fix(parameters): refresh AppConfig session token after 24 hrs (#1916)

* fix(parameters): refresh appconfig session after 24 hrs

* chore: revert change in test

Author: dreamorosi

packages/parameters/src/appconfig/AppConfigProvider.ts

@@ -10,6 +10,7 @@ import type {
   AppConfigGetOptions,
   AppConfigGetOutput,
 } from '../types/AppConfigProvider';
+import { APPCONFIG_TOKEN_EXPIRATION } from '../constants';
 
 /**
  * ## Intro
@@ -182,7 +183,10 @@ import type {
  */
 class AppConfigProvider extends BaseProvider {
   public client!: AppConfigDataClient;
-  protected configurationTokenStore = new Map<string, string>();
+  protected configurationTokenStore = new Map<
+    string,
+    { value: string; expiration: number }
+  >();
   protected valueStore = new Map<string, Uint8Array>();
   private application?: string;
   private environment: string;
@@ -270,23 +274,26 @@ class AppConfigProvider extends BaseProvider {
   /**
    * Retrieve a configuration from AWS AppConfig.
    *
+   * First we start the session and after that we retrieve the configuration from AppSync.
+   * When starting a session, the service returns a token that can be used to poll for changes
+   * for up to 24hrs, so we cache it for later use together with the expiration date.
+   *
+   * The value of the configuration is also cached internally because AppConfig returns an empty
+   * value if the configuration has not changed since the last poll. This way even if your code
+   * polls the configuration multiple times, we return the most recent value by returning the cached
+   * one if an empty response is returned by AppConfig.
+   *
    * @param {string} name - Name of the configuration or its ID
    * @param {AppConfigGetOptions} options - SDK options to propagate to `StartConfigurationSession` API call
    */
   protected async _get(
     name: string,
     options?: AppConfigGetOptions
   ): Promise<Uint8Array | undefined> {
-    /**
-     * The new AppConfig APIs require two API calls to return the configuration
-     * First we start the session and after that we retrieve the configuration
-     * We need to store { name: token } pairs to use in the next execution
-     * We also need to store { name : value } pairs because AppConfig returns
-     * an empty value if the session already has the latest configuration
-     * but, we don't want to return an empty value to our callers.
-     * {@link https://docs.aws.amazon.com/appconfig/latest/userguide/appconfig-retrieving-the-configuration.html}
-     **/
-    if (!this.configurationTokenStore.has(name)) {
+    if (
+      !this.configurationTokenStore.has(name) ||
+      this.configurationTokenStore.get(name)!.expiration <= Date.now()
+    ) {
       const sessionOptions: StartConfigurationSessionCommandInput = {
         ...(options?.sdkOptions || {}),
         ApplicationIdentifier: this.application,
@@ -303,20 +310,23 @@ class AppConfigProvider extends BaseProvider {
       if (!session.InitialConfigurationToken)
         throw new Error('Unable to retrieve the configuration token');
 
-      this.configurationTokenStore.set(name, session.InitialConfigurationToken);
+      this.configurationTokenStore.set(name, {
+        value: session.InitialConfigurationToken,
+        expiration: Date.now() + APPCONFIG_TOKEN_EXPIRATION,
+      });
     }
 
     const getConfigurationCommand = new GetLatestConfigurationCommand({
-      ConfigurationToken: this.configurationTokenStore.get(name),
+      ConfigurationToken: this.configurationTokenStore.get(name)?.value,
     });
 
     const response = await this.client.send(getConfigurationCommand);
 
     if (response.NextPollConfigurationToken) {
-      this.configurationTokenStore.set(
-        name,
-        response.NextPollConfigurationToken
-      );
+      this.configurationTokenStore.set(name, {
+        value: response.NextPollConfigurationToken,
+        expiration: Date.now() + APPCONFIG_TOKEN_EXPIRATION,
+      });
     } else {
       this.configurationTokenStore.delete(name);
     }

packages/parameters/src/constants.ts

@@ -2,6 +2,7 @@ const DEFAULT_MAX_AGE_SECS = 5;
 const TRANSFORM_METHOD_JSON = 'json';
 const TRANSFORM_METHOD_BINARY = 'binary';
 const TRANSFORM_METHOD_AUTO = 'auto';
+const APPCONFIG_TOKEN_EXPIRATION = 23 * 60 * 60 * 1000 + 45 * 60 * 1000; // 23 hrs 45 min
 
