docs: B-5 — the pod stays Ready while every request hangs

Stopping Redis returns HTTP 000 rather than an error because the client waits on reconnect, and the pod keeps serving traffic because the redis health indicator is not in the readiness group even though /actuator/health returns 503. That is the mirror image of A-2, where Keycloak put its database check in readiness and the pods left the Service.

Turning on AOF with config set created the appendonlydir and still lost everything on pod deletion, because /data was the container filesystem; adding a PVC makes the same setting work. Volume first, persistence setting second.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

deploy/lab/k8s/bff-redis.yaml

@@ -24,9 +24,24 @@ stringData:
   # Base64 in etcd is not encryption — see D-3.
   KEYCLOAK_CLIENT_SECRET: bff-lab-secret
 ---
-# Redis. No persistence yet: `--save ""` and no appendonly, so a restart loses
-# everything. B-5 and B-6 compare that against RDB and AOF, which is easier to
-# reason about when the starting point is "nothing survives".
+# Redis. B-5 measured that turning on AOF with `redis-cli config set` changes
+# nothing here, because /data is the container filesystem and dies with the
+# container — the appendonlydir was created and then thrown away. Persistence
+# configuration without a volume is decoration.
+#
+# So the volume comes first, and only then does `--appendonly yes` mean anything.
+apiVersion: v1
+kind: PersistentVolumeClaim
+metadata:
+  name: redis-data
+  namespace: keycloak-lab
+spec:
+  accessModes: [ReadWriteOnce]
+  storageClassName: local-path
+  resources:
+    requests:
+      storage: 1Gi
+---
 apiVersion: apps/v1
 kind: Deployment
 metadata:
@@ -47,16 +62,25 @@ spec:
       containers:
         - name: redis
           image: redis:7.4-alpine
-          args: ["redis-server", "--save", "", "--appendonly", "no"]
+          # appendfsync everysec 이 기본값이다 — 1초 분량을 잃을 수 있다.
+          # Keycloak 의 synchronous_commit OFF(A-3)와 같은 모양의 트레이드오프다.
+          args: ["redis-server", "--appendonly", "yes", "--dir", "/data"]
           ports:
             - containerPort: 6379
               name: redis
           readinessProbe:
             exec: { command: ["redis-cli", "ping"] }
             initialDelaySeconds: 3
+          volumeMounts:
+            - name: data
+              mountPath: /data
           resources:
             requests: { memory: 32Mi, cpu: 20m }
             limits:   { memory: 128Mi }
+      volumes:
+        - name: data
+          persistentVolumeClaim:
+            claimName: redis-data
 ---
 apiVersion: v1
 kind: Service