Chunk taskArns into groups of 100

provider/ecs.go

@@ -206,13 +206,28 @@ func (provider *ECS) listInstances(ctx context.Context, client *awsClient) ([]ec
 		taskArns = append(taskArns, req.Data.(*ecs.ListTasksOutput).TaskArns...)
 	}
 
-	req, taskResp := client.ecs.DescribeTasksRequest(&ecs.DescribeTasksInput{
-		Tasks:   taskArns,
-		Cluster: &provider.Cluster,
-	})
+	// Early return: if we can't list tasks we have nothing to
+	// describe below - likely empty cluster/permissions are bad.  This
+	// stops the AWS API from returning a 401 when you DescribeTasks
+	// with no input.
+	if len(taskArns) == 0 {
+		return []ecsInstance{}, nil
+	}
+
+	chunkedTaskArns := provider.chunkedTaskArns(taskArns)
+	var tasks []*ecs.Task
+
+	for _, arns := range chunkedTaskArns {
+		req, taskResp := client.ecs.DescribeTasksRequest(&ecs.DescribeTasksInput{
+			Tasks:   arns,
+			Cluster: &provider.Cluster,
+		})
+
+		if err := wrapAws(ctx, req); err != nil {
+			return nil, err
+		}
+		tasks = append(tasks, taskResp.Tasks...)
 
-	if err := wrapAws(ctx, req); err != nil {
-		return nil, err
 	}
 
 	containerInstanceArns := make([]*string, 0)
@@ -221,7 +236,7 @@ func (provider *ECS) listInstances(ctx context.Context, client *awsClient) ([]ec
 	taskDefinitionArns := make([]*string, 0)
 	byTaskDefinition := make(map[string]int)
 
-	for _, task := range taskResp.Tasks {
+	for _, task := range tasks {
 		if _, found := byContainerInstance[*task.ContainerInstanceArn]; !found {
 			byContainerInstance[*task.ContainerInstanceArn] = len(containerInstanceArns)
 			containerInstanceArns = append(containerInstanceArns, task.ContainerInstanceArn)
@@ -243,7 +258,7 @@ func (provider *ECS) listInstances(ctx context.Context, client *awsClient) ([]ec
 	}
 
 	var instances []ecsInstance
-	for _, task := range taskResp.Tasks {
+	for _, task := range tasks {
 
 		machineIdx := byContainerInstance[*task.ContainerInstanceArn]
 		taskDefIdx := byTaskDefinition[*task.TaskDefinitionArn]
@@ -398,6 +413,22 @@ func (provider *ECS) getFrontendRule(i ecsInstance) string {
 	return "Host:" + strings.ToLower(strings.Replace(i.Name, "_", "-", -1)) + "." + provider.Domain
 }
 
+// ECS expects no more than 100 parameters be passed to a DescribeTask call; thus, pack
+// each string into an array capped at 100 elements
+func (provider *ECS) chunkedTaskArns(tasks []*string) [][]*string {
+	var chunkedTasks [][]*string
+	for i := 0; i < len(tasks); i += 100 {
+		sliceEnd := -1
+		if i+100 < len(tasks) {
+			sliceEnd = i + 100
+		} else {
+			sliceEnd = len(tasks)
+		}
+		chunkedTasks = append(chunkedTasks, tasks[i:sliceEnd])
+	}
+	return chunkedTasks
+}
+
 func (i ecsInstance) Protocol() string {
 	if label := i.label("traefik.protocol"); label != "" {
 		return label

provider/ecs_test.go

@@ -308,3 +308,42 @@ func TestFilterInstance(t *testing.T) {
 		}
 	}
 }
+
+func TestTaskChunking(t *testing.T) {
+	provider := &ECS{}
+
+	testval := "a"
+	cases := []struct {
+		count           int
+		expectedLengths []int
+	}{
+		{0, []int(nil)},
+		{1, []int{1}},
+		{99, []int{99}},
+		{100, []int{100}},
+		{101, []int{100, 1}},
+		{199, []int{100, 99}},
+		{200, []int{100, 100}},
+		{201, []int{100, 100, 1}},
+		{555, []int{100, 100, 100, 100, 100, 55}},
+		{1001, []int{100, 100, 100, 100, 100, 100, 100, 100, 100, 100, 1}},
+	}
+
+	for _, c := range cases {
+		var tasks []*string
+		for v := 0; v < c.count; v++ {
+			tasks = append(tasks, &testval)
+		}
+
+		out := provider.chunkedTaskArns(tasks)
+		var outCount []int
+
+		for _, el := range out {
+			outCount = append(outCount, len(el))
+		}
+
+		if !reflect.DeepEqual(outCount, c.expectedLengths) {
+			t.Errorf("Chunking %d elements, expected %#v, got %#v", c.count, c.expectedLengths, outCount)
+		}
+	}
+}