redis-ha: fix readiness probe for non-connected slaves (#293)

When Redis is running as a slave, don't pass readiness probes until and
unless the replica is fully synchronised.

This resolves the issue where, when Redis is upgraded, the replica is
marked ready while still syncing from the master. This can lead to the
master pod being terminated and restarted with no slaves ready to take
over from it, leaving the Redis cluster failed until the original
primary comes back up again.

Signed-off-by: Chris Boot <[email protected]>
Co-authored-by: Aaron Layfield <[email protected]>

charts/redis-ha/Chart.yaml

@@ -5,7 +5,7 @@ keywords:
 - redis
 - keyvalue
 - database
-version: 4.28.0
+version: 4.28.1
 appVersion: 7.2.4
 description: This Helm chart provides a highly available Redis implementation with a master/slave configuration and uses Sentinel sidecars for failover management
 icon: https://upload.wikimedia.org/wikipedia/en/thumb/6/6b/Redis_Logo.svg/1200px-Redis_Logo.svg.png

charts/redis-ha/templates/_configs.tpl

@@ -669,10 +669,39 @@
         ping
     )
     if [ "$response" != "PONG" ] ; then
-      echo "$response"
+      echo "ping=$response"
+      exit 1
+    fi
+
+    response=$(
+      redis-cli \
+      {{- if .Values.auth }}
+        -a "${AUTH}" --no-auth-warning \
+      {{- end }}
+        -h localhost \
+      {{- if ne (int .Values.redis.port) 0 }}
+        -p {{ .Values.redis.port }} \
+      {{- else }}
+        -p {{ .Values.redis.tlsPort }} ${TLS_CLIENT_OPTION} \
+      {{- end}}
+        role
+    )
+    role=$( echo "$response" | sed "1!d" )
+    if [ "$role" = "master" ]; then
+      echo "role=$role"
+      exit 0
+    elif [ "$role" = "slave" ]; then
+      repl=$( echo "$response" | sed "4!d" )
+      echo "role=$role; repl=$repl"
+      if [ "$repl" = "connected" ]; then
+        exit 0
+      else
+        exit 1
+      fi
+    else
+      echo "role=$role"
       exit 1
     fi
-    echo "response=$response"
 {{- end }}
 
 {{- define "sentinel_liveness.sh" }}