* /usr/local/bin/
sudo mkdir -p /etc/etcd /var/lib/etcd
sudo chmod 700 /var/lib/etcd
sudo cp ca.pem kubernetes-key.pem kubernetes.pem /etc/etcd/
INTERNAL_IP=$(curl -s -H "Metadata-Flavor: Google" \
  http://metadata.google.internal/computeMetadata/v1/instance/network-interfaces/0/ip)
ETCD_NAME=$(hostname -s)
cat <<EOF | sudo tee /etc/systemd/system/etcd.service
[Unit]
Description=etcd
Documentation=https://github.com/coreos

[Service]
Type=notify
ExecStart=/usr/local/bin/etcd \\
  --name ${ETCD_NAME} \\
  --cert-file=/etc/etcd/kubernetes.pem \\
  --key-file=/etc/etcd/kubernetes-key.pem \\
  --peer-cert-file=/etc/etcd/kubernetes.pem \\
  --peer-key-file=/etc/etcd/kubernetes-key.pem \\
  --trusted-ca-file=/etc/etcd/ca.pem \\
  --peer-trusted-ca-file=/etc/etcd/ca.pem \\
  --peer-client-cert-auth \\
  --client-cert-auth \\
  --initial-advertise-peer-urls https://${INTERNAL_IP}:2380 \\
  --listen-peer-urls https://${INTERNAL_IP}:2380 \\
  --listen-client-urls https://${INTERNAL_IP}:2379,https://127.0.0.1:2379 \\
  --advertise-client-urls https://${INTERNAL_IP}:2379 \\
  --initial-cluster-token etcd-cluster-0 \\
  --initial-cluster k8s-controller-0=https://10.240.0.10:2380,k8s-controller-1=https://10.240.0.11:2380,k8s-controller-2=https://10.240.0.12:2380 \\
  --initial-cluster-state new \\
  --data-dir=/var/lib/etcd
Restart=on-failure
RestartSec=5

[Install]
WantedBy=multi-user.target
EOF
sudo systemctl daemon-reload
sudo systemctl enable etcd
sudo systemctl start etcd

Verification

sudo ETCDCTL_API=3 etcdctl member list \
  --endpoints=https://127.0.0.1:2379 \
  --cacert=/etc/etcd/ca.pem \
  --cert=/etc/etcd/kubernetes.pem \
  --key=/etc/etcd/kubernetes-key.pem

8. Bootstrapping the Kubernetes Control Plane

Run following commands on each node of a control plane. Note that the command Default Region API doesn’t work. As a workaround, I used the command described in this GitHub issue

sudo mkdir -p /etc/kubernetes/config
wget -q --show-progress --https-only --timestamping \
  "https://storage.googleapis.com/kubernetes-release/release/v1.21.0/bin/linux/amd64/kube-apiserver" \
  "https://storage.googleapis.com/kubernetes-release/release/v1.21.0/bin/linux/amd64/kube-controller-manager" \
  "https://storage.googleapis.com/kubernetes-release/release/v1.21.0/bin/linux/amd64/kube-scheduler" \
  "https://storage.googleapis.com/kubernetes-release/release/v1.21.0/bin/linux/amd64/kubectl"
chmod +x kube-apiserver kube-controller-manager kube-scheduler kubectl
sudo mv kube-apiserver kube-controller-manager kube-scheduler kubectl /usr/local/bin/
sudo mkdir -p /var/lib/kubernetes/
sudo mv ca.pem ca-key.pem kubernetes-key.pem kubernetes.pem \
 service-account-key.pem service-account.pem \
  encryption-config.yaml /var/lib/kubernetes/

INTERNAL_IP=$(curl -s -H "Metadata-Flavor: Google" \
  http://metadata.google.internal/computeMetadata/v1/instance/network-interfaces/0/ip)
REGION=$(curl -s -H "Metadata-Flavor: Google" http://metadata.google.internal/computeMetadata/v1/instance/zone | cut -d/ -f 4 | sed 's/.\{2\}$//')
KUBERNETES_PUBLIC_ADDRESS=$(gcloud compute addresses describe kubernetes-the-hard-way \
  --region $REGION \
  --format 'value(address)')


cat <<EOF | sudo tee /etc/systemd/system/kube-apiserver.service
[Unit]
Description=Kubernetes API Server
Documentation=https://github.com/kubernetes/kubernetes

