forbid duplicate cluster names in config

Signed-off-by: Jamie Klassen <jamie.klassen@broadcom.com>

.changeset/great-rats-collect.md

@@ -0,0 +1,7 @@
+---
+'@backstage/plugin-kubernetes-backend': minor
+---
+
+**BREAKING** The backend will fail to start if two clusters in the app-config
+have the same name. The requirement for unique names has been declared in the
+docs for some time, but is now enforced.

plugins/kubernetes-backend/src/cluster-locator/ConfigClusterLocator.test.ts

@@ -405,4 +405,25 @@ describe('ConfigClusterLocator', () => {
       `Invalid cluster 'cluster1': mock error`,
     );
   });
+
+  it('fails on duplicate cluster names', () => {
+    const config: Config = new ConfigReader({
+      clusters: [
+        {
+          name: 'cluster',
+          url: 'url',
+          authProvider: 'authProvider',
+        },
+        {
+          name: 'cluster',
+          url: 'url',
+          authProvider: 'authProvider',
+        },
+      ],
+    });
+
+    expect(() => ConfigClusterLocator.fromConfig(config, authStrategy)).toThrow(
+      `Duplicate cluster name 'cluster'`,
+    );
+  });
 });

plugins/kubernetes-backend/src/cluster-locator/ConfigClusterLocator.ts

@@ -35,12 +35,17 @@ export class ConfigClusterLocator implements KubernetesClustersSupplier {
     config: Config,
     authStrategy: AuthenticationStrategy,
   ): ConfigClusterLocator {
+    const clusterNames = new Set();
     return new ConfigClusterLocator(
       config.getConfigArray('clusters').map(c => {
         const authMetadataBlock = c.getOptional<{
           [ANNOTATION_KUBERNETES_AUTH_PROVIDER]?: string;
         }>('authMetadata');
         const name = c.getString('name');
+        if (clusterNames.has(name)) {
+          throw new Error(`Duplicate cluster name '${name}'`);
+        }
+        clusterNames.add(name);
         const authProvider =
           authMetadataBlock?.[ANNOTATION_KUBERNETES_AUTH_PROVIDER] ??
           c.getOptionalString('authProvider');