deploy: Add warm-cache CronJob

- Introduced a new `warm-cache` CronJob to periodically preload the cache.
- Added supporting scripts (`warm-cache.sh`, `warm-cache-init.sh`) to manage the cache warm-up process.
- Configured `ServiceAccount` for the frontend deployment to enhance security.
- Adjusted HPA minimum replicas from 1 to 2 for better availability.
- Set frontend deployment to use debug log level.

Signed-off-by: Stefan Prodan <stefan.prodan@gmail.com>

deploy/bases/frontend/cronjob-warm-cache.yaml

@@ -0,0 +1,68 @@
+apiVersion: batch/v1
+kind: CronJob
+metadata:
+  name: warm-cache
+spec:
+  # Runs every 5 minutes
+  schedule: "*/5 * * * *"
+  concurrencyPolicy: Forbid
+  successfulJobsHistoryLimit: 1
+  failedJobsHistoryLimit: 1
+  jobTemplate:
+    spec:
+      # Cleanup after 1 hour
+      ttlSecondsAfterFinished: 3600
+      backoffLimit: 3
+      template:
+        metadata:
+          labels:
+            app.kubernetes.io/name: warm-cache
+            app.kubernetes.io/part-of: frontend
+        spec:
+          serviceAccountName: frontend
+          restartPolicy: OnFailure
+          initContainers:
+          - name: warm-cache-init
+            image: ghcr.io/stefanprodan/podinfo:6.13.0
+            imagePullPolicy: IfNotPresent
+            command:
+            - /bin/sh
+            - /scripts/warm-cache-init.sh
+            env:
+            - name: FRONTEND_URL
+              value: "http://frontend"
+            resources:
+              limits:
+                cpu: 100m
+                memory: 32Mi
+              requests:
+                cpu: 10m
+                memory: 16Mi
+            volumeMounts:
+            - name: scripts
+              mountPath: /scripts
+          containers:
+          - name: warm-cache
+            image: ghcr.io/stefanprodan/podinfo:6.13.0
+            imagePullPolicy: IfNotPresent
+            command:
+            - /bin/sh
+            - /scripts/warm-cache.sh
+            env:
+            - name: FRONTEND_URL
+              value: "http://frontend"
+            resources:
+              limits:
+                cpu: 100m
+                memory: 32Mi
+              requests:
+                cpu: 10m
+                memory: 16Mi
+            volumeMounts:
+            - name: scripts
+              mountPath: /scripts
+          volumes:
+          - name: scripts
+            configMap:
+              name: warm-cache-script
+              defaultMode: 0755

deploy/bases/frontend/deployment.yaml

@@ -21,6 +21,7 @@ spec:
       labels:
         app.kubernetes.io/name: frontend
     spec:
+      serviceAccountName: frontend
       containers:
       - name: frontend
         image: ghcr.io/stefanprodan/podinfo:6.13.0
@@ -39,7 +40,7 @@ spec:
         - ./podinfo
         - --port=9898
         - --port-metrics=9797
-        - --level=info
+        - --level=debug
         - --backend-url=http://backend:9898/echo
         - --cache-server=tcp://cache:6379
         env:

deploy/bases/frontend/hpa.yaml

@@ -7,7 +7,7 @@ spec:
     apiVersion: apps/v1
     kind: Deployment
     name: frontend
-  minReplicas: 1
+  minReplicas: 2
   maxReplicas: 4
   metrics:
   - type: Resource

deploy/bases/frontend/kustomization.yaml

@@ -1,7 +1,15 @@
 apiVersion: kustomize.config.k8s.io/v1beta1
 kind: Kustomization
 resources:
+  - serviceaccount.yaml
   - service.yaml
   - deployment.yaml
   - hpa.yaml
-
+  - cronjob-warm-cache.yaml
+configMapGenerator:
+  - name: warm-cache-script
+    files:
+      - scripts/warm-cache.sh
+      - scripts/warm-cache-init.sh
+    options:
+      disableNameSuffixHash: true

