fingerprint: handle incomplete AWS immitation APIs

Fix a regression where we accidentally started treating non-AWS
environments as AWS environments, resulting in bad networking settings.

Two factors some at play:

First, in [1], we accidentally switched the ultimate AWS test from
checking `ami-id` to `instance-id`.  This means that nomad started
treating more environments as AWS; e.g. Hetzner implements `instance-id`
but not `ami-id`.

Second, some of these environments return empty values instead of
errors!  Hetzner returns empty 200 response for `local-ipv4`, resulting
into bad networking configuration.

This change fix the situation by restoring the check to `ami-id` and
ensuring that we only set network configuration when the ip address is
not-empty.  Also, be more defensive around response whitespace input.

[1] #6779

client/fingerprint/env_aws.go

@@ -80,15 +80,10 @@ func (f *EnvAWSFingerprint) Fingerprint(request *FingerprintRequest, response *F
 		return fmt.Errorf("failed to setup ec2Metadata client: %v", err)
 	}
 
-	if !ec2meta.Available() {
+	if !isAWS(ec2meta) {
 		return nil
 	}
 
-	// newNetwork is populated and added to the Nodes resources
-	newNetwork := &structs.NetworkResource{
-		Device: "eth0",
-	}
-
 	// Keys and whether they should be namespaced as unique. Any key whose value
 	// uniquely identifies a node, such as ip, should be marked as unique. When
 	// marked as unique, the key isn't included in the computed node class.
@@ -103,9 +98,14 @@ func (f *EnvAWSFingerprint) Fingerprint(request *FingerprintRequest, response *F
 		"public-ipv4":                 true,
 		"placement/availability-zone": false,
 	}
+
 	for k, unique := range keys {
 		resp, err := ec2meta.GetMetadata(k)
-		if awsErr, ok := err.(awserr.RequestFailure); ok {
+		v := strings.TrimSpace(strings.Trim(resp, "\n"))
+		if v == "" {
+			f.logger.Debug("read an empty value", "attribute", k)
+			continue
+		} else if awsErr, ok := err.(awserr.RequestFailure); ok {
 			f.logger.Debug("could not read attribute value", "attribute", k, "error", awsErr)
 			continue
 		} else if awsErr, ok := err.(awserr.Error); ok {
@@ -125,45 +125,28 @@ func (f *EnvAWSFingerprint) Fingerprint(request *FingerprintRequest, response *F
 			key = structs.UniqueNamespace(key)
 		}
 
-		response.AddAttribute(key, strings.Trim(resp, "\n"))
+		response.AddAttribute(key, v)
 	}
 
+	// newNetwork is populated and added to the Nodes resources
+	var newNetwork *structs.NetworkResource
+
 	// copy over network specific information
 	if val, ok := response.Attributes["unique.platform.aws.local-ipv4"]; ok && val != "" {
 		response.AddAttribute("unique.network.ip-address", val)
-		newNetwork.IP = val
-		newNetwork.CIDR = newNetwork.IP + "/32"
-	}
 
-	// find LinkSpeed from lookup
-	throughput := cfg.NetworkSpeed
-	if throughput == 0 {
-		throughput = f.linkSpeed(ec2meta)
-	}
-	if throughput == 0 {
-		// Failed to determine speed. Check if the network fingerprint got it
-		found := false
-		if request.Node.Resources != nil && len(request.Node.Resources.Networks) > 0 {
-			for _, n := range request.Node.Resources.Networks {
-				if n.IP == newNetwork.IP {
-					throughput = n.MBits
-					found = true
-					break
-				}
-			}
+		newNetwork = &structs.NetworkResource{
+			Device: "eth0",
+			IP:     val,
+			CIDR:   val + "/32",
+			MBits:  f.throughput(request, ec2meta, val),
 		}
 
-		// Nothing detected so default
-		if !found {
-			throughput = defaultNetworkSpeed
+		response.NodeResources = &structs.NodeResources{
+			Networks: []*structs.NetworkResource{newNetwork},
 		}
 	}
 
-	newNetwork.MBits = throughput
-	response.NodeResources = &structs.NodeResources{
-		Networks: []*structs.NetworkResource{newNetwork},
-	}
-
 	// populate Links
 	response.AddLink("aws.ec2", fmt.Sprintf("%s.%s",
 		response.Attributes["platform.aws.placement.availability-zone"],
@@ -173,6 +156,28 @@ func (f *EnvAWSFingerprint) Fingerprint(request *FingerprintRequest, response *F
 	return nil
 }
 
+func (f *EnvAWSFingerprint) throughput(request *FingerprintRequest, ec2meta *ec2metadata.EC2Metadata, ip string) int {
+	throughput := request.Config.NetworkSpeed
+	if throughput != 0 {
+		return throughput
+	}
+
+	throughput = f.linkSpeed(ec2meta)
+	if throughput != 0 {
+		return throughput
+	}
+
+	if request.Node.Resources != nil && len(request.Node.Resources.Networks) > 0 {
+		for _, n := range request.Node.Resources.Networks {
+			if n.IP == ip {
+				return n.MBits
+			}
+		}
+	}
+
+	return defaultNetworkSpeed
+}
+
 // EnvAWSFingerprint uses lookup table to approximate network speeds
 func (f *EnvAWSFingerprint) linkSpeed(ec2meta *ec2metadata.EC2Metadata) int {
 
@@ -211,3 +216,8 @@ func ec2MetaClient(endpoint string, timeout time.Duration) (*ec2metadata.EC2Meta
 	}
 	return ec2metadata.New(session, c), nil
 }
+
+func isAWS(ec2meta *ec2metadata.EC2Metadata) bool {
+	v, err := ec2meta.GetMetadata("ami-id")
+	return err == nil && v != ""
+}