 /**
  * Transform methods for values retrieved by parameter providers.
@@ -22,6 +23,7 @@ const Transform = {
 } as const;
 
 export {
+  APPCONFIG_TOKEN_EXPIRATION,
   DEFAULT_MAX_AGE_SECS,
   TRANSFORM_METHOD_JSON,
   TRANSFORM_METHOD_BINARY,

packages/parameters/tests/unit/AppConfigProvider.test.ts

@@ -15,11 +15,13 @@ import { Uint8ArrayBlobAdapter } from '@smithy/util-stream';
 import { mockClient } from 'aws-sdk-client-mock';
 import { addUserAgentMiddleware } from '@aws-lambda-powertools/commons';
 import 'aws-sdk-client-mock-jest';
+import { APPCONFIG_TOKEN_EXPIRATION } from '../../src/constants';
 
 jest.mock('@aws-lambda-powertools/commons', () => ({
   ...jest.requireActual('@aws-lambda-powertools/commons'),
   addUserAgentMiddleware: jest.fn(),
 }));
+jest.useFakeTimers();
 
 describe('Class: AppConfigProvider', () => {
   const client = mockClient(AppConfigDataClient);
@@ -201,7 +203,10 @@ describe('Class: AppConfigProvider', () => {
       // Prepare
       class AppConfigProviderMock extends AppConfigProvider {
         public _addToStore(key: string, value: string): void {
-          this.configurationTokenStore.set(key, value);
+          this.configurationTokenStore.set(key, {
+            value,
+            expiration: Date.now() + APPCONFIG_TOKEN_EXPIRATION,
+          });
         }
 
         public _storeHas(key: string): boolean {
@@ -289,6 +294,56 @@ describe('Class: AppConfigProvider', () => {
       expect(result1).toBe(mockData);
       expect(result2).toBe(mockData);
     });
+
+    test('when the session token has expired, it starts a new session and retrieves the token', async () => {
+      // Prepare
+      const options: AppConfigProviderOptions = {
+        application: 'MyApp',
+        environment: 'MyAppProdEnv',
+      };
+      const provider = new AppConfigProvider(options);
+      const name = 'MyAppFeatureFlag';
+
+      const fakeInitialToken = 'aW5pdGlhbFRva2Vu';
+      const fakeSecondToken = 'bZ6pdGlhbFRva3Wk';
+      const fakeNextToken1 = 'bmV4dFRva2Vu';
+      const mockData = Uint8ArrayBlobAdapter.fromString('foo');
+      const mockData2 = Uint8ArrayBlobAdapter.fromString('bar');
+
+      client
+        .on(StartConfigurationSessionCommand)
+        .resolvesOnce({
+          InitialConfigurationToken: fakeInitialToken,
+        })
+        .resolvesOnce({
+          InitialConfigurationToken: fakeSecondToken,
+        })
+        .on(GetLatestConfigurationCommand, {
+          ConfigurationToken: fakeInitialToken,
+        })
+        .resolves({
+          Configuration: mockData,
+          NextPollConfigurationToken: fakeNextToken1,
+        })
+        .on(GetLatestConfigurationCommand, {
+          ConfigurationToken: fakeSecondToken,
+        })
+        .resolves({
+          Configuration: mockData2,
+          NextPollConfigurationToken: fakeNextToken1,
+        });
+      jest.setSystemTime(new Date('2022-03-10'));
+
+      // Act
+      const result1 = await provider.get(name, { forceFetch: true });
+      // Mock time skip of 24hrs
+      jest.setSystemTime(new Date('2022-03-11'));
+      const result2 = await provider.get(name, { forceFetch: true });
+
+      // Assess
+      expect(result1).toBe(mockData);
+      expect(result2).toBe(mockData2);
+    });
   });
 
   describe('Method: _getMultiple', () => {