[Service]
ExecStart=/usr/local/bin/kube-apiserver \\
  --advertise-address=${INTERNAL_IP} \\
  --allow-privileged=true \\
  --apiserver-count=3 \\
  --audit-log-maxage=30 \\
  --audit-log-maxbackup=3 \\
  --audit-log-maxsize=100 \\
  --audit-log-path=/var/log/audit.log \\
  --authorization-mode=Node,RBAC \\
  --bind-address=0.0.0.0 \\
  --client-ca-file=/var/lib/kubernetes/ca.pem \\
  --enable-admission-plugins=NamespaceLifecycle,NodeRestriction,LimitRanger,ServiceAccount,DefaultStorageClass,ResourceQuota \\
  --etcd-cafile=/var/lib/kubernetes/ca.pem \\
  --etcd-certfile=/var/lib/kubernetes/kubernetes.pem \\
  --etcd-keyfile=/var/lib/kubernetes/kubernetes-key.pem \\
  --etcd-servers=https://10.240.0.10:2379,https://10.240.0.11:2379,https://10.240.0.12:2379 \\
  --event-ttl=1h \\
  --encryption-provider-config=/var/lib/kubernetes/encryption-config.yaml \\
  --kubelet-certificate-authority=/var/lib/kubernetes/ca.pem \\
  --kubelet-client-certificate=/var/lib/kubernetes/kubernetes.pem \\
  --kubelet-client-key=/var/lib/kubernetes/kubernetes-key.pem \\
  --runtime-config='api/all=true' \\
  --service-account-key-file=/var/lib/kubernetes/service-account.pem \\
  --service-account-signing-key-file=/var/lib/kubernetes/service-account-key.pem \\
  --service-account-issuer=https://${KUBERNETES_PUBLIC_ADDRESS}:6443 \\
  --service-cluster-ip-range=10.32.0.0/24 \\
  --service-node-port-range=30000-32767 \\
  --tls-cert-file=/var/lib/kubernetes/kubernetes.pem \\
  --tls-private-key-file=/var/lib/kubernetes/kubernetes-key.pem \\
  --v=2
Restart=on-failure
RestartSec=5

[Install]
WantedBy=multi-user.target
EOF

sudo mv kube-controller-manager.kubeconfig /var/lib/kubernetes/
cat <<EOF | sudo tee /etc/systemd/system/kube-controller-manager.service
[Unit]
Description=Kubernetes Controller Manager
Documentation=https://github.com/kubernetes/kubernetes

[Service]
ExecStart=/usr/local/bin/kube-controller-manager \\
  --bind-address=0.0.0.0 \\
  --cluster-cidr=10.200.0.0/16 \\
  --cluster-name=kubernetes \\
  --cluster-signing-cert-file=/var/lib/kubernetes/ca.pem \\
  --cluster-signing-key-file=/var/lib/kubernetes/ca-key.pem \\
  --kubeconfig=/var/lib/kubernetes/kube-controller-manager.kubeconfig \\
  --leader-elect=true \\
  --root-ca-file=/var/lib/kubernetes/ca.pem \\
  --service-account-private-key-file=/var/lib/kubernetes/service-account-key.pem \\
  --service-cluster-ip-range=10.32.0.0/24 \\
  --use-service-account-credentials=true \\
  --v=2
Restart=on-failure
RestartSec=5

[Install]
WantedBy=multi-user.target
EOF
sudo mv kube-scheduler.kubeconfig /var/lib/kubernetes/
cat <<EOF | sudo tee /etc/kubernetes/config/kube-scheduler.yaml
apiVersion: kubescheduler.config.k8s.io/v1beta1
kind: KubeSchedulerConfiguration
clientConnection:
  kubeconfig: "/var/lib/kubernetes/kube-scheduler.kubeconfig"
leaderElection:
  leaderElect: true
EOF
cat <<EOF | sudo tee /etc/systemd/system/kube-scheduler.service
[Unit]
Description=Kubernetes Scheduler
Documentation=https://github.com/kubernetes/kubernetes

[Service]
ExecStart=/usr/local/bin/kube-scheduler \\
  --config=/etc/kubernetes/config/kube-scheduler.yaml \\
  --v=2
Restart=on-failure
RestartSec=5

