[main] Adding round robin retry for snippet script src loading (#2131)

tools/applicationinsights-web-snippet/src/snippet.ts

@@ -183,6 +183,19 @@ declare var cfg:ISnippetConfig;
 
  return envelope;
  }
+
+ let domainRetryIndex = -1;
+ let domainRetryCount = 0;
+ let domains = [
+ "js.monitor.azure.com",
+ "js.cdn.applicationinsights.io",
+ "js.cdn.monitor.azure.com",
+ "js0.cdn.applicationinsights.io",
+ "js0.cdn.monitor.azure.com",
+ "js2.cdn.applicationinsights.io",
+ "js2.cdn.monitor.azure.com",
+ "az416426.vo.msecnd.net" // this domain is supported but not recommended
+ ]
 
  // Assigning these to local variables allows them to be minified to save space:
  let targetSrc : string = (aiConfig as any)["url"] || cfg.src
@@ -194,12 +207,31 @@ declare var cfg:ISnippetConfig;
  });
  // let message = "Load Version 2 SDK instead to support IE"; // where to report this error?
  }
+
+ if (cfg.cr !== false){
+ for (var i = 0; i < domains.length; i++){
+ if (targetSrc.indexOf(domains[i]) > 0){
+ domainRetryIndex = i;
+ break;
+ }
+ }
+ }
+
  const _handleError = (evt?: any) => {
- loadFailed = true;
  appInsights.queue = []; // Clear the queue
  if (!handled) {
- handled = true;
- _reportFailure(targetSrc);
+ // start retry
+ if (domainRetryIndex >= 0 && domainRetryCount + 1 < domains.length){ // domainRetryIndex will be negative when client using own domain (the supported domain list is defined above)
+ let nextIdx = (domainRetryIndex + domainRetryCount + 1) % domains.length;
+ _createScript(targetSrc.replace(/^(.*\/\/)([\w\.]*)(\/.*)$/, function (_all, http, domain, qs) {
+ return http + domains[nextIdx] + qs;
+ }));
+ domainRetryCount += 1;
+ } else {
+ handled = true;
+ loadFailed = true;
+ _reportFailure(targetSrc);
+ }
  }
  }
 
@@ -213,11 +245,12 @@ declare var cfg:ISnippetConfig;
  }
  }, 500);
  }
+ loadFailed = false;
  }
 
- const _createScript = () => {
+ const _createScript = (src: string) => {
  let scriptElement : HTMLElement = doc.createElement(scriptText);
- (scriptElement as any)["src"] = targetSrc;
+ (scriptElement as any)["src"] = src;
  // Allocate Cross origin only if defined and available
  let crossOrigin = cfg[strCrossOrigin];
  if ((crossOrigin || crossOrigin === "") && scriptElement[strCrossOrigin] != strUndefined) {
@@ -232,20 +265,21 @@ declare var cfg:ISnippetConfig;
  }
  };
 
- return scriptElement;
- }
+ if (cfg.ld && cfg.ld < 0) {
+ // if user wants to append tag to document head, blocking page load
+ let headNode = doc.getElementsByTagName("head")[0];
+ headNode.appendChild(scriptElement);
+ } else {
+ setTimeout(function () {
+ // Attempts to place the script tag in the same location as the first script on the page
+ doc.getElementsByTagName(scriptText)[0].parentNode.appendChild(scriptElement);
+ }, cfg.ld || 0);
+ }
+
 
- let theScript = _createScript();
- if (cfg.ld && cfg.ld < 0) {
- // if user wants to append tag to document head, blocking page load
- let headNode = doc.getElementsByTagName("head")[0];
- headNode.appendChild(theScript);
- } else {
- setTimeout(function () {
- // Attempts to place the script tag in the same location as the first script on the page
- doc.getElementsByTagName(scriptText)[0].parentNode.appendChild(theScript);
- }, cfg.ld || 0);
+ return scriptElement;
  }
+ _createScript(targetSrc);
  }
 
  // capture initial cookie

tools/applicationinsights-web-snippet/src/type.ts

@@ -8,6 +8,7 @@ export interface ISnippetConfig {
  crossOrigin?: string;
  onInit?: any;
  cfg: IConfiguration;
+ cr?: boolean; // cdn retry would be proceed if ture
 }
 
 export interface Fields {