Move kea entrypoints out of Go fmt.Sprintf into an initContainer

Container entrypoints were rendered as `fmt.Sprintf` shell strings in Go, so
every entrypoint fix needed a full operator release, nothing was shellcheckable,
and the escaping was a hazard.

How:
- Add a `kea-init` initContainer that finalises the per-pod config and
  bounded-waits for HA peer DNS, replacing the in-entrypoint retry. It hardens
  the shared run dir to 0750, substitutes `this-server-name` from the pod
  ordinal (`POD_NAME` via the downward API), stages both configs into the shared
  emptyDir, and gates on `kea-dhcp4 -t` (60x2s) — failing loud after the cap so
  the kubelet restarts it instead of starting a doomed server.
- Run the main kea-dhcp4 / kea-ctrl-agent containers with kea exec'd directly,
  dropping both wrapper shells.
- Replace the two `fmt.Sprintf` entrypoints with a single committed
  `internal/kea/scripts/init.sh` embedded via `go:embed` and parameterised
  entirely by env vars — no Go string interpolation.
- Add a shellcheck step to the pre-commit pipeline.

Test:
- Assert the pod shape: one kea-init initContainer, POD_NAME from the downward
  API, main containers exec kea directly, and the ConfigMap carries init.sh (not
  the old per-container entrypoints).
- Assert init.sh hardens the socket dir, gates on `kea-dhcp4 -t`, fails loud
  after the cap, and is free of fmt verbs.
- shellcheck the embedded script.

.woodpecker/pre-commit.yaml

@@ -17,3 +17,18 @@ steps:
     commands:
       - test -z "$(gofmt -l .)"
       - go vet ./...
+
+  - name: shellcheck
+    image: koalaman/shellcheck-alpine:stable
+    backend_options:
+      kubernetes:
+        serviceAccountName: kea-operator-ci
+        resources:
+          requests:
+            memory: 256Mi
+            cpu: "500m"
+          limits:
+            memory: 512Mi
+            cpu: "1"
+    commands:
+      - shellcheck --shell=sh internal/kea/scripts/*.sh

README.md

@@ -35,9 +35,18 @@ Kea HA needs a **stable per-peer identity** (each server must know which peer it
 is, and peers reference each other by stable URL). That is exactly why this
 operator (like bind-operator) uses a **StatefulSet** rather than a bare
 Deployment: pods get stable ordinals (`<cluster>-0`, `<cluster>-1`) and headless
-DNS, the entrypoint derives `this-server-name` from the ordinal, and the peer
+DNS, an initContainer derives `this-server-name` from the ordinal, and the peer
 URLs are DNS names (never pod IPs, so the config hash never loops).
 
+Startup preconditions live in a `kea-init` initContainer (a committed,
+shellcheck-clean `internal/kea/scripts/init.sh` embedded via `go:embed` and
+parameterised by env vars — no shell is interpolated in Go). It hardens the
+shared run dir to `0750`, substitutes `this-server-name` from the pod ordinal,
+stages both configs into the shared `emptyDir`, and bounded-waits for the HA
+peer DNS to resolve (`kea-dhcp4 -t`, failing loud after the cap so the kubelet
+restarts it). The main `kea-dhcp4` and `kea-ctrl-agent` containers then exec kea
+directly with no wrapper shell.
+
 ### Anycast routing caveat (deployment follow-up)
 
 The DHCP `Service` is a `LoadBalancer` intended to receive a PureLB anycast IP;

internal/controller/keacluster_controller.go

@@ -3,6 +3,7 @@ package controller
 import (
 	"context"
 	"fmt"
+	"strconv"
 
 	appsv1 "k8s.io/api/apps/v1"
 	corev1 "k8s.io/api/core/v1"
@@ -173,10 +174,9 @@ func (r *KeaClusterReconciler) reconcileConfigMap(ctx context.Context, c *v1alph
 	_, err = ctrl.CreateOrUpdate(ctx, r.Client, cm, func() error {
 		cm.Labels = commonLabels(c.Name)
 		cm.Data = map[string]string{
-			"kea-dhcp4.conf":          dhcp4,
-			"kea-ctrl-agent.conf":     agent,
-			"entrypoint-dhcp4.sh":     kea.EntrypointDHCP4(),
-			"entrypoint-ctrlagent.sh": kea.EntrypointCtrlAgent(),
+			"kea-dhcp4.conf":      dhcp4,
+			"kea-ctrl-agent.conf": agent,
+			"init.sh":             kea.InitScript(),
 		}
 		return ctrl.SetControllerReference(c, cm, r.Scheme)
 	})
@@ -288,10 +288,21 @@ func (r *KeaClusterReconciler) podTemplate(c *v1alpha1.KeaCluster, image, hash s
 		{Name: "run", MountPath: kea.RunDir},
 	}
 