[Install]
WantedBy=multi-user.target
EOF

sudo systemctl daemon-reload
sudo systemctl enable kube-apiserver kube-controller-manager kube-scheduler
sudo systemctl start kube-apiserver kube-controller-manager kube-scheduler

Enable HTTP Check

sudo apt-get update
sudo apt-get install -y nginx

cat > kubernetes.default.svc.cluster.local <<EOF
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;
  }
}
EOF
sudo mv kubernetes.default.svc.cluster.local /etc/nginx/sites-available/kubernetes.default.svc.cluster.local
sudo ln -s /etc/nginx/sites-available/kubernetes.default.svc.cluster.local /etc/nginx/sites-enabled/
sudo systemctl restart nginx
sudo systemctl enable nginx

Verification

kubectl cluster-info --kubeconfig admin.kubeconfig
curl -H "Host: kubernetes.default.svc.cluster.local" -i http://127.0.0.1/healthz

Kubernetes Cluster configuration

RBAC

cat <<EOF | kubectl apply --kubeconfig admin.kubeconfig -f -
apiVersion: rbac.authorization.k8s.io/v1
kind: ClusterRole
metadata:
  annotations:
    rbac.authorization.kubernetes.io/autoupdate: "true"
  labels:
    kubernetes.io/bootstrapping: rbac-defaults
  name: system:kube-apiserver-to-kubelet
rules:
  - apiGroups:
      - ""
    resources:
      - nodes/proxy
      - nodes/stats
      - nodes/log
      - nodes/spec
      - nodes/metrics
    verbs:
      - "*"
EOF
cat <<EOF | kubectl apply --kubeconfig admin.kubeconfig -f -
apiVersion: rbac.authorization.k8s.io/v1
kind: ClusterRoleBinding
metadata:
  name: system:kube-apiserver
  namespace: ""
roleRef:
  apiGroup: rbac.authorization.k8s.io
  kind: ClusterRole
  name: system:kube-apiserver-to-kubelet
subjects:
  - apiGroup: rbac.authorization.k8s.io
    kind: User
    name: kubernetes
EOF

Front Load Balancer

KUBERNETES_PUBLIC_ADDRESS=$(gcloud compute addresses describe kubernetes-the-hard-way \
  --region $(gcloud config get-value compute/region) \
  --format 'value(address)')
gcloud compute http-health-checks create kubernetes \
  --description "Kubernetes Health Check" \
  --host "kubernetes.default.svc.cluster.local" \
  --request-path "/healthz"
gcloud compute firewall-rules create kubernetes-the-hard-way-allow-health-check \
  --network kubernetes-the-hard-way \
  --source-ranges 209.85.152.0/22,209.85.204.0/22,35.191.0.0/16 \
  --allow tcp
gcloud compute target-pools create kubernetes-target-pool \
  --http-health-check kubernetes
gcloud compute target-pools add-instances kubernetes-target-pool \
 --instances k8s-controller-0,k8s-controller-1,k8s-controller-2
gcloud compute forwarding-rules create kubernetes-forwarding-rule \
  --address ${KUBERNETES_PUBLIC_ADDRESS} \
  --ports 6443 \
  --region $(gcloud config get-value compute/region) \
  --target-pool kubernetes-target-pool

Verification

KUBERNETES_PUBLIC_ADDRESS=$(gcloud compute addresses describe kubernetes-the-hard-way \
  --region $(gcloud config get-value compute/region) \
  --format 'value(address)')
curl --cacert ca.pem https://${KUBERNETES_PUBLIC_ADDRESS}:6443/version

