Handling sessions with Firestore

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Many apps need session handling for authentication and user preferences. Sinatra 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 on one instance might differ from other instances. This tutorial shows how to handle sessions on App Engine.

Objectives

• Write the app.
• Run the app locally.
• Deploy the app on App Engine.

Costs

In this document, you use the following billable components of Google Cloud:

• App Engine
• Firestore

To generate a cost estimate based on your projected usage, use the pricing calculator. New Google Cloud users might be eligible for a free trial.

When you finish the tasks that are described in this document, you can avoid continued billing by deleting the resources that you created. For more information, see Clean up.

Before you begin

1. Sign in to your Google Cloud account. If you're new to Google Cloud, create an account to evaluate how our products perform in real-world scenarios. New customers also get $300 in free credits to run, test, and deploy workloads.

2. In the Google Cloud console, on the project selector page, select or create a Google Cloud project.

   Note: If you don't plan to keep the resources that you create in this procedure, create a project instead of selecting an existing project. After you finish these steps, you can delete the project, removing all resources associated with the project.

   Go to project selector

3. Make sure that billing is enabled for your Google Cloud project.

4. Enable the Firestore API.

   Enable the API

5. In the Google Cloud console, on the project selector page, select or create a Google Cloud project.

   Note: If you don't plan to keep the resources that you create in this procedure, create a project instead of selecting an existing project. After you finish these steps, you can delete the project, removing all resources associated with the project.

   Go to project selector

6. Make sure that billing is enabled for your Google Cloud project.

7. Enable the Firestore API.

   Enable the API

8. Prepare your development environment.

Setting up the project

1. In your terminal window, start in a directory of your choosing and create a new directory named sessions. All of the code for this tutorial is inside the sessions directory.

2. Change into the sessions directory:

   cd sessions
   

3. Initialize the Gemfile:

   bundle init
   

4. Append the following to the resulting Gemfile:

   gem "google-cloud-firestore", "~> 2.0"
   gem "sinatra", "~> 2.0"

   The Gemfile lists any non-standard Ruby libraries your app needs App Engine to load for it:

   • google-cloud-firestore is the Ruby client for the Firestore API.

   • Sinatra is the Ruby web framework used for the app.

5. Install the dependencies:

   bundle install
   

Writing the web app

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

• With a text editor, create a file called app.rb in the sessions directory with the following content:

  require "sinatra"
  
  require_relative "firestore_session"
  
  use Rack::Session::FirestoreSession
  
  set :greetings, ["Hello World", "Hallo Welt", "Ciao Mondo", "Salut le Monde", "Hola Mundo"]
  
  get "/" do
    session[:greeting] ||= settings.greetings.sample
    session[:views] ||= 0
    session[:views] += 1
    "<h1>#{session[:views]} views for \"#{session[:greeting]}\"</h1>"
  end

Creating the session store

Before your app can store preferences for a user, you need a way to store information about the current user in a session. The following diagram illustrates how Firestore handles sessions for the App Engine app.

Sinatra has built-in support for saving session data to a cookie. To save to Firestore instead, you have to define your own Rack::Session object.

• In the sessions directory, create a file called firestore_session.rb with the following content:

  require "google/cloud/firestore"
  require "rack/session/abstract/id"
  
  module Rack
    module Session
      class FirestoreSession < Abstract::Persisted
        def initialize app, options = {}
          super
  
          @firestore = Google::Cloud::Firestore.new
          @col = @firestore.col "sessions"
        end
  
        def find_session _req, session_id
          return [generate_sid, {}] if session_id.nil?
  
          doc = @col.doc session_id
          fields = doc.get.fields || {}
          [session_id, stringify_keys(fields)]
        end
  
        def write_session _req, session_id, new_session, _opts
          doc = @col.doc session_id
          doc.set new_session, merge: true
          session_id
        end
  
        def delete_session _req, session_id, _opts
          doc = @col.doc session_id
          doc.delete
          generate_sid
        end
  
        def stringify_keys hash
          new_hash = {}
          hash.each do |k, v|
            new_hash[k.to_s] =
              if v.is_a? Hash
                stringify_keys v
              else
                v
              end
          end
          new_hash
        end
      end
    end
  end

Note: Sinatra supports various options for session storage. Firestore is a persistent, distributed, transactional database. Often, it's more appropriate to choose a different storage solution for sessions such as Memcache or Redis, whose designs might result in faster operation for this use case.

Deleting sessions

As written, this app doesn't delete old or expired sessions. You can delete session data in the Google Cloud console, or you could implement an automated deletion strategy.

Running locally

1. Start the HTTP server:

   bundle exec ruby app.rb
   

2. View the app in your web browser.

   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 App Engine

You can use the App Engine standard environment to build and deploy an app that runs reliably under heavy load and with large amounts of data.

This tutorial uses the App Engine standard environment to deploy the server.

1. In your terminal window, create an app.yaml file and paste the following into the file:

   runtime: ruby25
   entrypoint: bundle exec ruby app.rb

2. Deploy the app on App Engine:

   gcloud app deploy
   

3. View the live app at the following URL, where PROJECT_ID is your Google Cloud project ID:

   https://PROJECT_ID.appspot.com

The greeting is now delivered by a web server running on an App Engine instance.

Debugging the app

If you cannot connect to your App Engine 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 App Engine 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 App Engine 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.

Clean up

Delete the project

Caution: Deleting a project has the following effects:

• Everything in the project is deleted. If you used an existing project for the tasks in this document, when you delete it, you also delete any other work you've done in the project.
• Custom project IDs are lost. When you created this project, you might have created a custom project ID that you want to use in the future. To preserve the URLs that use the project ID, such as an appspot.com URL, delete selected resources inside the project instead of deleting the whole project.

If you plan to explore multiple architectures, tutorials, or quickstarts, reusing projects can help you avoid exceeding project quota limits.

1. In the Google Cloud console, go to the Manage resources page.

   Go to Manage resources

2. In the project list, select the project that you want to delete, and then click Delete.
3. In the dialog, type the project ID, and then click Shut down to delete the project.

Delete the App Engine instance

1. In the Google Cloud console, go to the Versions page for App Engine.

   Go to Versions

2. Select the checkbox for the non-default app version that you want to delete.
   Note: The only way you can delete the default version of your App Engine app is by deleting your project. However, you can stop the default version in the Google Cloud console. This action shuts down all instances associated with the version. You can restart these instances later if needed.

   In the App Engine standard environment, you can stop the default version only if your app has manual or basic scaling.

3. To delete the app version, click Delete.

What's next

• Try more Cloud Functions tutorials.
• Learn more about App Engine.
• Try Cloud Run, which lets you run stateless containers on a fully managed environment or in your own Google Kubernetes Engine cluster.