+	// The initContainer finalises the per-pod config and bounded-waits for HA
+	// peer DNS; the main containers then exec kea directly with no wrapper shell.
+	initC := corev1.Container{
+		Name:         kea.ContainerInit,
+		Image:        image,
+		Command:      []string{"/bin/sh", kea.InitScriptPath},
+		Env:          initEnv(),
+		Resources:    c.Spec.Resources,
+		VolumeMounts: mounts,
+	}
+
 	dhcp4 := corev1.Container{
 		Name:      kea.ContainerDHCP4,
 		Image:     image,
-		Command:   []string{"/bin/sh", kea.ConfigDir + "/entrypoint-dhcp4.sh"},
+		Command:   []string{kea.DHCP4Bin, "-c", kea.DHCP4ConfPath},
 		Resources: c.Spec.Resources,
 		Ports: []corev1.ContainerPort{
 			{Name: "dhcp", ContainerPort: kea.DHCP4Port, Protocol: corev1.ProtocolUDP},
@@ -301,7 +312,7 @@ func (r *KeaClusterReconciler) podTemplate(c *v1alpha1.KeaCluster, image, hash s
 	agent := corev1.Container{
 		Name:      kea.ContainerCtrlAgent,
 		Image:     image,
-		Command:   []string{"/bin/sh", kea.ConfigDir + "/entrypoint-ctrlagent.sh"},
+		Command:   []string{kea.CtrlAgentBin, "-c", kea.CtrlAgentConfPath},
 		Resources: c.Spec.Resources,
 		Ports: []corev1.ContainerPort{
 			{Name: "ctrl", ContainerPort: kea.CtrlAgentPort, Protocol: corev1.ProtocolTCP},
@@ -320,15 +331,35 @@ func (r *KeaClusterReconciler) podTemplate(c *v1alpha1.KeaCluster, image, hash s
 			Annotations: map[string]string{"kea.unkin.net/config-hash": hash},
 		},
 		Spec: corev1.PodSpec{
-			Containers:   []corev1.Container{dhcp4, agent},
-			Volumes:      []corev1.Volume{volProjected, volRun},
-			NodeSelector: c.Spec.NodeSelector,
-			Tolerations:  c.Spec.Tolerations,
-			Affinity:     c.Spec.Affinity,
+			InitContainers: []corev1.Container{initC},
+			Containers:     []corev1.Container{dhcp4, agent},
+			Volumes:        []corev1.Volume{volProjected, volRun},
+			NodeSelector:   c.Spec.NodeSelector,
+			Tolerations:    c.Spec.Tolerations,
+			Affinity:       c.Spec.Affinity,
 		},
 	}
 }
 
+// initEnv is the environment the embedded init.sh reads. Passing paths and
+// tunables as env vars (rather than interpolating them into the script text)
+// keeps init.sh static, committed and shellcheck-clean.
+func initEnv() []corev1.EnvVar {
+	return []corev1.EnvVar{
+		{Name: kea.EnvPodName, ValueFrom: &corev1.EnvVarSource{
+			FieldRef: &corev1.ObjectFieldSelector{FieldPath: "metadata.name"},
+		}},
+		{Name: kea.EnvRunDir, Value: kea.RunDir},
+		{Name: kea.EnvConfigDir, Value: kea.ConfigDir},
+		{Name: kea.EnvThisServerPlaceholder, Value: kea.ThisServerPlaceholder},
+		{Name: kea.EnvDHCP4Bin, Value: kea.DHCP4Bin},
+		{Name: kea.EnvDHCP4Conf, Value: kea.DHCP4ConfPath},
+		{Name: kea.EnvCtrlAgentConf, Value: kea.CtrlAgentConfPath},
+		{Name: kea.EnvWaitAttempts, Value: strconv.Itoa(kea.WaitAttempts)},
+		{Name: kea.EnvWaitSleep, Value: strconv.Itoa(kea.WaitSleepSeconds)},
+	}
+}
+
 // reloadReadyPods best-effort hot-reloads config on ready pods via the
 // ctrl-agent REST channel, analogous to bind-operator's rndc reconfig.
 func (r *KeaClusterReconciler) reloadReadyPods(ctx context.Context, c *v1alpha1.KeaCluster) {