9. Bootstrapping the Kubernetes Worker Nodes

Provision a worker node

sudo apt-get update
sudo apt-get -y install socat conntrack ipset
wget -q --show-progress --https-only --timestamping \
  https://github.com/kubernetes-sigs/cri-tools/releases/download/v1.21.0/crictl-v1.21.0-linux-amd64.tar.gz \
  https://github.com/opencontainers/runc/releases/download/v1.0.0-rc93/runc.amd64 \
  https://github.com/containernetworking/plugins/releases/download/v0.9.1/cni-plugins-linux-amd64-v0.9.1.tgz \
  https://github.com/containerd/containerd/releases/download/v1.4.4/containerd-1.4.4-linux-amd64.tar.gz \
  https://storage.googleapis.com/kubernetes-release/release/v1.21.0/bin/linux/amd64/kubectl \
  https://storage.googleapis.com/kubernetes-release/release/v1.21.0/bin/linux/amd64/kube-proxy \
  https://storage.googleapis.com/kubernetes-release/release/v1.21.0/bin/linux/amd64/kubelet
sudo mkdir -p \
  /etc/cni/net.d \
  /opt/cni/bin \
  /var/lib/kubelet \
  /var/lib/kube-proxy \
  /var/lib/kubernetes \
  /var/run/kubernetes
mkdir containerd
tar -xvf crictl-v1.21.0-linux-amd64.tar.gz
tar -xvf containerd-1.4.4-linux-amd64.tar.gz -C containerd
sudo tar -xvf cni-plugins-linux-amd64-v0.9.1.tgz -C /opt/cni/bin/
sudo mv runc.amd64 runc
chmod +x crictl kubectl kube-proxy kubelet runc
sudo mv crictl kubectl kube-proxy kubelet runc /usr/local/bin/
sudo mv containerd/bin/* /bin/

Configure CNI Networking

IPAM: IP Address Allocation
ipMasq: Set up IP masquarade. This is necessary if the host will act as a gateway to subnets that are not able to route to the IP assigned to the container

POD_CIDR=$(curl -s -H "Metadata-Flavor: Google" \
  http://metadata.google.internal/computeMetadata/v1/instance/attributes/pod-cidr)
cat <<EOF | sudo tee /etc/cni/net.d/10-bridge.conf
{
    "cniVersion": "0.4.0",
    "name": "bridge",
    "type": "bridge",
    "bridge": "cnio0",
    "isGateway": true,
    "ipMasq": true,
    "ipam": {
        "type": "host-local",
        "ranges": [
          [{"subnet": "${POD_CIDR}"}]
        ],
        "routes": [{"dst": "0.0.0.0/0"}]
    }
}
EOF
cat <<EOF | sudo tee /etc/cni/net.d/99-loopback.conf
{
    "cniVersion": "0.4.0",
    "name": "lo",
    "type": "loopback"
}
EOF

Containerd

sudo mkdir -p /etc/containerd/
cat << EOF | sudo tee /etc/containerd/config.toml
[plugins]
  [plugins.cri.containerd]
    snapshotter = "overlayfs"
    [plugins.cri.containerd.default_runtime]
      runtime_type = "io.containerd.runtime.v1.linux"
      runtime_engine = "/usr/local/bin/runc"
      runtime_root = ""
EOF
cat <<EOF | sudo tee /etc/systemd/system/containerd.service
[Unit]
Description=containerd container runtime
Documentation=https://containerd.io
After=network.target

[Service]
ExecStartPre=/sbin/modprobe overlay
ExecStart=/bin/containerd
Restart=always
RestartSec=5
Delegate=yes
KillMode=process
OOMScoreAdjust=-999
LimitNOFILE=1048576
LimitNPROC=infinity
LimitCORE=infinity

[Install]
WantedBy=multi-user.target
EOF

Configure Kubelet

sudo mv ${HOSTNAME}-key.pem ${HOSTNAME}.pem /var/lib/kubelet/
sudo mv ${HOSTNAME}.kubeconfig /var/lib/kubelet/kubeconfig
sudo mv ca.pem /var/lib/kubernetes/
cat <<EOF | sudo tee /var/lib/kubelet/kubelet-config.yaml
kind: KubeletConfiguration
apiVersion: kubelet.config.k8s.io/v1beta1
authentication:
  anonymous:
    enabled: false
  webhook:
    enabled: true
  x509:
    clientCAFile: "/var/lib/kubernetes/ca.pem"
authorization:
  mode: Webhook
clusterDomain: "cluster.local"
clusterDNS:
  - "10.32.0.10"
podCIDR: "${POD_CIDR}"
resolvConf: "/run/systemd/resolve/resolv.conf"
runtimeRequestTimeout: "15m"
tlsCertFile: "/var/lib/kubelet/${HOSTNAME}.pem"
tlsPrivateKeyFile: "/var/lib/kubelet/${HOSTNAME}-key.pem"
EOF

  cat <<EOF | sudo tee /etc/systemd/system/kubelet.service
[Unit]
Description=Kubernetes Kubelet
Documentation=https://github.com/kubernetes/kubernetes
After=containerd.service
Requires=containerd.service

