A touch more work on GetExternalMetric.

Also added some comments for anyone reviewing this to help explain what I'm thinking.

Gopkg.lock

@@ -68,19 +68,6 @@
   revision = "346938d642f2ec3594ed81d874461961cd0faa76"
   version = "v1.1.0"
 
-[[projects]]
-  branch = "master"
-  name = "github.com/directxman12/k8s-prometheus-adapter"
-  packages = [
-    "cmd/adapter/app",
-    "cmd/config-gen/utils",
-    "pkg/client",
-    "pkg/client/metrics",
-    "pkg/config",
-    "pkg/custom-provider"
-  ]
-  revision = "7b606a79fc2fdc4246e455e8f28503e0b4807a92"
-
 [[projects]]
   name = "github.com/elazarl/go-bindata-assetfs"
   packages = ["."]
@@ -815,6 +802,6 @@
 [solve-meta]
   analyzer-name = "dep"
   analyzer-version = 1
-  inputs-digest = "66b8ba4b829725e88ff6ba39c022bdf9670bdffa53ef9f8094c84e0c1447d2db"
+  inputs-digest = "14918e76a061ac7466e9c6fa723afb8a0c888021c78e6a75c8275d5205e2bb60"
   solver-name = "gps-cdcl"
   solver-version = 1

pkg/custom-provider/external_provider.go

@@ -17,9 +17,12 @@ limitations under the License.
 package provider
 
 import (
+	"context"
 	"fmt"
 	"time"
 
+	pmodel "github.com/prometheus/common/model"
+
 	"github.com/kubernetes-incubator/custom-metrics-apiserver/pkg/provider"
 	apimeta "k8s.io/apimachinery/pkg/api/meta"
 	"k8s.io/apimachinery/pkg/labels"
@@ -29,6 +32,11 @@ import (
 	prom "github.com/directxman12/k8s-prometheus-adapter/pkg/client"
 )
 
+//TODO: Some of these members may not be necessary.
+//Some of them are definitely duplicated between the
+//external and custom providers. They should probably share
+//the same instances of these objects (especially the SeriesRegistry)
+//to cut down on unnecessary chatter/bookkeeping.
 type externalPrometheusProvider struct {
 	mapper       apimeta.RESTMapper
 	kubeClient   dynamic.Interface
@@ -38,6 +46,12 @@ type externalPrometheusProvider struct {
 	SeriesRegistry
 }
 
+//TODO: It probably makes more sense to, once this is functional and complete, roll the
+//customPrometheusProvider and externalPrometheusProvider up into a single type
+//that implements both interfaces or provide a thin wrapper that composes them.
+//Just glancing at start.go looks like it would be much more straightforward
+//to do one of those two things instead of trying to run the two providers
+//independently.
 func NewExternalPrometheusProvider(mapper apimeta.RESTMapper, kubeClient dynamic.Interface, promClient prom.Client, namers []MetricNamer, updateInterval time.Duration, queryBuilder ExternalMetricQueryBuilder) (provider.ExternalMetricsProvider, Runnable) {
 	lister := &cachingMetricsLister{
 		updateInterval: updateInterval,
@@ -59,21 +73,17 @@ func NewExternalPrometheusProvider(mapper apimeta.RESTMapper, kubeClient dynamic
 }
 
 func (p *externalPrometheusProvider) GetExternalMetric(namespace string, metricName string, metricSelector labels.Selector) (*external_metrics.ExternalMetricValueList, error) {
-	//TODO: Steps
-	//1. Generate a Prometheus Query.
-	//   Something like my_metric{namespace="namespace" some_label="some_value"}
-	//2. Send that query to Prometheus.
-	//3. Adapt the results.
-	//The query generation for external metrics is much more straightforward
-	//than for custom metrics because no renaming is applied.
-	//So we'll just start with some simple string operations and see how far that gets us.
-	//Then I'll circle back and figure out how much code reuse I can get out of the original implementation.
 	query := p.queryBuilder.BuildPrometheusQuery(namespace, metricName, metricSelector)
+	selector := prom.Selector(query)
+
+	//TODO: I don't yet know what a context is, but apparently I should use a real one.
+	queryResults, err := p.promClient.Query(context.TODO(), pmodel.Now(), selector)
 
 	//TODO: Only here to stop compiler issues in this incomplete code.
-	fmt.Printf(query)
+	fmt.Printf("%s, %s", queryResults, err)
 
-	//TODO: Construct a real result.
+	//TODO: Check for errors. See what the custromPrometheusProvider does for errors.
+	//TODO: Adapt the results in queryResults to the appropriate return type.
 	return nil, nil
 }