Introduce CI/CD

.gitea/workflows/deploy.yml

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+name: Validate and deploy CoreDNS scheduling
+on: [push, pull_request]
+env:
+  KUBECTL_VERSION: v1.36.3
+  KUBERNETES_API: https://host.containers.internal:6443
+  KUBERNETES_TLS_SERVER_NAME: 192.168.0.2
+jobs:
+  validate:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - run: bash test.sh
+  deploy:
+    if: gitea.ref == 'refs/heads/main'
+    needs: validate
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - name: Install kubectl
+        run: |
+          curl -fsSL -o "${RUNNER_TEMP}/kubectl" "https://dl.k8s.io/release/${KUBECTL_VERSION}/bin/linux/amd64/kubectl"
+          curl -fsSL -o "${RUNNER_TEMP}/kubectl.sha256" "https://dl.k8s.io/release/${KUBECTL_VERSION}/bin/linux/amd64/kubectl.sha256"
+          printf '%s  %s\n' "$(cat "${RUNNER_TEMP}/kubectl.sha256")" "${RUNNER_TEMP}/kubectl" | sha256sum -c
+          chmod 0700 "${RUNNER_TEMP}/kubectl"
+      - name: Configure Kubernetes access
+        env:
+          KUBE_CONFIG_BASE64: ${{ secrets.KUBE_CONFIG_BASE64 }}
+        run: |
+          test -n "${KUBE_CONFIG_BASE64}"
+          printf '%s' "${KUBE_CONFIG_BASE64}" | base64 -d > "${RUNNER_TEMP}/kubeconfig"
+          chmod 0600 "${RUNNER_TEMP}/kubeconfig"
+          export KUBECONFIG="${RUNNER_TEMP}/kubeconfig"
+          "${RUNNER_TEMP}/kubectl" config set-cluster cluster --server="${KUBERNETES_API}" --tls-server-name="${KUBERNETES_TLS_SERVER_NAME}"
+      - name: Apply and verify
+        run: |
+          export KUBECONFIG="${RUNNER_TEMP}/kubeconfig"
+          "${RUNNER_TEMP}/kubectl" -n kube-system patch deployment coredns --type=strategic --patch-file coredns-scheduling-patch.yaml --dry-run=server
+          "${RUNNER_TEMP}/kubectl" apply --server-side --force-conflicts --dry-run=server -f coredns-pdb.yaml
+          "${RUNNER_TEMP}/kubectl" -n kube-system patch deployment coredns --type=strategic --patch-file coredns-scheduling-patch.yaml
+          "${RUNNER_TEMP}/kubectl" apply --server-side --force-conflicts -f coredns-pdb.yaml
+          for attempt in {1..60}; do
+            state=$("${RUNNER_TEMP}/kubectl" -n kube-system get deployment coredns -o jsonpath='{.metadata.generation}|{.status.observedGeneration}|{.spec.replicas}|{.status.updatedReplicas}|{.status.readyReplicas}|{.status.availableReplicas}')
+            IFS='|' read -r generation observed desired updated ready available <<< "$state"
+            [[ "$generation" == "$observed" && "$desired" == "$updated" && "$desired" == "$ready" && "$desired" == "$available" ]] && exit 0
+            sleep 5
+          done
+          exit 1

.gitignore

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+*.kubeconfig
+*.secret
+*secrets*.env

README.md

@@ -1,2 +1,26 @@
-# coredns-deployment
+# CoreDNS scheduling
 
+CoreDNS runs with two replicas on distinct ODROID H3 worker nodes. The required
+node affinity prevents it from being scheduled on the experimental control-plane
+node (`arschrock`), while required pod anti-affinity prevents both replicas from
+sharing a worker.
+
+Apply and verify the configuration with:
+
+```sh
+kubectl -n kube-system patch deployment coredns \
+  --type=strategic \
+  --patch-file coredns-scheduling-patch.yaml
+kubectl apply -f coredns-pdb.yaml
+kubectl -n kube-system rollout status deployment/coredns
+kubectl -n kube-system get pods -l k8s-app=kube-dns -o wide
+```
+
+The ODROID worker nodes must retain the label `odroid-h3=enabled`.
+
+`./install.sh` performs those steps for an administrator. Gitea Actions checks
+the manifests on every branch and updates only the exact existing
+`kube-system/coredns` Deployment and PodDisruptionBudget on `main`. Its identity
+cannot read Secrets, create or delete resources, or change any other workload.
+Run `./create-ci-kubeconfig.sh` once and store only its final line as the
+repository Actions secret `KUBE_CONFIG_BASE64`.

ci-deployer.yaml

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+apiVersion: v1
+kind: ServiceAccount
+metadata:
+  name: coredns-config-deployer
+  namespace: kube-system
+automountServiceAccountToken: false
+---
+apiVersion: rbac.authorization.k8s.io/v1
+kind: Role
+metadata:
+  name: coredns-config-deployer
+  namespace: kube-system
+rules:
+  - apiGroups: [apps]
+    resources: [deployments]
+    resourceNames: [coredns]
+    verbs: [get, patch, update]
+  - apiGroups: [policy]
+    resources: [poddisruptionbudgets]
+    resourceNames: [coredns]
+    verbs: [get, patch, update]
+---
+apiVersion: rbac.authorization.k8s.io/v1
+kind: RoleBinding
+metadata:
+  name: coredns-config-deployer
+  namespace: kube-system
+roleRef:
+  apiGroup: rbac.authorization.k8s.io
+  kind: Role
+  name: coredns-config-deployer
+subjects:
+  - kind: ServiceAccount
+    name: coredns-config-deployer
+    namespace: kube-system
+---
+apiVersion: v1
+kind: Secret
+metadata:
+  name: coredns-config-deployer-token
+  namespace: kube-system
+  annotations:
+    kubernetes.io/service-account.name: coredns-config-deployer
+type: kubernetes.io/service-account-token