internal/controller/keacluster_test.go

@@ -91,6 +91,95 @@ func TestKeaClusterReconcileCreatesWorkload(t *testing.T) {
 	}
 }
 
+// TestReconcileWiresInitContainer asserts the entrypoint refactor's pod shape:
+// a kea-init initContainer prepares config + waits for HA peer DNS, and the two
+// main containers exec kea directly with no wrapper shell. The init script comes
+// from the ConfigMap (so its hash rolls the STS), and the old per-container
+// entrypoint scripts are gone.
+func TestReconcileWiresInitContainer(t *testing.T) {
+	scheme := testScheme(t)
+	cluster := newClusterFixture()
+	cl := fake.NewClientBuilder().
+		WithScheme(scheme).
+		WithStatusSubresource(&v1alpha1.KeaCluster{}).
+		WithObjects(cluster).
+		Build()
+	r := &KeaClusterReconciler{Client: cl, Scheme: scheme}
+	if _, err := r.Reconcile(context.Background(), ctrl.Request{NamespacedName: types.NamespacedName{Namespace: "dhcp-system", Name: "pxe"}}); err != nil {
+		t.Fatalf("reconcile: %v", err)
+	}
+
+	// ConfigMap carries init.sh and no longer the per-container entrypoints.
+	var cm corev1.ConfigMap
+	if err := cl.Get(context.Background(), types.NamespacedName{Namespace: "dhcp-system", Name: "pxe-config"}, &cm); err != nil {
+		t.Fatalf("configmap not created: %v", err)
+	}
+	if cm.Data["init.sh"] == "" {
+		t.Errorf("configmap missing init.sh")
+	}
+	for _, gone := range []string{"entrypoint-dhcp4.sh", "entrypoint-ctrlagent.sh"} {
+		if _, ok := cm.Data[gone]; ok {
+			t.Errorf("configmap must not still carry %q", gone)
+		}
+	}
+
+	var sts appsv1.StatefulSet
+	if err := cl.Get(context.Background(), types.NamespacedName{Namespace: "dhcp-system", Name: "pxe"}, &sts); err != nil {
+		t.Fatalf("statefulset not created: %v", err)
+	}
+	spec := sts.Spec.Template.Spec
+
+	// Exactly one initContainer, named kea-init, running init.sh with POD_NAME
+	// sourced from the downward API.
+	if len(spec.InitContainers) != 1 || spec.InitContainers[0].Name != "kea-init" {
+		t.Fatalf("expected one kea-init initContainer, got %#v", spec.InitContainers)
+	}
+	initC := spec.InitContainers[0]
+	if got := initC.Command; len(got) != 2 || got[0] != "/bin/sh" || got[1] != "/etc/kea-operator/init.sh" {
+		t.Errorf("init command = %v, want [/bin/sh /etc/kea-operator/init.sh]", got)
+	}
+	var podNameFromDownward bool
+	for _, e := range initC.Env {
+		if e.Name == "POD_NAME" && e.ValueFrom != nil && e.ValueFrom.FieldRef != nil && e.ValueFrom.FieldRef.FieldPath == "metadata.name" {
+			podNameFromDownward = true
+		}
+	}
+	if !podNameFromDownward {
+		t.Errorf("init container must source POD_NAME from downward API metadata.name, env=%#v", initC.Env)
+	}
+
+	// Main containers exec kea directly (no /bin/sh wrapper).
+	wantCmd := map[string][]string{
+		"kea-dhcp4":      {"/usr/sbin/kea-dhcp4", "-c", "/var/run/kea/kea-dhcp4.conf"},
+		"kea-ctrl-agent": {"/usr/sbin/kea-ctrl-agent", "-c", "/var/run/kea/kea-ctrl-agent.conf"},
+	}
+	for _, ctr := range spec.Containers {
+		want, ok := wantCmd[ctr.Name]
+		if !ok {
+			t.Errorf("unexpected container %q", ctr.Name)
+			continue
+		}
+		if len(ctr.Command) == 0 || ctr.Command[0] == "/bin/sh" {
+			t.Errorf("container %q must exec kea directly, got %v", ctr.Name, ctr.Command)
+		}
+		if !equalStrings(ctr.Command, want) {
+			t.Errorf("container %q command = %v, want %v", ctr.Name, ctr.Command, want)
+		}
+	}
+}
+
+func equalStrings(a, b []string) bool {
+	if len(a) != len(b) {
+		return false
+	}
+	for i := range a {
+		if a[i] != b[i] {
+			return false
+		}
+	}
+	return true
+}
+
 // TestConfigHashChangesWithSubnets guards the roll trigger: adding a subnet
 // must change the pod-template config hash (so the STS rolls).
 func TestConfigHashChangesWithSubnets(t *testing.T) {