[Service]
ExecStart=/usr/local/bin/kubelet \\
  --config=/var/lib/kubelet/kubelet-config.yaml \\
  --container-runtime=remote \\
  --container-runtime-endpoint=unix:///var/run/containerd/containerd.sock \\
  --image-pull-progress-deadline=2m \\
  --kubeconfig=/var/lib/kubelet/kubeconfig \\
  --network-plugin=cni \\
  --register-node=true \\
  --v=2
Restart=on-failure
RestartSec=5

[Install]
WantedBy=multi-user.target
EOF

Configure the Kube Proxy

sudo mv kube-proxy.kubeconfig /var/lib/kube-proxy/kubeconfig
cat <<EOF | sudo tee /var/lib/kube-proxy/kube-proxy-config.yaml
kind: KubeProxyConfiguration
apiVersion: kubeproxy.config.k8s.io/v1alpha1
clientConnection:
  kubeconfig: "/var/lib/kube-proxy/kubeconfig"
mode: "iptables"
clusterCIDR: "10.200.0.0/16"
EOF
cat <<EOF | sudo tee /etc/systemd/system/kube-proxy.service
[Unit]
Description=Kubernetes Kube Proxy
Documentation=https://github.com/kubernetes/kubernetes

[Service]
ExecStart=/usr/local/bin/kube-proxy \\
  --config=/var/lib/kube-proxy/kube-proxy-config.yaml
Restart=on-failure
RestartSec=5

[Install]
WantedBy=multi-user.target
EOF

Start daemons

sudo systemctl daemon-reload
sudo systemctl enable containerd kubelet kube-proxy
sudo systemctl start containerd kubelet kube-proxy

Confirmation

$ kubectl get nodes --kubeconfig admin.kubeconfig

10. Configuring kubectl for Remote Access

kubectl

KUBERNETES_PUBLIC_ADDRESS=$(gcloud compute addresses describe kubernetes-the-hard-way \
  --region $(gcloud config get-value compute/region) \
  --format 'value(address)')
kubectl config set-cluster kubernetes-the-hard-way \
  --certificate-authority=ca.pem \
  --embed-certs=true \
  --server=https://${KUBERNETES_PUBLIC_ADDRESS}:6443
kubectl config set-credentials admin \
  --client-certificate=admin.pem \
  --client-key=admin-key.pem
kubectl config set-context kubernetes-the-hard-way \
  --cluster=kubernetes-the-hard-way \
  --user=admin
kubectl config use-context kubernetes-the-hard-way

11. Provisioning Pod Network Routes

for instance in k8s-worker-0 k8s-worker-1 k8s-worker-2; do
  gcloud compute instances describe ${instance} \
    --format 'value[separator=" "](networkInterfaces[0].networkIP,metadata.items[0].value)'
done

for i in 0 1 2; do
  gcloud compute routes create kubernetes-route-10-200-${i}-0-24 \
    --network kubernetes-the-hard-way \
    --next-hop-address 10.240.0.2${i} \
    --destination-range 10.200.${i}.0/24
done

Confirmation.

gcloud compute routes list --filter "network: kubernetes-the-hard-way"

12. Deploying the DNS Cluster Add-on

There is no core dns 1.8 file anymore. So, following this GitHub comment, I downloaded CoreDNS 1.7 committed in the repository originally.

kubectl apply -f https://raw.githubusercontent.com/kelseyhightower/kubernetes-the-hard-way/master/deployments/coredns-1.7.0.yaml

Confirm application

bash-5.2$ kubectl get pods -l k8s-app=kube-dns -n kube-system
NAME                       READY   STATUS    RESTARTS   AGE
coredns-748f75f5fb-wqqcb   1/1     Running   0          13s
coredns-748f75f5fb-wqr9m   1/1     Running   0          13s

Verification

kubectl get pods -l run=busybox
POD_NAME=$(kubectl get pods -l run=busybox -o jsonpath="{.items[0].metadata.name}")
kubectl exec -ti $POD_NAME -- nslookup kubernetes

Output was

Server:    10.32.0.10
Address 1: 10.32.0.10 kube-dns.kube-system.svc.cluster.local

