Sizing Tool: Set the minimum replias to 3. (#8329)

pkg/sizing/algorithm.go

@@ -28,6 +28,9 @@ func calculateClusterSize(nt NodeType, bytesDayIngest float64, qperf QueryPerf)
 	bytesSecondIngest := bytesDayIngest / 86400
 	numWriteReplicasNeeded := math.Ceil(bytesSecondIngest / nt.writePod.rateBytesSecond)
 
+	// High availability requires at least 3 replicas.
+	numWriteReplicasNeeded = math.Max(3, numWriteReplicasNeeded)
+
 	//Hack based on current 4-1 mem to cpu ratio and base machine w/ 4 cores and 1 write/read
 	writeReplicasPerNode := float64(nt.cores / 4)
 	fullyWritePackedNodes := math.Floor(numWriteReplicasNeeded / writeReplicasPerNode)
@@ -61,6 +64,10 @@ func calculateClusterSize(nt NodeType, bytesDayIngest float64, qperf QueryPerf)
 	actualReadReplicasAdded := actualNodesAddedForReads * readReplicasPerEmptyNode
 
 	totalReadReplicas := actualReadReplicasAdded + baselineReadReplicas
+
+	// High availability requires at least 3 replicas.
+	totalReadReplicas = math.Max(3, totalReadReplicas)
+
 	totalReadThroughputBytesSec := totalReadReplicas * nt.readPod.rateBytesSecond
 
 	totalNodesNeeded := nodesNeededForWrites + actualNodesAddedForReads

pkg/sizing/algorithm_test.go

@@ -50,3 +50,17 @@ func Test_CoresNodeInvariant(t *testing.T) {
 		}
 	}
 }
+
+func Test_MinimumReplicas(t *testing.T) {
+	for _, queryPerformance := range []QueryPerf{Basic, Super} {
+		for _, ingest := range []float64{1, 1000} {
+			for _, cloud := range NodeTypesByProvider {
+				for _, node := range cloud {
+					size := calculateClusterSize(node, ingest, queryPerformance)
+					require.GreaterOrEqual(t, size.TotalReadReplicas, 3)
+					require.GreaterOrEqual(t, size.TotalWriteReplicas, 3)
+				}
+			}
+		}
+	}
+}