Silently fail when srv query fail

src/ConfigurationClientManager.ts

@@ -18,7 +18,9 @@ const SECRET_KEY_NAME = "Secret";
 const TRUSTED_DOMAIN_LABELS = [".azconfig.", ".appconfig."];
 const FALLBACK_CLIENT_REFRESH_EXPIRE_INTERVAL = 60 * 60 * 1000; // 1 hour in milliseconds
 const MINIMAL_CLIENT_REFRESH_INTERVAL = 30 * 1000; // 30 seconds in milliseconds
-const SRV_QUERY_TIMEOUT = 30 * 1000; // 30 seconds in milliseconds
+const DNS_RESOLVER_TIMEOUT = 1_000; // 1 second in milliseconds
+const DNS_RESOLVER_TRIES = 2;
+const MAX_RESOLVESRV_TIMES = 15;
 
 export class ConfigurationClientManager {
     #isFailoverable: boolean;
@@ -85,10 +87,11 @@ export class ConfigurationClientManager {
             this.#isFailoverable = false;
             return;
         }
-        if (this.#dns) {
+        if (this.#dns) { // dns module is already loaded
             return;
         }
 
+        // We can only know whether dns module is available during runtime.
         try {
             this.#dns = await import("dns/promises");
         } catch (error) {
@@ -142,20 +145,16 @@ export class ConfigurationClientManager {
     }
 
     async #discoverFallbackClients(host: string) {
-        let result;
-        let timeout;
+        let result: string[];
         try {
-            result = await Promise.race([
-                new Promise((_, reject) => timeout = setTimeout(() => reject(new Error("SRV record query timed out.")), SRV_QUERY_TIMEOUT)),
-                this.#querySrvTargetHost(host)
-            ]);
+            result = await this.#querySrvTargetHost(host);
         } catch (error) {
-            throw new Error(`Failed to build fallback clients, ${error.message}`);
-        } finally {
-            clearTimeout(timeout);
+            console.warn(`Failed to build fallback clients, ${error.message}`);
+            this.#lastFallbackClientRefreshTime = Date.now();
+            return; // swallow the error when srv query fails
         }
 
-        const srvTargetHosts = shuffleList(result) as string[];
+        const srvTargetHosts = shuffleList(result);
         const newDynamicClients: ConfigurationClientWrapper[] = [];
         for (const host of srvTargetHosts) {
             if (isValidEndpoint(host, this.#validDomain)) {
@@ -182,8 +181,9 @@ export class ConfigurationClientManager {
         const results: string[] = [];
 
         try {
+            const resolver = new this.#dns.Resolver({timeout: DNS_RESOLVER_TIMEOUT, tries: DNS_RESOLVER_TRIES});
             // Look up SRV records for the origin host
-            const originRecords = await this.#dns.resolveSrv(`${TCP_ORIGIN_KEY_NAME}.${host}`);
+            const originRecords = await resolver.resolveSrv(`${TCP_ORIGIN_KEY_NAME}.${host}`);
             if (originRecords.length === 0) {
                 return results;
             }
@@ -194,10 +194,9 @@ export class ConfigurationClientManager {
 
             // Look up SRV records for alternate hosts
             let index = 0;
-            // eslint-disable-next-line no-constant-condition
-            while (true) {
+            while (index < MAX_RESOLVESRV_TIMES) {
                 const currentAlt = `${ALT_KEY_NAME}${index}`;
-                const altRecords = await this.#dns.resolveSrv(`${currentAlt}.${TCP_KEY_NAME}.${originHost}`);
+                const altRecords = await resolver.resolveSrv(`${currentAlt}.${TCP_KEY_NAME}.${originHost}`);
                 if (altRecords.length === 0) {
                     break; // No more alternate records, exit loop
                 }