Refactor Azure IMDS client and metadata

internal/cloud/azure/imds.go

@@ -3,8 +3,10 @@ package azure
 import (
 	"context"
 	"encoding/json"
+	"errors"
 	"io"
 	"net/http"
+	"time"
 )
 
 // subset of azure imds API: https://docs.microsoft.com/en-us/azure/virtual-machines/windows/instance-metadata-service?tabs=linux
@@ -13,17 +15,95 @@ import (
 const (
 	imdsURL        = "http://169.254.169.254/metadata/instance"
 	imdsAPIVersion = "2021-02-01"
+	maxCacheAge    = 12 * time.Hour
 )
 
 type imdsClient struct {
 	client *http.Client
+
+	cache     metadataResponse
+	cacheTime time.Time
 }
 
-// Retrieve retrieves instance metadata from the azure imds API.
-func (c *imdsClient) Retrieve(ctx context.Context) (metadataResponse, error) {
-	req, err := http.NewRequestWithContext(ctx, "GET", imdsURL, http.NoBody)
+// ProviderID returns the provider ID of the instance the function is called from.
+func (c *imdsClient) ProviderID(ctx context.Context) (string, error) {
+	if c.timeForUpdate() || c.cache.Compute.ResourceID == "" {
+		if err := c.update(ctx); err != nil {
+			return "", err
+		}
+	}
+
+	if c.cache.Compute.ResourceID == "" {
+		return "", errors.New("unable to get provider id")
+	}
+
+	return c.cache.Compute.ResourceID, nil
+}
+
+// SubscriptionID returns the subscription ID of the instance the function
+// is called from.
+func (c *imdsClient) SubscriptionID(ctx context.Context) (string, error) {
+	if c.timeForUpdate() || c.cache.Compute.SubscriptionID == "" {
+		if err := c.update(ctx); err != nil {
+			return "", err
+		}
+	}
+
+	if c.cache.Compute.SubscriptionID == "" {
+		return "", errors.New("unable to get subscription id")
+	}
+
+	return c.cache.Compute.SubscriptionID, nil
+}
+
+// ResourceGroup returns the resource group of the instance the function
+// is called from.
+func (c *imdsClient) ResourceGroup(ctx context.Context) (string, error) {
+	if c.timeForUpdate() || c.cache.Compute.ResourceGroup == "" {
+		if err := c.update(ctx); err != nil {
+			return "", err
+		}
+	}
+
+	if c.cache.Compute.ResourceGroup == "" {
+		return "", errors.New("unable to get resource group")
+	}
+
+	return c.cache.Compute.ResourceGroup, nil
+}
+
+// UID returns the UID of the cluster, based on the tags on the instance
+// the function is calles from, which are inherited from the scale set.
+func (c *imdsClient) UID(ctx context.Context) (string, error) {
+	if c.timeForUpdate() || len(c.cache.Compute.Tags) == 0 {
+		if err := c.update(ctx); err != nil {
+			return "", err
+		}
+	}
+
+	if len(c.cache.Compute.Tags) == 0 {
+		return "", errors.New("unable to get uid")
+	}
+
+	for _, tag := range c.cache.Compute.Tags {
+		if tag.Name == "uid" {
+			return tag.Value, nil
+		}
+	}
+
+	return "", errors.New("unable to get uid from metadata tags")
+}
+
+// timeForUpdate checks whether an update is needed due to cache age.
+func (c *imdsClient) timeForUpdate() bool {
+	return time.Since(c.cacheTime) > maxCacheAge
+}
+
+// update updates instance metadata from the azure imds API.
+func (c *imdsClient) update(ctx context.Context) error {
+	req, err := http.NewRequestWithContext(ctx, http.MethodGet, imdsURL, http.NoBody)
 	if err != nil {
-		return metadataResponse{}, err
+		return err
 	}
 	req.Header.Add("Metadata", "True")
 	query := req.URL.Query()
@@ -32,23 +112,36 @@ func (c *imdsClient) Retrieve(ctx context.Context) (metadataResponse, error) {
 	req.URL.RawQuery = query.Encode()
 	resp, err := c.client.Do(req)
 	if err != nil {
-		return metadataResponse{}, err
+		return err
 	}
 	defer resp.Body.Close()
 	body, err := io.ReadAll(resp.Body)
 	if err != nil {
-		return metadataResponse{}, err
+		return err
 	}
 	var res metadataResponse
 	if err := json.Unmarshal(body, &res); err != nil {
-		return metadataResponse{}, err
+		return err
 	}
-	return res, nil
+
+	c.cache = res
+	c.cacheTime = time.Now()
+	return nil
 }
 
 // metadataResponse contains metadataResponse with only the required values.
 type metadataResponse struct {
-	Compute struct {
-		ResourceID string `json:"resourceId,omitempty"`
-	} `json:"compute,omitempty"`
+	Compute metadataResponseCompute `json:"compute,omitempty"`
+}
+
+type metadataResponseCompute struct {
+	ResourceID     string        `json:"resourceId,omitempty"`
+	SubscriptionID string        `json:"subscriptionId,omitempty"`
+	ResourceGroup  string        `json:"resourceGroupName,omitempty"`
+	Tags           []metadataTag `json:"tagsList,omitempty"`
+}
+
+type metadataTag struct {
+	Name  string `json:"name,omitempty"`
+	Value string `json:"value,omitempty"`
 }