Fetch only the required podMetrics for the given component (#17489)

The `PodMetrics` are now limited by `labelSelector` like already done
for pods and probably other requests to Kubernetes.  This limits the
amount of data that is fetched.

Tested locally by modifying `app-config.yaml` and an example component
to use an internal cluster, which leads to the following request size
improvements:

Before: 344.71 kB compressed, 6.89 MB uncompressed
After: 12.01 kB compressed, 238.86 kB uncompressed

For the POST http://localhost:7007/api/kubernetes/services/playback-order
call, in a Kubernetes cluster with ~500 pods.

Fixes #17450.

Signed-off-by: Luna Stadler <luc@spreadshirt.net>

.changeset/clean-lobsters-brake.md

@@ -0,0 +1,7 @@
+---
+'@backstage/plugin-kubernetes-backend': minor
+---
+
+Allow fetching pod metrics limited by a `labelSelector`.
+
+This is used by the Kubernetes tab on a components' page and leads to much smaller responses being received from Kubernetes, especially with larger Kubernetes clusters.

plugins/kubernetes-backend/src/service/KubernetesFanOutHandler.test.ts

@@ -918,7 +918,7 @@ describe('getKubernetesObjectsByEntity', () => {
               {
                 errorType: 'FETCH_ERROR',
                 message:
-                  'request to https://fails/api/v1/pods?labelSelector=backstage.io/kubernetes-id=test-component failed, reason: socket error',
+                  'request to https://fails/api/v1/pods?labelSelector=backstage.io%2Fkubernetes-id%3Dtest-component failed, reason: socket error',
               },
             ],
           },

plugins/kubernetes-backend/src/service/KubernetesFanOutHandler.ts

@@ -283,7 +283,9 @@ export class KubernetesFanOutHandler {
             })),
             namespace,
           })
-          .then(result => this.getMetricsForPods(clusterDetailsItem, result))
+          .then(result =>
+            this.getMetricsForPods(clusterDetailsItem, labelSelector, result),
+          )
           .catch(
             (e): Promise<responseWithMetrics> =>
               e.name === 'FetchError'
@@ -365,6 +367,7 @@ export class KubernetesFanOutHandler {
 
   async getMetricsForPods(
     clusterDetails: ClusterDetails,
+    labelSelector: string,
     result: FetchResponseWrapper,
   ): Promise<responseWithMetrics> {
     if (clusterDetails.skipMetricsLookup) {
@@ -385,6 +388,7 @@ export class KubernetesFanOutHandler {
     const podMetrics = await this.fetcher.fetchPodMetricsByNamespaces(
       clusterDetails,
       namespaces,
+      labelSelector,
     );
 
     result.errors.push(...podMetrics.errors);

plugins/kubernetes-backend/src/service/KubernetesFetcher.ts

@@ -119,6 +119,7 @@ export class KubernetesClientBasedFetcher implements KubernetesFetcher {
   fetchPodMetricsByNamespaces(
     clusterDetails: ClusterDetails,
     namespaces: Set<string>,
+    labelSelector?: string,
   ): Promise<FetchResponseWrapper> {
     const fetchResults = Array.from(namespaces).map(async ns => {
       const [podMetrics, podList] = await Promise.all([
@@ -128,8 +129,9 @@ export class KubernetesClientBasedFetcher implements KubernetesFetcher {
           'v1beta1',
           'pods',
           ns,
+          labelSelector,
         ),
-        this.fetchResource(clusterDetails, '', 'v1', 'pods', ns),
+        this.fetchResource(clusterDetails, '', 'v1', 'pods', ns, labelSelector),
       ]);
       if (podMetrics.ok && podList.ok) {
         return topPods(
@@ -213,7 +215,7 @@ export class KubernetesClientBasedFetcher implements KubernetesFetcher {
     }
 
     if (labelSelector) {
-      url.search = `labelSelector=${labelSelector}`;
+      url.search = `labelSelector=${encode(labelSelector)}`;
     }
 
     return fetch(url, requestInit);

plugins/kubernetes-backend/src/types/types.ts

@@ -56,6 +56,7 @@ export interface KubernetesFetcher {
   fetchPodMetricsByNamespaces(
     clusterDetails: ClusterDetails,
     namespaces: Set<string>,
+    labelSelector?: string,
   ): Promise<FetchResponseWrapper>;
 }