Name:      kubernetes
Address 1: 10.32.0.1 kubernetes.default.svc.cluster.local

These IPs came from services

bash-5.2$ kubectl get svc -n kube-system -o wide
NAME       TYPE        CLUSTER-IP   EXTERNAL-IP   PORT(S)                  AGE     SELECTOR
kube-dns   ClusterIP   10.32.0.10   <none>        53/UDP,53/TCP,9153/TCP   9m32s   k8s-app=kube-dns

bash-5.2$ kubectl get svc -owide
NAME         TYPE        CLUSTER-IP   EXTERNAL-IP   PORT(S)   AGE   SELECTOR
kubernetes   ClusterIP   10.32.0.1    <none>        443/TCP   14d   <none>

bash-5.2$ kubectl get svc -o yaml kubernetes
apiVersion: v1
kind: Service
metadata:
  creationTimestamp: "2023-07-16T04:03:32Z"
  labels:
    component: apiserver
    provider: kubernetes
  name: kubernetes
  namespace: default
  resourceVersion: "208"
  uid: a0b09bfc-5464-4ddc-ab21-3787ac9dec44
spec:
  clusterIP: 10.32.0.1
  clusterIPs:
  - 10.32.0.1
  ipFamilies:
  - IPv4
  ipFamilyPolicy: SingleStack
  ports:
  - name: https
    port: 443
    protocol: TCP
    targetPort: 6443
  sessionAffinity: None
  type: ClusterIP
status:
  loadBalancer: {}

I couldn’t find where this service is defined. Maybe kube-proxy or kubelet configurations included it.

13. Smoke Test

Secret

kubectl create secret generic kubernetes-the-hard-way \
  --from-literal="mykey=mydata"
gcloud compute ssh k8s-controller-0 \
  --command "sudo ETCDCTL_API=3 etcdctl get \
  --endpoints=https://127.0.0.1:2379 \
  --cacert=/etc/etcd/ca.pem \
  --cert=/etc/etcd/kubernetes.pem \
  --key=/etc/etcd/kubernetes-key.pem\
  /registry/secrets/default/kubernetes-the-hard-way | hexdump -C"

etcd

Just looking around etcd data.

Checking keys stored in etcd following this comment

$ sudo ETCDCTL_API=3 etcdctl --endpoints=https://127.0.0.1:2379 --cacert=/etc/etcd/ca.pem --cert=/etc/etcd/kubernetes.pem --key=/etc/etcd/kubernetes-key.pem get / --prefix --keys-only | head -n 5
/registry/apiregistration.k8s.io/apiservices/v1.
/registry/apiregistration.k8s.io/apiservices/v1.admissionregistration.k8s.io
/registry/apiregistration.k8s.io/apiservices/v1.apiextensions.k8s.io

Get a revision of a key

$ sudo ETCDCTL_API=3 etcdctl --endpoints=https://127.0.0.1:2379 --cacert=/etc/etcd/ca.pem --cert=/etc/etcd/kubernetes.pem --key=/etc/etcd/kubernetes-key.pem get /registry/deployments/kube-system/coredns  -w json | jq .
{
  "header": {
    "cluster_id": 4502693191618639400,
    "member_id": 17982242243123227000,
    "revision": 2046681,
    "raft_term": 123
  },
  "kvs": [
    {
      "key": "L3JlZ2lzdHJ5L2RlcGxveW1lbnRzL2t1YmUtc3lzdGVtL2NvcmVkbnM=",
      "create_revision": 2041628,
      "mod_revision": 2041695,
      "version": 6,
      "value": "<BASE 64 ENCODED>"
    }
  ],
  "count": 1
}

Deployment

kubectl create deployment nginx --image=nginx
POD_NAME=$(kubectl get pods -l app=nginx -o jsonpath="{.items[0].metadata.name}")

Port forwarding

$ kubectl port-forward $POD_NAME 8080:80
$ curl --head http://127.0.0.1:8080
HTTP/1.1 200 OK
Server: nginx/1.25.1
Date: Sun, 30 Jul 2023 23:38:57 GMT
Content-Type: text/html
Content-Length: 615
Last-Modified: Tue, 13 Jun 2023 15:08:10 GMT
Connection: keep-alive
ETag: "6488865a-267"
Accept-Ranges: bytes