internal/kea/agent.go

@@ -1,6 +1,6 @@
 package kea
 
-import "fmt"
+import _ "embed"
 
 type ctrlAgentRoot struct {
 	ControlAgent controlAgent `json:"Control-agent"`
@@ -27,36 +27,15 @@ func RenderCtrlAgent() (string, error) {
 	}})
 }
 
-// EntrypointDHCP4 is the kea-dhcp4 container entrypoint. It derives this pod's
-// HA peer name from the StatefulSet ordinal, substitutes the placeholder in the
-// projected config, and execs the server.
-func EntrypointDHCP4() string {
-	return fmt.Sprintf(`#!/bin/sh
-set -e
-ORD="${HOSTNAME##*-}"
-mkdir -p %[1]s
-chmod 0750 %[1]s
-sed "s/%[2]s/server${ORD}/g" %[3]s/kea-dhcp4.conf > %[4]s
-# The HA hook resolves peer URL hostnames once at load; on a cold container
-# start the StatefulSet peer DNS records may not resolve yet, and kea exits
-# hard instead of retrying. Wait for the config to validate before starting.
-i=0
-until %[5]s -t %[4]s >/dev/null 2>&1; do
-  i=$((i+1))
-  if [ "$i" -ge 60 ]; then break; fi
-  sleep 2
-done
-exec %[5]s -c %[4]s
-`, RunDir, ThisServerPlaceholder, ConfigDir, DHCP4ConfPath, DHCP4Bin)
-}
+// initScript is the initContainer entrypoint. It is a committed, shellcheck-clean
+// shell file (no fmt.Sprintf interpolation) parameterised entirely by the
+// environment variables the operator sets on the initContainer. It prepares the
+// shared run dir, finalises this pod's kea-dhcp4 config from the StatefulSet
+// ordinal, and bounded-waits for the HA peer DNS to resolve before the main
+// kea-dhcp4 / kea-ctrl-agent containers exec kea directly.
+//
+//go:embed scripts/init.sh
+var initScript string
 
-// EntrypointCtrlAgent is the kea-ctrl-agent container entrypoint.
-func EntrypointCtrlAgent() string {
-	return fmt.Sprintf(`#!/bin/sh
-set -e
-mkdir -p %[1]s
-chmod 0750 %[1]s
-cp %[2]s/kea-ctrl-agent.conf %[3]s
-exec %[4]s -c %[3]s
-`, RunDir, ConfigDir, CtrlAgentConfPath, CtrlAgentBin)
-}
+// InitScript returns the initContainer entrypoint shell script.
+func InitScript() string { return initScript }

internal/kea/config_test.go

@@ -237,29 +237,44 @@ func TestRenderCtrlAgent(t *testing.T) {
 	}
 }
 
-func TestEntrypointsHardenSocketDir(t *testing.T) {
+func TestInitScriptHardensSocketDir(t *testing.T) {
 	// Kea 2.6+ rejects a socket dir "more relaxed than 750"; the emptyDir mount
-	// defaults to 0777, so the entrypoints must chmod it before exec'ing kea.
-	want := "chmod 0750 " + RunDir
-	if ep := EntrypointDHCP4(); !strings.Contains(ep, want) {
-		t.Errorf("dhcp4 entrypoint must %q, got:\n%s", want, ep)
-	}
-	if ep := EntrypointCtrlAgent(); !strings.Contains(ep, want) {
-		t.Errorf("ctrl-agent entrypoint must %q, got:\n%s", want, ep)
+	// defaults to 0777, so the initContainer must chmod it (via $RUN_DIR) before
+	// the main containers exec kea.
+	if s := InitScript(); !strings.Contains(s, `chmod 0750 "$RUN_DIR"`) {
+		t.Errorf("init script must chmod 0750 the run dir, got:\n%s", s)
 	}
 }
 
