update

Author: zhiyuanliang-ms

src/AzureAppConfigurationImpl.ts

@@ -41,8 +41,8 @@ import { RequestTracingOptions, getConfigurationSettingWithTrace, listConfigurat
 import { FeatureFlagTracingOptions } from "./requestTracing/FeatureFlagTracingOptions.js";
 import { KeyFilter, LabelFilter, SettingSelector } from "./types.js";
 import { ConfigurationClientManager } from "./ConfigurationClientManager.js";
-import { getFixedBackoffDuration, calculateDynamicBackoffDuration } from "./failover.js";
-import { FailoverError, OperationError, isFailoverableError, isRetriableError } from "./error.js";
+import { getFixedBackoffDuration, calculateBackoffDuration } from "./failover.js";
+import { OperationError, isFailoverableError, isRetriableError } from "./error.js";
 
 type PagedSettingSelector = SettingSelector & {
     /**
@@ -357,7 +357,6 @@ export class AzureAppConfigurationImpl implements AzureAppConfiguration {
                     this.#isInitialLoadCompleted = true;
                     break;
                 } catch (error) {
-
                     if (!isRetriableError(error)) {
                         throw error;
                     }
@@ -369,7 +368,7 @@ export class AzureAppConfigurationImpl implements AzureAppConfiguration {
                     let backoffDuration = getFixedBackoffDuration(timeElapsed);
                     if (backoffDuration === undefined) {
                         postAttempts += 1;
-                        backoffDuration = calculateDynamicBackoffDuration(postAttempts);
+                        backoffDuration = calculateBackoffDuration(postAttempts);
                     }
                     await new Promise(resolve => setTimeout(resolve, backoffDuration));
                     console.warn("Failed to load configuration settings at startup. Retrying...");
@@ -697,7 +696,7 @@ export class AzureAppConfigurationImpl implements AzureAppConfiguration {
         }
 
         this.#clientManager.refreshClients();
-        throw new FailoverError("All fallback clients failed to get configuration settings.");
+        throw new Error("All fallback clients failed to get configuration settings.");
     }
 
     async #processKeyValues(setting: ConfigurationSetting<string>): Promise<[string, unknown]> {

src/ConfigurationClientWrapper.ts

@@ -2,7 +2,7 @@
 // Licensed under the MIT license.
 
 import { AppConfigurationClient } from "@azure/app-configuration";
-import { calculateDynamicBackoffDuration } from "./failover.js";
+import { calculateBackoffDuration } from "./failover.js";
 
 export class ConfigurationClientWrapper {
     endpoint: string;
@@ -21,7 +21,7 @@ export class ConfigurationClientWrapper {
             this.backoffEndTime = Date.now();
         } else {
             this.#failedAttempts += 1;
-            this.backoffEndTime = Date.now() + calculateDynamicBackoffDuration(this.#failedAttempts);
+            this.backoffEndTime = Date.now() + calculateBackoffDuration(this.#failedAttempts);
         }
     }
 }

src/error.ts

@@ -13,20 +13,21 @@ export class OperationError extends Error {
     }
 }
 
-/**
- * Error thrown when fail to perform failover.
- */
-export class FailoverError extends Error {
-    constructor(message: string) {
-        super(message);
-        this.name = "FailoverError";
-    }
-}
-
 export function isFailoverableError(error: any): boolean {
+    if (!isRestError(error)) {
+        return false;
+    }
     // ENOTFOUND: DNS lookup failed, ENOENT: no such file or directory
-    return isRestError(error) && (error.code === "ENOTFOUND" || error.code === "ENOENT" ||
-        (error.statusCode !== undefined && (error.statusCode === 401 || error.statusCode === 403 || error.statusCode === 408 || error.statusCode === 429 || error.statusCode >= 500)));
+    if (error.code == "ENOTFOUND" || error.code === "ENOENT"){
+        return true;
+    }
+    // 401 Unauthorized, 403 Forbidden, 408 Request Timeout, 429 Too Many Requests, 5xx Server Errors
+    if (error.statusCode !== undefined &&
+        (error.statusCode === 401 || error.statusCode === 403 || error.statusCode === 408 || error.statusCode === 429 || error.statusCode >= 500)) {
+        return true;
+    }
+
+    return false;
 }
 
 export function isRetriableError(error: any): boolean {

src/failover.ts

@@ -3,10 +3,9 @@
 
 const MIN_BACKOFF_DURATION = 30_000; // 30 seconds in milliseconds
 const MAX_BACKOFF_DURATION = 10 * 60 * 1000; // 10 minutes in milliseconds
-const MAX_SAFE_EXPONENTIAL = 30; // Used to avoid overflow. bitwise operations in JavaScript are limited to 32 bits. It overflows at 2^31 - 1.
 const JITTER_RATIO = 0.25;
 
-// Reference: https://github.com/Azure/AppConfiguration-DotnetProvider/blob/main/src/Microsoft.Extensions.Configuration.AzureAppConfiguration/Extensions/TimeSpanExtensions.cs#L14
+// The backoff duration algorithm is consistent with the .NET configuration provider's implementation.
 export function getFixedBackoffDuration(timeElapsed: number): number | undefined {
     if (timeElapsed <= 100_000) { // 100 seconds in milliseconds
         return 5_000; // 5 seconds in milliseconds
@@ -20,14 +19,14 @@ export function getFixedBackoffDuration(timeElapsed: number): number | undefined
     return undefined;
 }
 
-export function calculateDynamicBackoffDuration(failedAttempts: number) {
+export function calculateBackoffDuration(failedAttempts: number) {
     if (failedAttempts <= 1) {
         return MIN_BACKOFF_DURATION;
     }
 
     // exponential: minBackoff * 2 ^ (failedAttempts - 1)
-    const exponential = Math.min(failedAttempts - 1, MAX_SAFE_EXPONENTIAL);
-    let calculatedBackoffDuration = MIN_BACKOFF_DURATION * (1 << exponential);
+    // The right shift operator is not used in order to avoid potential overflow. Bitwise operations in JavaScript are limited to 32 bits.
+    let calculatedBackoffDuration = MIN_BACKOFF_DURATION * Math.pow(2, failedAttempts - 1);
     if (calculatedBackoffDuration > MAX_BACKOFF_DURATION) {
         calculatedBackoffDuration = MAX_BACKOFF_DURATION;
     }