add api url setting and add it as one of the template fields we optio…

…nally append to the metadata document. (#66)

cmd/serve.go

@@ -90,6 +90,9 @@ func init() {
 	serveCmd.Flags().StringSlice("gin-trusted-proxies", []string{}, "Comma-separated list of IP addresses, like `\"192.168.1.1,10.0.0.1\"`. When running the Metadata Service behind something like a reverse proxy or load balancer, you may need to set this so that gin's `(*Context).ClientIP()` method returns a value provided by the proxy in a header like `X-Forwarded-For`.")
 	viperBindFlag("gin.trustedproxies", serveCmd.Flags().Lookup("gin-trusted-proxies"))
 
+	serveCmd.Flags().String("api-url", "", "An optional golang template string used to build a URL which instances can use as a reference to the Metadata Service API itself. This template string will be evaluated against the instance metadata, and appended as an 'api_url' field on the metadata document served to instances. If no template string is specified, the 'api_url' field will not be added to the metadata document.")
+	viperBindFlag("metadata.api_url", serveCmd.Flags().Lookup("api-url"))
+
 	serveCmd.Flags().String("phone-home-url", "", "An optional golang template string used to build a URL which instances can use as part of a 'phone home' process. This template string will be evaluated against the instance metadata, and appended as a 'phone_home_url' field on the metadata document served to instances. If no template string is specified, the 'phone_home_url' field will not be added to the metadata document.")
 	viperBindFlag("metadata.phone_home_url", serveCmd.Flags().Lookup("phone-home-url"))
 
@@ -180,9 +183,19 @@ func getLookupClient(ctx context.Context) (*lookup.ServiceClient, error) {
 func getTemplateFields() map[string]template.Template {
 	templates := make(map[string]template.Template)
 
+	apiURL := viper.GetString("metadata.api_url")
 	phoneHomeURL := viper.GetString("metadata.phone_home_url")
 	userStateURL := viper.GetString("metadata.user_state_url")
 
+	if len(apiURL) > 0 {
+		apiURLTempl, err := template.New("apiURL").Parse(apiURL)
+		if err != nil {
+			logger.Fatalf("failed to parse API URL template (%s)", apiURL, "error", err)
+		}
+
+		templates["api_url"] = *apiURLTempl
+	}
+
 	if len(phoneHomeURL) > 0 {
 		phoneHomeTempl, err := template.New("phoneHomeURL").Parse(phoneHomeURL)
 		if err != nil {

pkg/api/v1/router_instance_metadata_test.go

@@ -116,6 +116,11 @@ func TestGetMetadataByIP(t *testing.T) {
 }
 
 func TestGetMetadataByIPWithTemplateFields(t *testing.T) {
+	apiURLTmpl, err := template.New("apiURL").Parse("https://metadata-service")
+	if err != nil {
+		t.Error(err)
+	}
+
 	phoneHomeTmpl, err := template.New("phoneHomeURL").Parse("https://{{.facility}}.phone.home/phone-home")
 	if err != nil {
 		t.Error(err)
@@ -145,6 +150,7 @@ func TestGetMetadataByIPWithTemplateFields(t *testing.T) {
 
 	config := TestServerConfig{
 		TemplateFields: map[string]template.Template{
+			"api_url":        *apiURLTmpl,
 			"phone_home_url": *phoneHomeTmpl,
 			"user_state_url": *userStateTmpl,
 			"missing_field":  *missingFieldTmpl,
@@ -171,6 +177,7 @@ func TestGetMetadataByIPWithTemplateFields(t *testing.T) {
 		t.Fatal(err)
 	}
 
+	assert.Equal(t, "https://metadata-service", resultMap["api_url"])
 	assert.Equal(t, "https://da11.phone.home/phone-home", resultMap["phone_home_url"])
 	assert.Equal(t, fmt.Sprintf("https://da.user.state/events/%s", dbtools.FixtureInstanceA.InstanceID), resultMap["user_state_url"])
 	assert.Equal(t, "instance-a", resultMap["hostname"])