Fix 400 bad request on AWS ECS API

provider/ecs/ecs.go

@@ -347,43 +347,47 @@ func (p *Provider) lookupEc2Instances(ctx context.Context, client *awsClient, cl
 		}
 	}
 
-	resp, err := client.ecs.DescribeContainerInstancesWithContext(ctx, &ecs.DescribeContainerInstancesInput{
+	for _, arns := range p.chunkIDs(containerInstancesArns) {
-		ContainerInstances: containerInstancesArns,
+		resp, err := client.ecs.DescribeContainerInstancesWithContext(ctx, &ecs.DescribeContainerInstancesInput{
-		Cluster:            clusterName,
+			ContainerInstances: arns,
-	})
+			Cluster:            clusterName,
-
-	if err != nil {
-		log.Errorf("Unable to describe container instances: %s", err)
-		return nil, err
-	}
-
-	for _, container := range resp.ContainerInstances {
-		instanceIds[aws.StringValue(container.Ec2InstanceId)] = aws.StringValue(container.ContainerInstanceArn)
-		instanceArns = append(instanceArns, container.Ec2InstanceId)
-	}
-
-	if len(instanceArns) > 0 {
-		input := &ec2.DescribeInstancesInput{
-			InstanceIds: instanceArns,
-		}
-
-		err = client.ec2.DescribeInstancesPagesWithContext(ctx, input, func(page *ec2.DescribeInstancesOutput, lastPage bool) bool {
-			if len(page.Reservations) > 0 {
-				for _, r := range page.Reservations {
-					for _, i := range r.Instances {
-						if i.InstanceId != nil {
-							ec2Instances[instanceIds[aws.StringValue(i.InstanceId)]] = i
-						}
-					}
-				}
-			}
-			return !lastPage
 		})
 
 		if err != nil {
-			log.Errorf("Unable to describe instances: %s", err)
+			log.Errorf("Unable to describe container instances: %v", err)
 			return nil, err
 		}
+
+		for _, container := range resp.ContainerInstances {
+			instanceIds[aws.StringValue(container.Ec2InstanceId)] = aws.StringValue(container.ContainerInstanceArn)
+			instanceArns = append(instanceArns, container.Ec2InstanceId)
+		}
+	}
+
+	if len(instanceArns) > 0 {
+		for _, ids := range p.chunkIDs(instanceArns) {
+			input := &ec2.DescribeInstancesInput{
+				InstanceIds: ids,
+			}
+
+			err := client.ec2.DescribeInstancesPagesWithContext(ctx, input, func(page *ec2.DescribeInstancesOutput, lastPage bool) bool {
+				if len(page.Reservations) > 0 {
+					for _, r := range page.Reservations {
+						for _, i := range r.Instances {
+							if i.InstanceId != nil {
+								ec2Instances[instanceIds[aws.StringValue(i.InstanceId)]] = i
+							}
+						}
+					}
+				}
+				return !lastPage
+			})
+
+			if err != nil {
+				log.Errorf("Unable to describe instances [%s]: %v", err)
+				return nil, err
+			}
+		}
 	}
 
 	return ec2Instances, nil
@@ -414,3 +418,19 @@ func (p *Provider) loadECSConfig(ctx context.Context, client *awsClient) (*types
 
 	return p.buildConfiguration(instances)
 }
+
+// chunkIDs ECS expects no more than 100 parameters be passed to a API call;
+// thus, pack each string into an array capped at 100 elements
+func (p *Provider) chunkIDs(ids []*string) [][]*string {
+	var chuncked [][]*string
+	for i := 0; i < len(ids); i += 100 {
+		sliceEnd := -1
+		if i+100 < len(ids) {
+			sliceEnd = i + 100
+		} else {
+			sliceEnd = len(ids)
+		}
+		chuncked = append(chuncked, ids[i:sliceEnd])
+	}
+	return chuncked
+}

provider/ecs/ecs_test.go

@@ -0,0 +1,88 @@
+package ecs
+
+import (
+	"testing"
+
+	"github.com/aws/aws-sdk-go/aws"
+	"github.com/stretchr/testify/assert"
+)
+
+func TestChunkIDs(t *testing.T) {
+	provider := &Provider{}
+
+	testCases := []struct {
+		desc     string
+		count    int
+		expected []int
+	}{
+		{
+			desc:     "0 element",
+			count:    0,
+			expected: []int(nil),
+		},
+		{
+			desc:     "1 element",
+			count:    1,
+			expected: []int{1},
+		},
+		{
+			desc:     "99 elements, 1 chunk",
+			count:    99,
+			expected: []int{99},
+		},
+		{
+			desc:     "100 elements, 1 chunk",
+			count:    100,
+			expected: []int{100},
+		},
+		{
+			desc:     "101 elements, 2 chunks",
+			count:    101,
+			expected: []int{100, 1},
+		},
+		{
+			desc:     "199 elements, 2 chunks",
+			count:    199,
+			expected: []int{100, 99},
+		},
+		{
+			desc:     "200 elements, 2 chunks",
+			count:    200,
+			expected: []int{100, 100},
+		},
+		{
+			desc:     "201 elements, 3 chunks",
+			count:    201,
+			expected: []int{100, 100, 1},
+		},
+		{
+			desc:     "555 elements, 5 chunks",
+			count:    555,
+			expected: []int{100, 100, 100, 100, 100, 55},
+		},
+		{
+			desc:     "1001 elements, 11 chunks",
+			count:    1001,
+			expected: []int{100, 100, 100, 100, 100, 100, 100, 100, 100, 100, 1},
+		},
+	}
+
+	for _, test := range testCases {
+		test := test
+		t.Run(test.desc, func(t *testing.T) {
+			t.Parallel()
+
+			var IDs []*string
+			for v := 0; v < test.count; v++ {
+				IDs = append(IDs, aws.String("a"))
+			}
+
+			var outCount []int
+			for _, el := range provider.chunkIDs(IDs) {
+				outCount = append(outCount, len(el))
+			}
+
+			assert.Equal(t, test.expected, outCount)
+		})
+	}
+}