coredns-pdb.yaml

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+apiVersion: policy/v1
+kind: PodDisruptionBudget
+metadata:
+  name: coredns
+  namespace: kube-system
+spec:
+  minAvailable: 1
+  selector:
+    matchLabels:
+      k8s-app: kube-dns

coredns-scheduling-patch.yaml

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+apiVersion: apps/v1
+kind: Deployment
+metadata:
+  name: coredns
+  namespace: kube-system
+spec:
+  replicas: 2
+  template:
+    spec:
+      affinity:
+        nodeAffinity:
+          requiredDuringSchedulingIgnoredDuringExecution:
+            nodeSelectorTerms:
+              - matchExpressions:
+                  - key: odroid-h3
+                    operator: In
+                    values:
+                      - enabled
+        podAntiAffinity:
+          requiredDuringSchedulingIgnoredDuringExecution:
+            - labelSelector:
+                matchLabels:
+                  k8s-app: kube-dns
+              topologyKey: kubernetes.io/hostname

create-ci-kubeconfig.sh

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+#!/usr/bin/env bash
+set -euo pipefail
+project_dir=$(cd -- "$(dirname -- "${BASH_SOURCE[0]}")" && pwd)
+namespace=kube-system
+service_account=coredns-config-deployer
+secret=coredns-config-deployer-token
+ssh_host=${KUBECTL_SSH_HOST:-}
+ssh_config=${SSH_CONFIG:-}
+cluster_kubectl() { if [[ -n "$ssh_host" ]]; then if [[ -n "$ssh_config" ]]; then ssh -F "$ssh_config" "$ssh_host" kubectl "$@"; else ssh "$ssh_host" kubectl "$@"; fi; else kubectl "$@"; fi; }
+if [[ -n "$ssh_host" ]]; then cluster_kubectl apply -f - < "$project_dir/ci-deployer.yaml" >&2; else cluster_kubectl apply -f "$project_dir/ci-deployer.yaml" >&2; fi
+for attempt in {1..30}; do
+  if cluster_kubectl -n "$namespace" get secret "$secret" -o jsonpath='{.data.token}' 2>/dev/null | grep -q .; then break; fi
+  [[ "$attempt" != 30 ]] || { echo 'Timed out waiting for service-account token' >&2; exit 1; }
+  sleep 1
+done
+work=$(mktemp -d); trap 'rm -rf "$work"' EXIT
+server=$(cluster_kubectl config view --minify -o jsonpath='{.clusters[0].cluster.server}')
+cluster_kubectl -n "$namespace" get secret "$secret" -o jsonpath='{.data.ca\.crt}' | base64 -d > "$work/ca.crt"
+token=$(cluster_kubectl -n "$namespace" get secret "$secret" -o jsonpath='{.data.token}' | base64 -d)
+export KUBECONFIG="$work/config"
+kubectl config set-cluster cluster --server="$server" --certificate-authority="$work/ca.crt" --embed-certs=true >/dev/null
+kubectl config set-credentials "$service_account" --token="$token" >/dev/null
+kubectl config set-context coredns --cluster=cluster --user="$service_account" --namespace="$namespace" >/dev/null
+kubectl config use-context coredns >/dev/null
+echo 'Store this line as Gitea Actions secret KUBE_CONFIG_BASE64; do not commit it.' >&2
+base64 -w0 "$KUBECONFIG"; printf '\n'

install.sh

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+#!/bin/sh
+set -eu
+project_dir=$(CDPATH= cd -- "$(dirname -- "$0")" && pwd)
+kubectl -n kube-system patch deployment coredns --type=strategic \
+  --patch-file "$project_dir/coredns-scheduling-patch.yaml"
+kubectl apply -f "$project_dir/coredns-pdb.yaml"
+kubectl -n kube-system rollout status deployment/coredns --timeout=5m

test.sh

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+#!/usr/bin/env bash
+set -euo pipefail
+dir=$(cd -- "$(dirname -- "${BASH_SOURCE[0]}")" && pwd)
+sh -n "$dir/install.sh"
+bash -n "$dir/create-ci-kubeconfig.sh" "$dir/test.sh"
+grep -Fq 'namespace: kube-system' "$dir/coredns-scheduling-patch.yaml"
+grep -Fq 'odroid-h3' "$dir/coredns-scheduling-patch.yaml"
+grep -Fq 'requiredDuringSchedulingIgnoredDuringExecution' "$dir/coredns-scheduling-patch.yaml"
+image=ghcr.io/yannh/kubeconform:v0.7.0@sha256:85dbef6b4b312b99133decc9c6fc9495e9fc5f92293d4ff3b7e1b30f5611823c
+docker run --rm -i "$image" -strict -exit-on-error -summary < "$dir/coredns-pdb.yaml"
+docker run --rm -i "$image" -strict -exit-on-error -summary < "$dir/ci-deployer.yaml"
+echo 'CoreDNS scheduling manifests and least-privilege CI resources are valid.'