Add supports for stats in ACI provider

This adds a new, optional, interface for providers that want to provide
stats.

providers/azure/client/aci/metrics.go

@@ -0,0 +1,97 @@
+package aci
+
+import (
+	"context"
+	"encoding/json"
+	"net/http"
+	"net/url"
+	"path"
+	"time"
+
+	"github.com/pkg/errors"
+	"github.com/virtual-kubelet/virtual-kubelet/providers/azure/client/api"
+)
+
+// GetContainerGroupMetrics gets metrics for the provided container group
+func (c *Client) GetContainerGroupMetrics(ctx context.Context, resourceGroup, containerGroup string, options MetricsRequest) (*ContainerGroupMetricsResult, error) {
+	if len(options.Types) == 0 {
+		return nil, errors.New("must provide metrics types to fetch")
+	}
+	if options.Start.After(options.End) || options.Start.Equal(options.End) && !options.Start.IsZero() {
+		return nil, errors.Errorf("end parameter must be after start: start=%s, end=%s", options.Start, options.End)
+	}
+
+	var metricNames string
+	for _, t := range options.Types {
+		if len(metricNames) > 0 {
+			metricNames += ","
+		}
+		metricNames += string(t)
+	}
+
+	var ag string
+	for _, a := range options.Aggregations {
+		if len(ag) > 0 {
+			ag += ","
+		}
+		ag += string(a)
+	}
+
+	urlParams := url.Values{
+		"api-version": []string{"2018-01-01"},
+		"aggregation": []string{ag},
+		"metricnames": []string{metricNames},
+		"interval":    []string{"PT1M"}, // TODO: make configurable?
+	}
+
+	if options.Dimension != "" {
+		urlParams.Add("$filter", options.Dimension)
+	}
+
+	if !options.Start.IsZero() || !options.End.IsZero() {
+		urlParams.Add("timespan", path.Join(options.Start.Format(time.RFC3339), options.End.Format(time.RFC3339)))
+	}
+
+	// Create the url.
+	uri := api.ResolveRelative(c.auth.ResourceManagerEndpoint, containerGroupMetricsURLPath)
+	uri += "?" + url.Values(urlParams).Encode()
+
+	// Create the request.
+	req, err := http.NewRequest("GET", uri, nil)
+	if err != nil {
+		return nil, errors.Wrap(err, "creating get container group metrics uri request failed")
+	}
+	req = req.WithContext(ctx)
+
+	// Add the parameters to the url.
+	if err := api.ExpandURL(req.URL, map[string]string{
+		"subscriptionId":     c.auth.SubscriptionID,
+		"resourceGroup":      resourceGroup,
+		"containerGroupName": containerGroup,
+	}); err != nil {
+		return nil, errors.Wrap(err, "expanding URL with parameters failed")
+	}
+
+	// SEnd the request.
+	resp, err := c.hc.Do(req)
+	if err != nil {
+		return nil, errors.Wrap(err, "sending get container group metrics request failed")
+	}
+	defer resp.Body.Close()
+
+	// 200 (OK) is a success response.
+	if err := api.CheckResponse(resp); err != nil {
+		return nil, err
+	}
+
+	// Decode the body from the response.
+	if resp.Body == nil {
+		return nil, errors.New("container group metrics returned an empty body in the response")
+	}
+	var metrics ContainerGroupMetricsResult
+	if err := json.NewDecoder(resp.Body).Decode(&metrics); err != nil {
+		return nil, errors.Wrap(err, "decoding get container group metrics response body failed")
+	}
+
+	return &metrics, nil
+}