grpc-js: Disallow pick_first as child of outlier_detection

packages/grpc-js/package.json

@@ -1,6 +1,6 @@
 {
   "name": "@grpc/grpc-js",
-  "version": "1.8.16",
+  "version": "1.8.17",
   "description": "gRPC Library for Node - pure JS implementation",
   "homepage": "https://grpc.io/",
   "repository": "https://github.com/grpc/grpc-node/tree/master/packages/grpc-js",

packages/grpc-js/src/load-balancer-outlier-detection.ts

@@ -113,6 +113,9 @@ export class OutlierDetectionLoadBalancingConfig implements LoadBalancingConfig
     failurePercentageEjection: Partial<FailurePercentageEjectionConfig> | null,
     private readonly childPolicy: LoadBalancingConfig[]
   ) {
+    if (childPolicy[0].getLoadBalancerName() === 'pick_first') {
+      throw new Error('outlier_detection LB policy cannot have a pick_first child policy');
+    }
     this.intervalMs = intervalMs ?? 10_000;
     this.baseEjectionTimeMs = baseEjectionTimeMs ?? 30_000;
     this.maxEjectionTimeMs = maxEjectionTimeMs ?? 300_000;

packages/grpc-js/src/resolver-dns.ts

@@ -276,7 +276,7 @@ class DnsResolver implements Resolver {
             } catch (err) {
               this.latestServiceConfigError = {
                 code: Status.UNAVAILABLE,
-                details: 'Parsing service config failed',
+                details: `Parsing service config failed with error ${(err as Error).message}`,
                 metadata: new Metadata(),
               };
             }

packages/grpc-js/test/test-outlier-detection.ts

@@ -360,6 +360,16 @@ describe('Outlier detection config validation', () => {
       }, /failure_percentage_ejection\.enforcement_percentage parse error: value out of range for percentage/);
     });
   });
+  describe('child_policy', () => {
+    it('Should reject a pick_first child_policy', () => {
+      const loadBalancingConfig = {
+        child_policy: [{pick_first: {}}]
+      };
+      assert.throws(() => {
+        OutlierDetectionLoadBalancingConfig.createFromJson(loadBalancingConfig);
+      }, /outlier_detection LB policy cannot have a pick_first child policy/);
+    });
+  });
 });
 
 describe('Outlier detection', () => {