Fix computation of ShuffleShardExpectedInstancesPerZone for math.MaxI…

…nt. (grafana#567)

ring/shard/shard.go

@@ -30,6 +30,9 @@ func ShuffleShardSeed(identifier, zone string) int64 {
 // zone when zone-aware replication is enabled. The algorithm expects the shard size to be divisible
 // by the number of zones, in order to have nodes balanced across zones. If it's not, we do round up.
 func ShuffleShardExpectedInstancesPerZone(shardSize, numZones int) int {
+	if shardSize == math.MaxInt {
+		return math.MaxInt
+	}
 	return int(math.Ceil(float64(shardSize) / float64(numZones)))
 }
 

ring/shard/shard_test.go

@@ -1,6 +1,7 @@
 package shard
 
 import (
+	"math"
 	"testing"
 
 	"github.com/stretchr/testify/assert"
@@ -38,6 +39,11 @@ func TestShuffleShardExpectedInstancesPerZone(t *testing.T) {
 			numZones:  3,
 			expected:  2,
 		},
+		{
+			shardSize: math.MaxInt,
+			numZones:  3,
+			expected:  math.MaxInt,
+		},
 	}
 
 	for _, test := range tests {