[CLIENT-3156] Fix as issue where rack policy always returns the maste…

…r node

CHANGELOG.md

@@ -1,5 +1,12 @@
 # Change History
 
+## November 1 2024: v7.7.2
+
+  Minor fix release.
+
+- **Fixes**
+  - [CLIENT-3156] Fix an issue where rack policy always returns the master node. Resolves #455
+
 ## September 18 2024: v7.7.1
 
   Hot Fix release. This version fixes a major bug introduced in v7.7.0. You should use this release instead.

partition.go

@@ -249,21 +249,25 @@ func (ptn *Partition) getSequenceNode(cluster *Cluster) (*Node, Error) {
 func (ptn *Partition) getRackNode(cluster *Cluster) (*Node, Error) {
 	replicas := ptn.partitions.Replicas
 
+	// Try to find a node on the same rack first:
 	for _, rackId := range cluster.clientPolicy.RackIds {
 		seq := ptn.sequence
 		for range replicas {
-			index := ptn.sequence % len(replicas)
+			index := seq % len(replicas)
 			node := replicas[index][ptn.PartitionId]
 
 			if node != nil && node != ptn.prevNode && node.hasRack(ptn.Namespace, rackId) && node.IsActive() {
 				ptn.prevNode = node
-				ptn.sequence = seq
+				ptn.sequence = seq + 1 // start from the next node and save a comparison
 				return node, nil
 			}
 			seq++
 		}
 	}
 
+	// A node on the same Rack was not found, so try other options.
+	// Same node as the previous will be the last option,
+	// since it is the least desirable.
 	for range replicas {
 		index := ptn.sequence % len(replicas)
 		node := replicas[index][ptn.PartitionId]