From 269233913800a51bdc0ef3eba6de1da13107b8fc Mon Sep 17 00:00:00 2001
From: antirez <antirez@gmail.com>
Date: Mon, 12 May 2014 16:34:20 +0200
Subject: [PATCH] Cluster: forced failover implemented.

Using CLUSTER FAILOVER FORCE it is now possible to failover a master in
a forced way, which means:

1) No check to understand if the master is up is performed.
2) No data age of the slave is checked. Evan a slave with very old data
   can manually failover a master in this way.
3) No chat with the master is attempted to reach its replication offset:
   the master can just be down.
---
 src/cluster.c | 32 +++++++++++++++++++++++++++-----
 1 file changed, 27 insertions(+), 5 deletions(-)

diff --git a/src/cluster.c b/src/cluster.c
index 70ad7ab7..6ce6a3d1 100644
--- a/src/cluster.c
+++ b/src/cluster.c
@@ -3646,13 +3646,27 @@ void clusterCommand(redisClient *c) {
             addReplyBulkCString(c,ni);
             sdsfree(ni);
         }
-    } else if (!strcasecmp(c->argv[1]->ptr,"failover") && c->argc == 2) {
-        /* CLUSTER FAILOVER */
+    } else if (!strcasecmp(c->argv[1]->ptr,"failover") &&
+               (c->argc == 2 || c->argc == 3))
+    {
+        /* CLUSTER FAILOVER [FORCE] */
+        int force = 0;
+
+        if (c->argc == 3) {
+            if (!strcasecmp(c->argv[2]->ptr,"force")) {
+                force = 1;
+            } else {
+                addReply(c,shared.syntaxerr);
+                return;
+            }
+        }
+
         if (nodeIsMaster(myself)) {
             addReplyError(c,"You should send CLUSTER FAILOVER to a slave");
             return;
-        } else if (myself->slaveof == NULL || nodeFailed(myself->slaveof) ||
-                   myself->slaveof->link == NULL)
+        } else if (!force &&
+                   (myself->slaveof == NULL || nodeFailed(myself->slaveof) ||
+                   myself->slaveof->link == NULL))
         {
             addReplyError(c,"Master is down or failed, "
                             "please use CLUSTER FAILOVER FORCE");
@@ -3660,7 +3674,15 @@ void clusterCommand(redisClient *c) {
         }
         resetManualFailover();
         server.cluster->mf_end = mstime() + REDIS_CLUSTER_MF_TIMEOUT;
-        clusterSendMFStart(myself->slaveof);
+
+        /* If this is a forced failover, we don't need to talk with our master
+         * to agree about the offset. We just failover taking over it without
+         * coordination. */
+        if (force) {
+            server.cluster->mf_can_start = 1;
+        } else {
+            clusterSendMFStart(myself->slaveof);
+        }
         redisLog(REDIS_WARNING,"Manual failover user request accepted.");
         addReply(c,shared.ok);
     } else if (!strcasecmp(c->argv[1]->ptr,"set-config-epoch") && c->argc == 3)