-func TestEntrypointWaitsForConfigToValidate(t *testing.T) {
-	// The dhcp4 entrypoint must gate startup on `kea-dhcp4 -t` so a cold-start
-	// HA peer DNS resolution failure retries instead of crash-looping.
-	ep := EntrypointDHCP4()
-	for _, want := range []string{"until " + DHCP4Bin + " -t " + DHCP4ConfPath, "exec " + DHCP4Bin + " -c " + DHCP4ConfPath} {
-		if !strings.Contains(ep, want) {
-			t.Errorf("dhcp4 entrypoint must contain %q, got:\n%s", want, ep)
+func TestInitScriptWaitsForConfigToValidate(t *testing.T) {
+	// The init script must gate startup on `kea-dhcp4 -t` so a cold-start HA peer
+	// DNS resolution failure retries (bounded) instead of crash-looping, and must
+	// fail loud after the cap so the kubelet restarts the initContainer.
+	s := InitScript()
+	for _, want := range []string{
+		`until "$DHCP4_BIN" -t "$DHCP4_CONF"`,
+		`"$i" -ge "$WAIT_ATTEMPTS"`,
+		"exit 1",
+	} {
+		if !strings.Contains(s, want) {
+			t.Errorf("init script must contain %q, got:\n%s", want, s)
 		}
 	}
 }
 
+func TestInitScriptIsInterpolationFree(t *testing.T) {
+	// The whole point of the refactor: the script is a static embedded file, not
+	// a Go-interpolated string. It must carry no fmt verbs and must derive the
+	// HA peer name from the pod ordinal via $POD_NAME.
+	s := InitScript()
+	if strings.Contains(s, "%[") || strings.Contains(s, "%s") || strings.Contains(s, "%d") {
+		t.Errorf("init script must not contain fmt verbs:\n%s", s)
+	}
+	if !strings.Contains(s, `ord="${POD_NAME##*-}"`) {
+		t.Errorf("init script must derive the ordinal from $POD_NAME, got:\n%s", s)
+	}
+}
+
 func TestControlSocketPathAllowedByKea(t *testing.T) {
 	if !strings.HasPrefix(CtrlSocketPath, "/var/run/kea/") {
 		t.Errorf("CtrlSocketPath %q must live under /var/run/kea (kea 2.6+ restriction)", CtrlSocketPath)

internal/kea/consts.go

@@ -7,6 +7,9 @@ const (
 	ContainerDHCP4 = "kea-dhcp4"
 	// ContainerCtrlAgent is the kea-ctrl-agent container name.
 	ContainerCtrlAgent = "kea-ctrl-agent"
+	// ContainerInit is the initContainer that finalises config and waits for
+	// HA peer DNS before the main containers start.
+	ContainerInit = "kea-init"
 
 	// ConfigDir is where projected config is mounted read-only.
 	ConfigDir = "/etc/kea-operator"
@@ -22,8 +25,9 @@ const (
 	CtrlAgentConfPath = RunDir + "/kea-ctrl-agent.conf"
 	// CtrlSocketPath is the unix control socket between ctrl-agent and dhcp4.
 	CtrlSocketPath = RunDir + "/kea4-ctrl-socket"
-	// EntrypointPath is the generated container entrypoint.
-	EntrypointPath = ConfigDir + "/entrypoint.sh"
+	// InitScriptPath is where the initContainer entrypoint is projected from the
+	// ConfigMap.
+	InitScriptPath = ConfigDir + "/init.sh"
 
 	// DHCP4Bin is the kea-dhcp4 server binary.
 	DHCP4Bin = "/usr/sbin/kea-dhcp4"
@@ -47,4 +51,35 @@ const (
 
