Cluster: error out quicker if port is unusable

The default cluster control port is 10,000 ports higher than
the base Redis port.  If Redis is started on a too-high port,
Cluster can't start and everything will exit later anyway.

1 files changed, 13 insertions, 0 deletions

diff --git a/src/cluster.c b/src/cluster.c
index afea589ec..15afd8e54 100644
--- a/src/cluster.c
+++ b/src/cluster.c
@@ -329,6 +329,19 @@ void clusterInit(void) {
 
     /* We need a listening TCP port for our cluster messaging needs. */
     server.cfd_count = 0;
+
+    /* Port sanity check II
+       The other handshake port check is triggered too late to stop
+       us from trying to use a too-high cluster port number.
+    */
+    if (server.port > (65535-REDIS_CLUSTER_PORT_INCR)) {
+        redisLog(REDIS_WARNING, "Redis port number too high. "
+                   "Cluster communication port is 10,000 port "
+                   "numbers higher than your Redis port. "
+                   "Your Redis port number must be "
+                   "lower than 55535.");
+    }
+
     if (listenToPort(server.port+REDIS_CLUSTER_PORT_INCR,
         server.cfd,&server.cfd_count) == REDIS_ERR)
     {