Load From CDN

package.json

@@ -55,7 +55,7 @@
     "uuid": "^9.0.1"
   },
   "dependencies": {
-    "@azure/app-configuration": "^1.6.1",
+    "@azure/app-configuration": "^1.8.0",
     "@azure/identity": "^4.2.1",
     "@azure/keyvault-secrets": "^4.7.0"
   }

src/EtagUrlPipelinePolicy.ts

@@ -0,0 +1,29 @@
+// Copyright (c) Microsoft Corporation.
+// Licensed under the MIT license.
+
+import { PipelinePolicy } from "@azure/core-rest-pipeline";
+
+export const ETAG_LOOKUP_HEADER = "Etag-Lookup";
+
+/**
+ * The pipeline policy that retrieves the etag from the request header and appends it to the request URL. After that the etag header is removed from the request.
+ * @remarks
+ * The policy position should be perCall.
+ * The App Configuration service will not recognize the etag query parameter in the url, but this can help to break the CDN cache as the cache entry is based on the URL.
+ */
+export class EtagUrlPipelinePolicy implements PipelinePolicy {
+    name: string = "AppConfigurationEtagUrlPolicy";
+
+    async sendRequest(request, next) {
+        if (request.headers.has(ETAG_LOOKUP_HEADER)) {
+            const etag = request.headers.get(ETAG_LOOKUP_HEADER);
+            request.headers.delete(ETAG_LOOKUP_HEADER);
+
+            const url = new URL(request.url);
+            url.searchParams.append("_", etag); // _ is a dummy query parameter to break the CDN cache
+            request.url = url.toString();
+        }
+
+        return next(request);
+    }
+}

src/index.ts

@@ -3,6 +3,6 @@
 
 export { AzureAppConfiguration } from "./AzureAppConfiguration.js";
 export { Disposable } from "./common/disposable.js";
-export { load } from "./load.js";
+export { load, loadFromCdn } from "./load.js";
 export { KeyFilter, LabelFilter } from "./types.js";
 export { VERSION } from "./version.js";

src/load.ts

@@ -6,9 +6,15 @@ import { AzureAppConfiguration } from "./AzureAppConfiguration.js";
 import { AzureAppConfigurationImpl } from "./AzureAppConfigurationImpl.js";
 import { AzureAppConfigurationOptions } from "./AzureAppConfigurationOptions.js";
 import { ConfigurationClientManager, instanceOfTokenCredential } from "./ConfigurationClientManager.js";
+import { EtagUrlPipelinePolicy } from "./EtagUrlPipelinePolicy.js";
 
 const MIN_DELAY_FOR_UNHANDLED_ERROR: number = 5000; // 5 seconds
 
+// Empty token credential to be used when loading from CDN
+const emptyTokenCredential: TokenCredential = {
+    getToken: async () => ({ token: "", expiresOnTimestamp: 0 })
+};
+
 /**
  * Loads the data from Azure App Configuration service and returns an instance of AzureAppConfiguration.
  * @param connectionString  The connection string for the App Configuration store.
@@ -41,7 +47,7 @@ export async function load(
     }
 
     try {
-        const appConfiguration = new AzureAppConfigurationImpl(clientManager, options);
+        const appConfiguration = new AzureAppConfigurationImpl(clientManager, options, credentialOrOptions === emptyTokenCredential);
         await appConfiguration.load();
         return appConfiguration;
     } catch (error) {
@@ -55,3 +61,32 @@ export async function load(
         throw error;
     }
 }
+
+/**
+ * Loads the data from a CDN and returns an instance of AzureAppConfiguration.
+ * @param cdnEndpoint  The URL to the CDN.
+ * @param appConfigOptions  Optional parameters.
+ */
+export async function loadFromCdn(cdnEndpoint: URL | string, options?: AzureAppConfigurationOptions): Promise<AzureAppConfiguration>;
+
+export async function loadFromCdn(
+    cdnEndpoint: string | URL,
+    appConfigOptions?: AzureAppConfigurationOptions
+): Promise<AzureAppConfiguration> {
+    if (appConfigOptions === undefined) {
+        appConfigOptions = { clientOptions: {}};
+    }
+
+    appConfigOptions.clientOptions = {
+        ...appConfigOptions.clientOptions,
+        // Specify the api version that supports sas token authentication
+        apiVersion: "2024-09-01-preview",
+        // Add etag url policy to append etag to the request url for breaking CDN cache
+        additionalPolicies: [
+            ...(appConfigOptions.clientOptions?.additionalPolicies || []),
+            { policy: new EtagUrlPipelinePolicy(), position: "perCall" }
+        ]
+    };
+
+    return await load(cdnEndpoint, emptyTokenCredential, appConfigOptions);
+}

src/requestTracing/constants.ts

@@ -49,6 +49,7 @@ export const REPLICA_COUNT_KEY = "ReplicaCount";
 
