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Using the Modules API

The Modules API provides functions that return information about the current operating environment (module, version, and instance).

The Modules API also has functions that retrieve the address of a module, a version, or an instance. This allows an application to send requests from one instance to another, in both the development and production environments.

The following code sample shows how to get the module name and instance id for a request:

  import 
  
 com.google.appengine.api.modules. ModulesService 
 
 ; 
 import 
  
 com.google.appengine.api.modules. ModulesServiceFactory 
 
 ; 
  ModulesService 
 
  
 modulesApi 
  
 = 
  
  ModulesServiceFactory 
 
 . 
 getModulesService 
 (); 
 // Get the service name handling the current request. 
 String 
  
 currentModuleName 
  
 = 
  
 modulesApi 
 . 
  getCurrentModule 
 
 (); 
 // Get the instance handling the current request. 
 int 
  
 currentInstance 
  
 = 
  
 modulesApi 
 . 
 getCurrentInstance 
 ();

The instance ID of an automatic scaled module will be returned as a unique base64 encoded value, e.g. e4b565394caa .

You can communicate between modules in the same app by fetching the hostname of the target module:

The following code sample shows how to get the module name and instance id for a request:

  import 
  
 com.google.appengine.api.modules. ModulesService 
 
 ; 
 import 
  
 com.google.appengine.api.modules. ModulesServiceFactory 
 
 ; 
 import 
  
 java.net.MalformedURLException 
 ; 
 import 
  
 java.net.URL 
 ; 
 import 
  
 java.io.BufferedReader 
 ; 
 import 
  
 java.io.InputStreamReader 
 ; 
 import 
  
 java.io.IOException 
 ; 
 // ... 
  ModulesService 
 
  
 modulesApi 
  
 = 
  
  ModulesServiceFactory 
 
 . 
 getModulesService 
 (); 
 // ... 
  
 try 
  
 { 
  
 URL 
  
 url 
  
 = 
  
 new 
  
 URL 
 ( 
 "http://" 
  
 + 
  
 modulesApi 
 . 
  getVersionHostname 
 
 ( 
 "my-backend-service" 
 , 
 "v1" 
 ) 
  
 + 
  
 "/fetch-stats" 
 ); 
  
 BufferedReader 
  
 reader 
  
 = 
  
 new 
  
 BufferedReader 
 ( 
  
 new 
  
 InputStreamReader 
 ( 
 url 
 . 
 openStream 
 ())); 
  
 String 
  
 line 
 ; 
  
 while 
  
 (( 
 line 
  
 = 
  
 reader 
 . 
 readLine 
 ()) 
  
 != 
  
 null 
 ) 
  
 { 
  
 // Do something... 
  
 } 
  
 reader 
 . 
 close 
 (); 
  
 } 
  
 catch 
  
 ( 
 MalformedURLException 
  
 e 
 ) 
  
 { 
  
 // ... 
  
 } 
  
 catch 
  
 ( 
 IOException 
  
 e 
 ) 
  
 { 
  
 // ... 
  
 }

You can also use the URL Fetch service.

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Using the Modules API