 	// ClientArchOption is the DHCP option code carrying PXE client arch.
 	ClientArchOption = 93
+
+	// WaitAttempts caps the initContainer's bounded wait for the HA peer DNS to
+	// resolve (i.e. for the rendered config to pass "kea-dhcp4 -t").
+	WaitAttempts = 60
+	// WaitSleepSeconds is the delay between bounded-wait attempts.
+	WaitSleepSeconds = 2
+)
+
+// Environment variable names the operator sets on the initContainer. The
+// embedded init.sh reads only these; keeping the names here means the script
+// stays free of any Go string interpolation.
+const (
+	// EnvPodName carries the pod name (downward API metadata.name); its ordinal
+	// suffix selects this pod's HA peer name.
+	EnvPodName = "POD_NAME"
+	// EnvRunDir is the shared run/socket dir path.
+	EnvRunDir = "RUN_DIR"
+	// EnvConfigDir is the read-only projected config dir path.
+	EnvConfigDir = "CONFIG_DIR"
+	// EnvThisServerPlaceholder is the token replaced with this pod's HA peer name.
+	EnvThisServerPlaceholder = "THIS_SERVER_PLACEHOLDER"
+	// EnvDHCP4Bin is the kea-dhcp4 binary path (used for the -t config check).
+	EnvDHCP4Bin = "DHCP4_BIN"
+	// EnvDHCP4Conf is the finalized kea-dhcp4 config path in the shared run dir.
+	EnvDHCP4Conf = "DHCP4_CONF"
+	// EnvCtrlAgentConf is the staged kea-ctrl-agent config path in the run dir.
+	EnvCtrlAgentConf = "CTRL_AGENT_CONF"
+	// EnvWaitAttempts is the bounded-wait attempt cap.
+	EnvWaitAttempts = "WAIT_ATTEMPTS"
+	// EnvWaitSleep is the per-attempt sleep in seconds.
+	EnvWaitSleep = "WAIT_SLEEP"
 )

internal/kea/scripts/init.sh

@@ -0,0 +1,41 @@
+#!/bin/sh
+# kea-operator initContainer.
+#
+# Prepares the shared run dir, finalises this pod's kea-dhcp4 config (the HA
+# this-server-name is derived from the StatefulSet ordinal, known only at pod
+# start), and waits for the HA peer DNS to resolve before the main kea
+# containers start. Every input arrives as an environment variable set by the
+# operator; nothing is interpolated into this file, so it is shellcheck-clean
+# and testable on its own.
+set -eu
+
+# StatefulSet pod names are "<sts>-<ordinal>"; the ordinal is this HA peer's id.
+ord="${POD_NAME##*-}"
+
+# The run dir is a shared emptyDir. Kea 2.6+ refuses a control socket in a
+# world-accessible directory, so tighten it to 0750.
+mkdir -p "$RUN_DIR"
+chmod 0750 "$RUN_DIR"
+
+# Finalise the per-pod dhcp4 config: substitute this pod's HA peer name into the
+# shared (pod-independent) config projected from the ConfigMap.
+sed "s/${THIS_SERVER_PLACEHOLDER}/server${ord}/g" \
+	"${CONFIG_DIR}/kea-dhcp4.conf" >"$DHCP4_CONF"
+
+# The ctrl-agent config is pod-independent; stage it in the shared run dir so
+# the main container can exec kea directly with no wrapper.
+cp "${CONFIG_DIR}/kea-ctrl-agent.conf" "$CTRL_AGENT_CONF"
+
+# The HA hook resolves peer URL hostnames once at load; on a cold start the
+# StatefulSet peer DNS records may not resolve yet and kea exits hard instead of
+# retrying. Wait (bounded) for the config to validate, then fail loud so the
+# kubelet restarts this initContainer rather than starting a doomed server.
+i=0
+until "$DHCP4_BIN" -t "$DHCP4_CONF" >/dev/null 2>&1; do
+	i=$((i + 1))
+	if [ "$i" -ge "$WAIT_ATTEMPTS" ]; then
+		echo "kea-init: config failed to validate after ${WAIT_ATTEMPTS} attempts" >&2
+		exit 1
+	fi
+	sleep "$WAIT_SLEEP"
+done