Read real config for the AWS region

This change uses the machinery added to pulumi/lumi#117 to read the
live AWS region config state, and prefer it to `AWS_REGION`.  We
still respect the region environment variable -- since this is the
common way to do configuration like this with AWS tools -- but this
at least avoids the issue of AWS_REGION being different and having
your Lumi scripts compute differing regions and failing impressively.

lib/aws/provider/awsctx/context.go

@@ -18,6 +18,7 @@ package awsctx
 import (
 	"context"
 
+	"github.com/aws/aws-sdk-go/aws"
 	"github.com/aws/aws-sdk-go/aws/session"
 	"github.com/aws/aws-sdk-go/service/apigateway"
 	"github.com/aws/aws-sdk-go/service/dynamodb"
@@ -27,6 +28,8 @@ import (
 	"github.com/aws/aws-sdk-go/service/lambda"
 	"github.com/aws/aws-sdk-go/service/s3"
 	"github.com/golang/glog"
+	"github.com/pkg/errors"
+	"github.com/pulumi/lumi/pkg/resource/provider"
 	"github.com/pulumi/lumi/pkg/util/contract"
 
 	"github.com/pulumi/lumi/lib/aws/provider/arn"
@@ -50,13 +53,25 @@ type Context struct {
 	s3               *s3.S3
 }
 
-func New() (*Context, error) {
+const regionConfig = "aws:config:region"
+
+func New(host *provider.HostClient) (*Context, error) {
 	// Create an AWS session; note that this is safe to share among many operations.
 	glog.V(5).Infof("Creating a new AWS session object w/ default credentials")
 	// IDEA: consider verifying credentials, region, etc. here.
 	// IDEA: currently we just inherit the standard AWS SDK credentials logic; eventually we will want more
 	//     flexibility, I assume, including possibly reading from configuration dynamically.
-	sess, err := session.NewSession()
+	var config []*aws.Config
+	reg, err := host.ReadLocation(regionConfig)
+	if err != nil {
+		return nil, err
+	} else if !reg.IsNull() {
+		if !reg.IsString() {
+			return nil, errors.Errorf("Expected a string for AWS region config '%v'; got %v", regionConfig, reg)
+		}
+		config = append(config, &aws.Config{Region: aws.String(reg.StringValue())})
+	}
+	sess, err := session.NewSession(config...)
 	if err != nil {
 		return nil, err
 	}

lib/aws/provider/main.go

@@ -16,40 +16,16 @@
 package main
 
 import (
-	"fmt"
-	"os"
-
+	"github.com/pulumi/lumi/pkg/resource/provider"
 	"github.com/pulumi/lumi/pkg/util/cmdutil"
-	"github.com/pulumi/lumi/pkg/util/rpcutil"
 	"github.com/pulumi/lumi/sdk/go/pkg/lumirpc"
-	"google.golang.org/grpc"
 )
 
 func main() {
-	// Initialize loggers before going any further.
-	cmdutil.InitLogging(false, 0, false)
-
-	// Fire up a gRPC server, letting the kernel choose a free port for us.
-	port, done, err := rpcutil.Serve(0, nil, []func(*grpc.Server) error{
-		func(srv *grpc.Server) error {
-			prov, err := NewProvider()
-			if err != nil {
-				return fmt.Errorf("failed to create AWS resource provider: %v", err)
-			}
-			lumirpc.RegisterResourceProviderServer(srv, prov)
-			return nil
-		},
-	})
-	if err != nil {
-		fmt.Fprintf(os.Stderr, "fatal: %v\n", err)
-		os.Exit(-1)
-	}
-
-	// The resource provider protocol requires that we now write out the port we have chosen to listen on.
-	fmt.Printf("%d\n", port)
-
-	// Finally, wait for the server to stop serving.
-	if err := <-done; err != nil {
-		fmt.Fprintf(os.Stderr, "fatal: %v\n", err)
+	// Create a new resurce provider server and listen for and serve incoming connections.
+	if err := provider.Main(func(host *provider.HostClient) (lumirpc.ResourceProviderServer, error) {
+		return NewProvider(host)
+	}); err != nil {
+		cmdutil.ExitError(err.Error())
 	}
 }

lib/aws/provider/provider.go

@@ -19,6 +19,7 @@ import (
 	"fmt"
 
 	pbempty "github.com/golang/protobuf/ptypes/empty"
+	"github.com/pulumi/lumi/pkg/resource/provider"
 	"github.com/pulumi/lumi/pkg/tokens"
 	"github.com/pulumi/lumi/sdk/go/pkg/lumirpc"
 	"golang.org/x/net/context"
@@ -39,8 +40,8 @@ type Provider struct {
 }
 
 // NewProvider creates a new provider instance with server objects registered for every resource type.
-func NewProvider() (*Provider, error) {
-	ctx, err := awsctx.New()
+func NewProvider(host *provider.HostClient) (*Provider, error) {
+	ctx, err := awsctx.New(host)
 	if err != nil {
 		return nil, err
 	}