backstage/.changeset/hot-items-smoke.md

@backstage/plugin-kubernetes-backend

@backstage/plugin-kubernetes-backend
minor

BREAKING Custom cluster suppliers need to cache their getClusters result

To allow custom KubernetesClustersSupplier instances to refresh the list of clusters the getClusters method is now called whenever the list of clusters is needed.

Existing KubernetesClustersSupplier implementations will need to ensure that getClusters can be called frequently and should return a cached result from getClusters instead.

For example, here's a simple example of a custom supplier in packages/backend/src/plugins/kubernetes.ts:

-import { KubernetesBuilder } from '@backstage/plugin-kubernetes-backend';
+import {
+  ClusterDetails,
+  KubernetesBuilder,
+  KubernetesClustersSupplier,
+} from '@backstage/plugin-kubernetes-backend';
 import { Router } from 'express';
 import { PluginEnvironment } from '../types';
+import { Duration } from 'luxon';
+
+export class CustomClustersSupplier implements KubernetesClustersSupplier {
+  constructor(private clusterDetails: ClusterDetails[] = []) {}
+
+  static create(refreshInterval: Duration) {
+    const clusterSupplier = new CustomClustersSupplier();
+    // setup refresh, e.g. using a copy of https://github.com/backstage/backstage/blob/master/plugins/search-backend-node/src/runPeriodically.ts
+    runPeriodically(
+      () => clusterSupplier.refreshClusters(),
+      refreshInterval.toMillis(),
+    );
+    return clusterSupplier;
+  }
+
+  async refreshClusters(): Promise<void> {
+    this.clusterDetails = []; // fetch from somewhere
+  }
+
+  async getClusters(): Promise<ClusterDetails[]> {
+    return this.clusterDetails;
+  }
+}

 export default async function createPlugin(
   env: PluginEnvironment,
 ): Promise<Router> {
-  const { router } = await KubernetesBuilder.createBuilder({
+  const builder = await KubernetesBuilder.createBuilder({
     logger: env.logger,
     config: env.config,
-  }).build();
+  });
+  builder.setClusterSupplier(
+    CustomClustersSupplier.create(Duration.fromObject({ minutes: 60 })),
+  );
+  const { router } = await builder.build();