Adds an entry for Redis in the FAQ (#6231)

* Adds an entry for Redis in the FAQ

Addresses: issue https://github.com/istio/istio/issues/16078

* Copy edits

Co-authored-by: Adam Miller <1402860+adammil2000@users.noreply.github.com>

content/en/faq/applications/redis.md

@@ -0,0 +1,32 @@
+---
+title: Can I run Redis inside an Istio mesh?
+description: How to run Redis with Istio.
+weight: 50
+keywords: [redis]
+---
+
+Similar to other services deployed in an Istio service mesh, Redis instances
+need to listen on `localhost` (`127.0.0.1`). However, each Redis slave instance
+should announce an address that can be used by master to reach it, which cannot
+also be `localhost` (`127.0.0.1`).
+
+Use the Redis configuration parameter `replica-announce-ip` to announce the
+correct address.  For example, set `replica-announce-ip` to the IP address of
+each Redis slave instance using these steps:
+
+Pass the pod IP address through an environment variable in the `env` subsection
+of the slave `StatefulSet` definition:
+
+{{< text yaml >}}
+    - name: "POD_IP"
+      valueFrom:
+        fieldRef:
+          fieldPath: status.podIP
+{{< /text >}}
+
+Also, add the following under the `command` subsection:
+
+{{< text yaml >}}
+echo "" >> /opt/bitnami/redis/etc/replica.conf
+echo "replica-announce-ip $POD_IP" >> /opt/bitna
+{{< /text >}}