Logs

$ kubectl logs $POD_NAME
/docker-entrypoint.sh: /docker-entrypoint.d/ is not empty, will attempt to perform configuration
/docker-entrypoint.sh: Looking for shell scripts in /docker-entrypoint.d/
/docker-entrypoint.sh: Launching /docker-entrypoint.d/10-listen-on-ipv6-by-default.sh
10-listen-on-ipv6-by-default.sh: info: Getting the checksum of /etc/nginx/conf.d/default.conf
10-listen-on-ipv6-by-default.sh: info: Enabled listen on IPv6 in /etc/nginx/conf.d/default.conf
/docker-entrypoint.sh: Sourcing /docker-entrypoint.d/15-local-resolvers.envsh
/docker-entrypoint.sh: Launching /docker-entrypoint.d/20-envsubst-on-templates.sh
/docker-entrypoint.sh: Launching /docker-entrypoint.d/30-tune-worker-processes.sh
/docker-entrypoint.sh: Configuration complete; ready for start up
2023/07/30 23:36:31 [notice] 1#1: using the "epoll" event method
2023/07/30 23:36:31 [notice] 1#1: nginx/1.25.1
2023/07/30 23:36:31 [notice] 1#1: built by gcc 12.2.0 (Debian 12.2.0-14)
2023/07/30 23:36:31 [notice] 1#1: OS: Linux 5.15.0-1036-gcp
2023/07/30 23:36:31 [notice] 1#1: getrlimit(RLIMIT_NOFILE): 1048576:1048576
2023/07/30 23:36:31 [notice] 1#1: start worker processes
2023/07/30 23:36:31 [notice] 1#1: start worker process 28
2023/07/30 23:36:31 [notice] 1#1: start worker process 29
127.0.0.1 - - [30/Jul/2023:23:38:47 +0000] "GET / HTTP/1.1" 200 615 "-" "curl/7.88.1" "-"
127.0.0.1 - - [30/Jul/2023:23:38:50 +0000] "GET / HTTP/1.1" 200 615 "-" "curl/7.88.1" "-"
127.0.0.1 - - [30/Jul/2023:23:38:57 +0000] "HEAD / HTTP/1.1" 200 0 "-" "curl/7.88.1" "-"

Exec

$ kubectl exec -ti $POD_NAME -- nginx -v
nginx version: nginx/1.25.1

Services

kubectl expose deployment nginx --port 80 --type NodePort
NODE_PORT=$(kubectl get svc nginx \
  --output=jsonpath='{range .spec.ports[0]}{.nodePort}')
gcloud compute firewall-rules create kubernetes-the-hard-way-allow-nginx-service \
  --allow=tcp:${NODE_PORT} \
  --network kubernetes-the-hard-way

Confirmation

EXTERNAL_IP=$(gcloud compute instances describe k8s-worker-0 \
  --format 'value(networkInterfaces[0].accessConfigs[0].natIP)')
curl -I http://${EXTERNAL_IP}:${NODE_PORT}

14. Cleaning Up

Following steps haven’t been tested yet.

gcloud -q compute instances delete \
  k8s-controller-0 k8s-controller-1 k8s-controller-2 \
  k8s-worker-0 k8s-worker-1 k8s-worker-2 \
  --zone $(gcloud config get-value compute/zone)

gcloud -q compute forwarding-rules delete kubernetes-forwarding-rule \
  --region $(gcloud config get-value compute/region)
gcloud -q compute target-pools delete kubernetes-target-pool
gcloud -q compute http-health-checks delete kubernetes
gcloud -q compute addresses delete kubernetes-the-hard-way

gcloud -q compute firewall-rules delete \
  kubernetes-the-hard-way-allow-nginx-service \
  kubernetes-the-hard-way-allow-internal \
  kubernetes-the-hard-way-allow-external \
  kubernetes-the-hard-way-allow-health-check

gcloud -q compute routes delete \
  kubernetes-route-10-200-0-0-24 \
  kubernetes-route-10-200-1-0-24 \
  kubernetes-route-10-200-2-0-24
gcloud -q compute networks subnets delete kubernetes
gcloud -q compute networks delete kubernetes-the-hard-way

gcloud -q compute addresses delete kubernetes-the-hard-way \
  --region $(gcloud config get-value compute/region)

Last updated on January 25, 2025

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