Initial Functionality

The initial functionality works.  There's still a number of TODOs to
clean up, and some edge cases to work around, and some errors that could
be handled better.

cmd/app/start.go

@@ -0,0 +1,147 @@
+/*
+Copyright 2017 The Kubernetes 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 app
+
+import (
+	"net/http"
+	"net/url"
+	"fmt"
+	"io"
+	"time"
+
+	"github.com/spf13/cobra"
+	"k8s.io/client-go/rest"
+	"k8s.io/client-go/pkg/api"
+	"k8s.io/client-go/tools/clientcmd"
+	"k8s.io/client-go/dynamic"
+	"k8s.io/client-go/discovery"
+
+	"k8s.io/custom-metrics-boilerplate/pkg/cmd/server"
+	cmprov "github.com/directxman12/k8s-prometheus-adapter/pkg/custom-provider"
+	prom "github.com/directxman12/k8s-prometheus-adapter/pkg/client"
+)
+
+// NewCommandStartPrometheusAdapterServer provides a CLI handler for 'start master' command
+func NewCommandStartPrometheusAdapterServer(out, errOut io.Writer, stopCh <-chan struct{}) *cobra.Command {
+	baseOpts := server.NewCustomMetricsAdapterServerOptions(out, errOut)
+	o := PrometheusAdapterServerOptions{
+		CustomMetricsAdapterServerOptions: baseOpts,
+		MetricsRelistInterval: 10 * time.Minute,
+		RateInterval: 5 * time.Minute,
+		PrometheusURL: "https://localhost",
+	}
+
+	cmd := &cobra.Command{
+		Short: "Launch the custom metrics API adapter server",
+		Long:  "Launch the custom metrics API adapter server",
+		RunE: func(c *cobra.Command, args []string) error {
+			if err := o.Complete(); err != nil {
+				return err
+			}
+			if err := o.Validate(args); err != nil {
+				return err
+			}
+			if err := o.RunCustomMetricsAdapterServer(stopCh); err != nil {
+				return err
+			}
+			return nil
+		},
+	}
+
+	flags := cmd.Flags()
+	o.SecureServing.AddFlags(flags)
+	o.Authentication.AddFlags(flags)
+	o.Authorization.AddFlags(flags)
+	o.Features.AddFlags(flags)
+
+	flags.StringVar(&o.RemoteKubeConfigFile, "lister-kubeconfig", o.RemoteKubeConfigFile, ""+
+		"kubeconfig file pointing at the 'core' kubernetes server with enough rights to list "+
+		"any described objets")
+	flags.DurationVar(&o.MetricsRelistInterval, "metrics-relist-interval", o.MetricsRelistInterval, ""+
+		"interval at which to re-list the set of all available metrics from Prometheus")
+	flags.DurationVar(&o.RateInterval, "rate-interval", o.RateInterval, ""+
+		"period of time used to calculate rate metrics from cumulative metrics")
+	flags.StringVar(&o.PrometheusURL, "prometheus-url", o.PrometheusURL,
+		"URL and configuration for connecting to Prometheus.  Query parameters are used to configure the connection")
+
+	return cmd
+}
+
+func (o PrometheusAdapterServerOptions) RunCustomMetricsAdapterServer(stopCh <-chan struct{}) error {
+	config, err := o.Config()
+	if err != nil {
+		return err
+	}
+
+	var clientConfig *rest.Config
+	if len(o.RemoteKubeConfigFile) > 0 {
+		loadingRules := &clientcmd.ClientConfigLoadingRules{ExplicitPath: o.RemoteKubeConfigFile}
+		loader := clientcmd.NewNonInteractiveDeferredLoadingClientConfig(loadingRules, &clientcmd.ConfigOverrides{})
+
+		clientConfig, err = loader.ClientConfig()
+	} else {
+		clientConfig, err = rest.InClusterConfig()
+	}
+	if err != nil {
+		return fmt.Errorf("unable to construct lister client config to initialize provider: %v", err)
+	}
+
+	discoveryClient, err := discovery.NewDiscoveryClientForConfig(clientConfig)
+	if err != nil {
+		return fmt.Errorf("unable to construct discovery client for dynamic client: %v", err)
+	}
+
+	// TODO: this needs to refresh it's discovery info every once and a while
+	resources, err := discovery.GetAPIGroupResources(discoveryClient)
+	if err != nil {
+		return fmt.Errorf("unable to construct discovery REST mapper: unable to fetch list of resources: %v", err)
+	}
+	dynamicMapper := discovery.NewRESTMapper(resources, api.Registry.InterfacesFor)
+
+	clientPool := dynamic.NewClientPool(clientConfig, dynamicMapper, dynamic.LegacyAPIPathResolverFunc)
+	if err != nil {
+		return fmt.Errorf("unable to construct lister client to initialize provider: %v", err)
+	}
+
+	// TODO: actually configure this client (strip query vars, etc)
+	baseURL, err := url.Parse(o.PrometheusURL)
+	if err != nil {
+		return fmt.Errorf("invalid Prometheus URL %q: %v", baseURL, err)
+	}
+	promClient := prom.NewClient(http.DefaultClient, baseURL)
+
+	cmProvider := cmprov.NewPrometheusProvider(dynamicMapper, clientPool, promClient, o.MetricsRelistInterval, o.RateInterval)
+
+	server, err := config.Complete().New(cmProvider)
+	if err != nil {
+		return err
+	}
+	return server.GenericAPIServer.PrepareRun().Run(stopCh)
+}
+
+type PrometheusAdapterServerOptions struct {
+	*server.CustomMetricsAdapterServerOptions
+
+	// RemoteKubeConfigFile is the config used to list pods from the master API server
+	RemoteKubeConfigFile string
+	// MetricsRelistInterval is the interval at which to relist the set of available metrics
+	MetricsRelistInterval time.Duration
+	// RateInterval is the period of time used to calculate rate metrics
+	RateInterval time.Duration
+	// PrometheusURL is the URL describing how to connect to Prometheus.  Query parameters configure connection options.
+	PrometheusURL string
+}