[aws detector] Remove error when instance metadata is unavailable

> Note the failure to detect any resource information MUST NOT be
>  considered an error

When instance metadata is not available, this should not be treated
 as an error.

Small refactoring required to allow tests to mock the client, which
 should be _mostly_ non-impacting for consumers.

CHANGELOG.md

@@ -8,6 +8,10 @@ This project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.htm
 
 ## [Unreleased]
 
+## Fixed
+
+- `/detectors/aws` no longer fails if instance metadata is not available (e.g. not running in AWS) (#401)
+
 ## [0.13.0] - 2020-10-09
 
 ## Added

detectors/aws/aws.go

@@ -16,7 +16,6 @@ package aws
 
 import (
 	"context"
-	"errors"
 
 	"github.com/aws/aws-sdk-go/aws/ec2metadata"
 	"github.com/aws/aws-sdk-go/aws/session"
@@ -27,21 +26,27 @@ import (
 )
 
 // AWS collects resource information of AWS computing instances
-type AWS struct{}
+type AWS struct {
+	c client
+}
+
+type client interface {
+	Available() bool
+	GetInstanceIdentityDocument() (ec2metadata.EC2InstanceIdentityDocument, error)
+}
 
 // compile time assertion that AWS implements the resource.Detector interface.
 var _ resource.Detector = (*AWS)(nil)
 
 // Detect detects associated resources when running in AWS environment.
 func (aws *AWS) Detect(ctx context.Context) (*resource.Resource, error) {
-	session, err := session.NewSession()
+	client, err := aws.client()
 	if err != nil {
 		return nil, err
 	}
 
-	client := ec2metadata.New(session)
 	if !client.Available() {
-		return nil, errors.New("unavailable EC2 client")
+		return nil, nil
 	}
 
 	doc, err := client.GetInstanceIdentityDocument()
@@ -58,3 +63,16 @@ func (aws *AWS) Detect(ctx context.Context) (*resource.Resource, error) {
 
 	return resource.New(labels...), nil
 }
+
+func (aws *AWS) client() (client, error) {
+	if aws.c != nil {
+		return aws.c, nil
+	}
+
+	s, err := session.NewSession()
+	if err != nil {
+		return nil, err
+	}
+
+	return ec2metadata.New(s), nil
+}

detectors/aws/aws_test.go

@@ -0,0 +1,118 @@
+// Copyright The OpenTelemetry Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package aws
+
+import (
+	"context"
+	"errors"
+	"testing"
+	"time"
+
+	"github.com/aws/aws-sdk-go/aws/ec2metadata"
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+
+	"go.opentelemetry.io/otel/sdk/resource"
+	"go.opentelemetry.io/otel/semconv"
+)
+
+func TestAWS_Detect(t *testing.T) {
+	type fields struct {
+		Client client
+	}
+
+	type want struct {
+		Error    string
+		Resource *resource.Resource
+	}
+
+	testTable := map[string]struct {
+		Fields fields
+		Want   want
+	}{
+		"Unavailable": {
+			Fields: fields{Client: &clientMock{}},
+		},
+		"Instance ID Error": {
+			Fields: fields{
+				Client: &clientMock{available: true, idDoc: func() (ec2metadata.EC2InstanceIdentityDocument, error) {
+					return ec2metadata.EC2InstanceIdentityDocument{}, errors.New("id not available")
+				}},
+			},
+			Want: want{Error: "id not available"},
+		},
+		"Instance ID Available": {
+			Fields: fields{
+				Client: &clientMock{available: true, idDoc: func() (ec2metadata.EC2InstanceIdentityDocument, error) {
+					// Example from https://docs.aws.amazon.com/AWSEC2/latest/UserGuide/instance-identity-documents.html
+					doc := ec2metadata.EC2InstanceIdentityDocument{
+						MarketplaceProductCodes: []string{"1abc2defghijklm3nopqrs4tu"},
+						AvailabilityZone:        "us-west-2b",
+						PrivateIP:               "10.158.112.84",
+						Version:                 "2017-09-30",
+						Region:                  "us-west-2",
+						InstanceID:              "i-1234567890abcdef0",
+						InstanceType:            "t2.micro",
+						AccountID:               "123456789012",
+						PendingTime:             time.Date(2016, time.November, 19, 16, 32, 11, 0, time.UTC),
+						ImageID:                 "ami-5fb8c835",
+						Architecture:            "x86_64",
+					}
+
+					return doc, nil
+				}},
+			},
+			Want: want{Resource: resource.New(
+				semconv.CloudProviderAWS,
+				semconv.CloudRegionKey.String("us-west-2"),
+				semconv.CloudAccountIDKey.String("123456789012"),
+				semconv.HostIDKey.String("i-1234567890abcdef0"),
+			)},
+		},
+	}
+
+	for name, tt := range testTable {
+		tt := tt
+
+		t.Run(name, func(t *testing.T) {
+			t.Parallel()
+
+			aws := AWS{c: tt.Fields.Client}
+
+			r, err := aws.Detect(context.Background())
+
+			if tt.Want.Error != "" {
+				require.EqualError(t, err, tt.Want.Error, "Error")
+				return
+			}
+
+			require.NoError(t, err, "Error")
+			assert.Equal(t, tt.Want.Resource, r, "Resource")
+		})
+	}
+}
+
+type clientMock struct {
+	available bool
+	idDoc     func() (ec2metadata.EC2InstanceIdentityDocument, error)
+}
+
+func (c *clientMock) Available() bool {
+	return c.available
+}
+
+func (c *clientMock) GetInstanceIdentityDocument() (ec2metadata.EC2InstanceIdentityDocument, error) {
+	return c.idDoc()
+}

detectors/aws/go.mod

@@ -4,6 +4,7 @@ go 1.14
 
 require (
 	github.com/aws/aws-sdk-go v1.35.7
+	github.com/stretchr/testify v1.6.1
 	go.opentelemetry.io/otel v0.13.0
 	go.opentelemetry.io/otel/sdk v0.13.0
 )