 // Tag names
 export const KEY_VAULT_CONFIGURED_TAG = "UsesKeyVault";
+export const CDN_USED_TAG = "CDN";
 export const FAILOVER_REQUEST_TAG = "Failover";
 
 // Compact feature tags

src/requestTracing/utils.ts

@@ -17,6 +17,7 @@ import {
     HOST_TYPE_KEY,
     HostType,
     KEY_VAULT_CONFIGURED_TAG,
+    CDN_USED_TAG,
     KUBERNETES_ENV_VAR,
     NODEJS_DEV_ENV_VAL,
     NODEJS_ENV_VAR,
@@ -36,6 +37,7 @@ export interface RequestTracingOptions {
     initialLoadCompleted: boolean;
     replicaCount: number;
     isFailoverRequest: boolean;
+    isCdnUsed: boolean;
     featureFlagTracing: FeatureFlagTracingOptions | undefined;
 }
 
@@ -48,6 +50,7 @@ export function listConfigurationSettingsWithTrace(
     const actualListOptions = { ...listOptions };
     if (requestTracingOptions.enabled) {
         actualListOptions.requestOptions = {
+            ...actualListOptions.requestOptions,
             customHeaders: {
                 [CORRELATION_CONTEXT_HEADER_NAME]: createCorrelationContextHeader(requestTracingOptions)
             }
@@ -67,6 +70,7 @@ export function getConfigurationSettingWithTrace(
 
     if (requestTracingOptions.enabled) {
         actualGetOptions.requestOptions = {
+            ...actualGetOptions.requestOptions,
             customHeaders: {
                 [CORRELATION_CONTEXT_HEADER_NAME]: createCorrelationContextHeader(requestTracingOptions)
             }
@@ -88,6 +92,7 @@ export function createCorrelationContextHeader(requestTracingOptions: RequestTra
     FFFeatures: Seed+Telemetry
     UsersKeyVault
     Failover
+    CDN
     */
     const keyValues = new Map<string, string | undefined>();
     const tags: string[] = [];
@@ -116,6 +121,9 @@ export function createCorrelationContextHeader(requestTracingOptions: RequestTra
     if (requestTracingOptions.isFailoverRequest) {
         tags.push(FAILOVER_REQUEST_TAG);
     }
+    if (requestTracingOptions.isCdnUsed) {
+        tags.push(CDN_USED_TAG);
+    }
     if (requestTracingOptions.replicaCount > 0) {
         keyValues.set(REPLICA_COUNT_KEY, requestTracingOptions.replicaCount.toString());
     }

test/exportedApi.ts

@@ -1,4 +1,4 @@
 // Copyright (c) Microsoft Corporation.
 // Licensed under the MIT license.
 
-export { load } from "../src";
+export { load, loadFromCdn } from "../src";

test/loadBalance.test.ts

@@ -6,10 +6,15 @@ import * as chaiAsPromised from "chai-as-promised";
 chai.use(chaiAsPromised);
 const expect = chai.expect;
 import { load } from "./exportedApi.js";
-import { MAX_TIME_OUT, restoreMocks, createMockedConnectionString, sleepInMs, createMockedEndpoint, mockConfigurationManagerGetClients, mockAppConfigurationClientLoadBalanceMode } from "./utils/testHelper.js";
+import { MAX_TIME_OUT, restoreMocks, createMockedConnectionString, createMockedKeyValue, sleepInMs, createMockedEndpoint, mockConfigurationManagerGetClients, mockAppConfigurationClientLoadBalanceMode } from "./utils/testHelper.js";
 import { AppConfigurationClient } from "@azure/app-configuration";
 import { ConfigurationClientWrapper } from "../src/ConfigurationClientWrapper.js";
 