deploy/bases/frontend/scripts/warm-cache-init.sh

@@ -0,0 +1,13 @@
+#!/bin/sh
+set -e
+
+# Init step for the warm-cache job.
+# Calls the frontend in verbose mode so the full connection, request and
+# response debug data (DNS, TCP, headers, timings) is dumped to the logs.
+
+FRONTEND="${FRONTEND_URL:-http://frontend}"
+
+echo "Dumping debug data for ${FRONTEND}/api/info"
+# -v writes the verbose debug data to stderr, redirect it to stdout so it
+# lands in the container logs together with the response body.
+curl -v "${FRONTEND}/api/info" 2>&1

deploy/bases/frontend/scripts/warm-cache.sh

@@ -0,0 +1,69 @@
+#!/bin/sh
+set -e
+
+# This is a simulation of a cache warming process.
+# It fetches the frontend info, stores it in the cache under the job pod
+# hostname and reads it back to verify the round-trip.
+#
+# Log lines mimic the Log4j 2 default PatternLayout:
+#   %d{yyyy-MM-dd HH:mm:ss,SSS} [%thread] %-5level %logger{36} - %msg
+
+LOGGER="com.stefanprodan.podinfo.WarmCache"
+THREAD="main"
+
+log() {
+  level="$1"
+  shift
+  # millisecond precision timestamp; fall back gracefully if %N is unsupported
+  ts="$(date '+%Y-%m-%d %H:%M:%S,%N' 2>/dev/null)"
+  case "$ts" in
+    *%N|*,) ts="$(date '+%Y-%m-%d %H:%M:%S'),000" ;;
+    *) ts="$(echo "$ts" | cut -c1-23)" ;;
+  esac
+  printf '%s [%s] %-5s %s - %s\n' "$ts" "$THREAD" "$level" "$LOGGER" "$*"
+}
+
+FRONTEND="${FRONTEND_URL:-http://frontend}"
+KEY="$(hostname)"
+START="$(date +%s)"
+
+log INFO "Fetching info from ${FRONTEND}/api/info"
+# Compact the (pretty-printed) JSON onto a single line so each log event
+# stays on one line, as Log4j renders them.
+INFO="$(curl -fsS "${FRONTEND}/api/info" | tr -d '\n' | sed 's/  */ /g')"
+log INFO "Info: ${INFO}"
+
+# Log each field of the info response on its own line. The /api/info payload
+# is a flat JSON object of string values, so we can split it without jq.
+echo "$INFO" | sed 's/^{//; s/}$//' | tr ',' '\n' | while IFS= read -r field; do
+  field="$(echo "$field" | sed 's/^[[:space:]]*//; s/[[:space:]]*$//; s/"//g')"
+  if [ -n "$field" ]; then
+    log DEBUG "info ${field}"
+  fi
+done
+
+log INFO "Writing info to cache key ${KEY}"
+curl -fsS -X POST -H "Content-Type: application/json" -d "${INFO}" "${FRONTEND}/cache/${KEY}"
+
+# Verify the cached value for 1 minute, polling every 10 seconds.
+attempt=1
+while [ "$attempt" -le 6 ]; do
+  log INFO "Reading cache key ${KEY} (attempt ${attempt}/6)"
+  CACHED="$(curl -fsS "${FRONTEND}/cache/${KEY}")"
+
+  if [ "${INFO}" = "${CACHED}" ]; then
+    log INFO "Cache warm verified: cached value matches info"
+  else
+    log ERROR "Cache warm failed: cached value does not match info"
+    log ERROR "Expected: ${INFO}"
+    log ERROR "Got:      ${CACHED}"
+    exit 1
+  fi
+
+  attempt=$((attempt + 1))
+  if [ "$attempt" -le 6 ]; then
+    sleep 10
+  fi
+done
+
+log INFO "Cache warm finished in $(( $(date +%s) - START ))s"

deploy/bases/frontend/serviceaccount.yaml

@@ -0,0 +1,4 @@
+apiVersion: v1
+kind: ServiceAccount
+metadata:
+  name: frontend