Handling sessions with Firestore

This tutorial shows how to handle sessions on Cloud Run.

Many apps need session handling for authentication and user preferences. The Jetty framework comes with a memory-based implementation to perform this function. However, this implementation is unsuitable for an app that can be served from multiple instances, because the session that is recorded in one instance might differ from other instances. This tutorial shows how to handle sessions on Cloud Run.

The web app

This app displays greetings in different languages for every user. Returning users are always greeted in the same language.

Before your app can store preferences for a user, you need a way to store information about the current user in a session. This sample app uses a WebFilter to retrieve and update session data in Firestore.

@Override
public void init(FilterConfig config) throws ServletException {
  // Initialize local copy of datastore session variables.
  firestore = FirestoreOptions.getDefaultInstance().getService();
  sessions = firestore.collection("sessions");

  try {
    // Delete all sessions unmodified for over two days.
    Calendar cal = Calendar.getInstance();
    cal.setTime(new Date());
    cal.add(Calendar.HOUR, -48);
    Date twoDaysAgo = Calendar.getInstance().getTime();
    QuerySnapshot sessionDocs =
        sessions.whereLessThan("lastModified", dtf.format(twoDaysAgo)).get().get();
    for (QueryDocumentSnapshot snapshot : sessionDocs.getDocuments()) {
      snapshot.getReference().delete();
    }
  } catch (InterruptedException | ExecutionException e) {
    throw new ServletException("Exception initializing FirestoreSessionFilter.", e);
  }
}

The following diagram illustrates how Firestore handles sessions for the Cloud Run app.

The HttpServletRequest uses a cookie to store a unique ID for the local session, which corresponds to a document in Firestore with the session details.

Deleting sessions

Firestore doesn't delete old or expired sessions. You can delete session data in the Google Cloud console or implement an automated deletion strategy. If you use storage solutions for sessions such as Memcache or Redis, expired sessions are automatically deleted.

Running locally

1. Start the HTTP server:

   mvn jetty:run
   

2. View the app in your web browser:

   Cloud Shell

   In the Cloud Shell toolbar, click Web preview and select Preview on port 8080.

   Local machine

   In your browser, go to http://localhost:8080

   You see one of five greetings: "Hello World", "Hallo Welt", "Hola mundo", "Salut le Monde", or "Ciao Mondo." The language changes if you open the page in a different browser or in incognito mode. You can see and edit the session data in the Google Cloud console.

   

3. To stop the HTTP server, in your terminal window, press Control+C.

Deploying and running on Cloud Run

You can use the Cloud Run to build and deploy an app that runs reliably under heavy load and with large amounts of data.

1. In your terminal window, build and deploy an image of your code to Google Container Registry (GCR) with the Jib Maven plugin.

   mvn clean package jib:build

2. Deploy the app to Cloud Run:

      gcloud beta run deploy session-handling --image gcr.io/MY_PROJECT/session-handling 
   
            --platform managed --region us-central1 --memory 512M
      

   Replace MY_PROJECT with the ID of the Google Cloud project you created. Visit the URL returned by this command to see how session data persists between page loads.

Debugging the app

If you cannot connect to your Cloud Run app, check the following:

1. Check that the gcloud deploy commands successfully completed and didn't output any errors. If there were errors (for example, message=Build failed), fix them, and try deploying the Cloud Run app again.

2. In the Google Cloud console, go to the Logs Explorer page.

   Go to Logs Explorer page

   1. In the Recently selected resources drop-down list, click Cloud Run Application, and then click All module_id. You see a list of requests from when you visited your app. If you don't see a list of requests, confirm you selected All module_id from the drop-down list. If you see error messages printed to the Google Cloud console, check that your app's code matches the code in the section about writing the web app.

   2. Make sure that the Firestore API is enabled.