+const mockedKVs = [
+    { value: "red", key: "app.settings.fontColor" },
+    { value: "40", key: "app.settings.fontSize" },
+    { value: "30", key: "app.settings.fontSize", label: "prod" }
+].map(createMockedKeyValue);
 const fakeEndpoint_1 = createMockedEndpoint("fake_1");
 const fakeEndpoint_2 = createMockedEndpoint("fake_2");
 const fakeClientWrapper_1 = new ConfigurationClientWrapper(fakeEndpoint_1, new AppConfigurationClient(createMockedConnectionString(fakeEndpoint_1)));
@@ -29,8 +34,8 @@ describe("load balance", function () {
 
     it("should load balance the request when loadBalancingEnabled", async () => {
         mockConfigurationManagerGetClients([fakeClientWrapper_1, fakeClientWrapper_2], false);
-        mockAppConfigurationClientLoadBalanceMode(fakeClientWrapper_1, clientRequestCounter_1);
-        mockAppConfigurationClientLoadBalanceMode(fakeClientWrapper_2, clientRequestCounter_2);
+        mockAppConfigurationClientLoadBalanceMode([mockedKVs], fakeClientWrapper_1, clientRequestCounter_1);
+        mockAppConfigurationClientLoadBalanceMode([mockedKVs], fakeClientWrapper_2, clientRequestCounter_2);
 
         const connectionString = createMockedConnectionString();
         const settings = await load(connectionString, {
@@ -66,8 +71,8 @@ describe("load balance", function () {
         clientRequestCounter_1.count = 0;
         clientRequestCounter_2.count = 0;
         mockConfigurationManagerGetClients([fakeClientWrapper_1, fakeClientWrapper_2], false);
-        mockAppConfigurationClientLoadBalanceMode(fakeClientWrapper_1, clientRequestCounter_1);
-        mockAppConfigurationClientLoadBalanceMode(fakeClientWrapper_2, clientRequestCounter_2);
+        mockAppConfigurationClientLoadBalanceMode([mockedKVs], fakeClientWrapper_1, clientRequestCounter_1);
+        mockAppConfigurationClientLoadBalanceMode([mockedKVs], fakeClientWrapper_2, clientRequestCounter_2);
 
         const connectionString = createMockedConnectionString();
         // loadBalancingEnabled is default to false

test/requestTracing.test.ts

@@ -7,7 +7,7 @@ chai.use(chaiAsPromised);
 const expect = chai.expect;
 import { MAX_TIME_OUT, HttpRequestHeadersPolicy, createMockedConnectionString, createMockedKeyValue, createMockedFeatureFlag, createMockedTokenCredential, mockAppConfigurationClientListConfigurationSettings, restoreMocks, sinon, sleepInMs } from "./utils/testHelper.js";
 import { ConfigurationClientManager } from "../src/ConfigurationClientManager.js";
-import { load } from "./exportedApi.js";
+import { load, loadFromCdn } from "./exportedApi.js";
 
 const CORRELATION_CONTEXT_HEADER_NAME = "Correlation-Context";
 
@@ -77,6 +77,30 @@ describe("request tracing", function () {
         sinon.restore();
     });
 
+    it("should have cdn tag in correlation-context header when loadFromCdn is used", async () => {
+        try {
+            await loadFromCdn(fakeEndpoint, {
+                clientOptions
+            });
+        } catch (e) { /* empty */ }
+        expect(headerPolicy.headers).not.undefined;
+        const correlationContext = headerPolicy.headers.get("Correlation-Context");
+        expect(correlationContext).not.undefined;
+        expect(correlationContext.includes("CDN")).eq(true);
+    });
+
+    it("should not have cdn tag in correlation-context header when load is used", async () => {
+        try {
+            await load(createMockedConnectionString(fakeEndpoint), {
+                clientOptions
+            });
+        } catch (e) { /* empty */ }
+        expect(headerPolicy.headers).not.undefined;
+        const correlationContext = headerPolicy.headers.get("Correlation-Context");
+        expect(correlationContext).not.undefined;
+        expect(correlationContext.includes("CDN")).eq(false);
+    });
+
     it("should detect env in correlation-context header", async () => {
         process.env.NODE_ENV = "development";
         try {

test/utils/testHelper.ts

@@ -105,12 +105,11 @@ function mockAppConfigurationClientListConfigurationSettings(pages: Configuratio
     });
 }
 
-function mockAppConfigurationClientLoadBalanceMode(clientWrapper: ConfigurationClientWrapper, countObject: { count: number }) {
-    const emptyPages: ConfigurationSetting[][] = [];
+function mockAppConfigurationClientLoadBalanceMode(pages: ConfigurationSetting[][], clientWrapper: ConfigurationClientWrapper, countObject: { count: number }) {
     sinon.stub(clientWrapper.client, "listConfigurationSettings").callsFake((listOptions) => {
         countObject.count += 1;
-        const kvs = _filterKVs(emptyPages.flat(), listOptions);
-        return getMockedIterator(emptyPages, kvs, listOptions);
+        const kvs = _filterKVs(pages.flat(), listOptions);
+        return getMockedIterator(pages, kvs, listOptions);
     });
 }