fix: Recycle connections in some Redis Cluster scenarios

This issue was surfaced in a Cloud Provider solution that used for
rolling out new nodes using the same address (hostname) of the nodes
that will be replaced in a Redis Cluster, while the former ones once
depromoted as Slaves would continue in service during some mintues
for redirecting traffic.

The solution basically identifies when the connection could be stale
since a MOVED response will be returned using the same address (hostname)
that is being used by the connection. At that moment we consider the
connection as no longer usable forcing to recycle the connection.

Author: pfreixes

error.go

@@ -65,7 +65,7 @@ func isRedisError(err error) bool {
 	return ok
 }
 
-func isBadConn(err error, allowTimeout bool) bool {
+func isBadConn(err error, allowTimeout bool, addr string) bool {
 	switch err {
 	case nil:
 		return false
@@ -74,9 +74,16 @@ func isBadConn(err error, allowTimeout bool) bool {
 	}
 
 	if isRedisError(err) {
-		// Close connections in read only state in case domain addr is used
-		// and domain resolves to a different Redis Server. See #790.
-		return isReadOnlyError(err)
+		if isReadOnlyError(err) {
+			// Close connections in read only state in case domain addr is used
+			// and domain resolves to a different Redis Server. See #790.
+			return true
+		} else if isMovedSameConnAddr(err, addr) {
+			// Close connections when we are asked to move to the same addr
+			// of the connection. Force a DNS resolution when all connections
+			// of the pool are recycled
+			return true
+		}
 	}
 
 	if allowTimeout {
@@ -119,6 +126,15 @@ func isReadOnlyError(err error) bool {
 	return strings.HasPrefix(err.Error(), "READONLY ")
 }
 
+func isMovedSameConnAddr(err error, addr string) bool {
+	redisError := err.Error()
+	if !strings.HasPrefix(redisError, "MOVED ") {
+		return false
+	}
+	return strings.HasSuffix(redisError, addr)
+}
+
+
 //------------------------------------------------------------------------------
 
 type timeoutError interface {

pubsub.go

@@ -141,7 +141,7 @@ func (c *PubSub) releaseConn(ctx context.Context, cn *pool.Conn, err error, allo
 	if c.cn != cn {
 		return
 	}
-	if isBadConn(err, allowTimeout) {
+	if isBadConn(err, allowTimeout, c.opt.Addr) {
 		c.reconnect(ctx, err)
 	}
 }

redis.go

@@ -261,7 +261,7 @@ func (c *baseClient) releaseConn(ctx context.Context, cn *pool.Conn, err error)
 		c.opt.Limiter.ReportResult(err)
 	}
 
-	if isBadConn(err, false) {
+	if isBadConn(err, false, c.opt.Addr) {
 		c.connPool.Remove(ctx, cn, err)
 	} else {
 		c.connPool.Put(ctx, cn)