Firebase Admin SDK on app engine standard - google-app-engine

Question

is it possible to use Firebase on app engine standard environment? I am aware that the standard environment threading capabilities are very limited and since the Firebase SDK runs a background synchronization thread it might not be compatible. I've gave it a try and I've encountered the following error, which I can't seem to overcome:
java.security.AccessControlException: access denied ("java.lang.RuntimePermission" "modifyThreadGroup")
Here is the servlet code:
public class GeneratorServlet extends HttpServlet {
FirebaseDatabase database = null;
#Override
public void init(ServletConfig config) {
// ClassLoader classloader = Thread.currentThread().getContextClassLoader();
// InputStream serviceAccount = classloader.getResourceAsStream("serviceAccountKey.json");
FirebaseOptions options = new FirebaseOptions.Builder()
.setCredential(FirebaseCredentials.applicationDefault())
// .setCredential(FirebaseCredentials.fromCertificate(serviceAccount))
.setDatabaseUrl("https://app-name.firebaseio.com/")
.build();
FirebaseApp defaultApp = FirebaseApp.initializeApp(options);
this.database = FirebaseDatabase.getInstance(defaultApp);
}
#Override
public void doGet(HttpServletRequest req, HttpServletResponse resp) throws IOException {
PrintWriter out = resp.getWriter();
out.println(this.database);
this.loadData();
}
private void loadData() {
// The following line throws the error
DatabaseReference ref = this.database.getReference("/publiclyReadable");
}
}
Am I doing it wrong or is it caused by the limitations of the standard environment? I chose the standard environment over flexible because flexible version is not recommended for a production use yet.
Thanks, Jan
Edit:
appengine-web.xml
<?xml version="1.0" encoding="utf-8"?>
<appengine-web-app xmlns="http://appengine.google.com/ns/1.0">
<application>doctor-appointment-system</application>
<version>0</version>
<threadsafe>true</threadsafe>
<instance-class>B1</instance-class>
<manual-scaling>
<instances>1</instances>
</manual-scaling>
<system-properties>
<property name="java.util.logging.config.file" value="WEB-INF/logging.properties"/>
</system-properties>
</appengine-web-app>
Edit:
web.xml
<?xml version="1.0" encoding="utf-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://java.sun.com/xml/ns/javaee"
xmlns:web="http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd"
xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd"
version="2.5">
<servlet>
<servlet-name>generator</servlet-name>
<servlet-class>com.example.bookingtimes.GeneratorServlet</servlet-class>
</servlet>
<servlet>
<servlet-name>generatorinfo</servlet-name>
<servlet-class>com.example.bookingtimes.GeneratorInfoServlet</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>generator</servlet-name>
<url-pattern>/times/generate</url-pattern>
</servlet-mapping>
<servlet-mapping>
<servlet-name>generatorinfo</servlet-name>
<url-pattern>/times/change</url-pattern>
</servlet-mapping>
</web-app>
build.gradle:
buildscript { // Configuration for building
repositories {
jcenter()
mavenCentral()
}
dependencies {
classpath 'com.google.cloud.tools:appengine-gradle-plugin:+'
}
}
repositories { // repositories for Jar's you access in your code
maven {
url 'https://maven-central.storage.googleapis.com'
}
jcenter()
mavenCentral()
}
apply plugin: 'java' // standard Java tasks
apply plugin: 'war' // standard Web Archive plugin
apply plugin: 'com.google.cloud.tools.appengine' // App Engine tasks
dependencies {
providedCompile group: 'javax.servlet', name: 'servlet-api', version: '2.5'
compile 'com.google.appengine:appengine:+'
compile 'com.google.firebase:firebase-admin:4.1.0'
}
appengine { // App Engine tasks configuration
run { // local (dev_appserver) configuration (standard environments only)
port = 8080 // default
}
deploy {
stopPreviousVersion = true // default - stop the current version
promote = true // default - & make this the current version
}
}
group = 'com.example.appengine'
version = '0.1'
sourceCompatibility = 1.7
targetCompatibility = 1.7

Answer 1

The Firebase Database client can be used on App Engine Standard Environment, as long as you put it in manual scaling mode. See the documentation on cloud.google.com.
We recently fixed a problem when using the SDK on App Engine (release notes), so be sure to use the latest version.

Answer 2

I switched to App Engine Flexible (which was straightforward) and everything is working now.