In this environment, runtimes with predefined configuration and specified versions for various programming languages such as PHP, Go, Java, and Python are used to deploy applications on Google Cloud Platform. These runtimes also contain various libraries that provide additional functionalities for your application running on App engine. Unlike traditional hosting, the applications hosted on App engine cannot write files to the folder in the App engine. All files uploaded by the users should be saved to Google Cloud Storage via API and the application cannot write files such as error logs or session data. The application must be modified to use either a database such as Cloud SQL to do session tracking or Cloud Datastore to store these details.

The App engine provides some additional features that make applications scale automatically. The following are some of the additional features that your application can take advantage of:

• Multitenacy: This is an excellent feature for developing SAAS applications. This service helps a single site hosted on multiple domains to support multiple clients and partition their data across various services such as Datastore, Caching, and Task Queue. 
• Memcache: This is a scalable caching service that can store gigabytes of data in memory. Cache management can be automated via API and cache data can also be shared with other applications on the Google Cloud.
• Image API: The image API provides functions such as rotation, resizing, crop images, stitching images together, and also applying various enhancements to images.
• Cron Service: This service provides features to schedule tasks to run at regular intervals. The cron job can invoke an HTTP URL that will execute the tasks within a specified time limit based on the billing tier. 
• Search: The search API provides options to search and index the documents and data used by your application. This is one of the features that can help e-commerce websites because users mostly land on a product page or category page after searching the site. 
• Logs: The logging feature helps all applications hosted on your account to the information and errors. Google Cloud also internally logs requests, and this helps you analyze and handle the application issues easily and reduce your turnaround time.
• Task Queue: Applications can trigger some tasks asynchronously or outside of the request life cycle. This is one of the features that applications can take advantage of to boost their performance. Sending mails, logging events, and starting some transactions can be done outside of the request cycle.
• Traffic Splitting: Applications can take advantage of Traffic Splitting to do A/B testing. This will help e-commerce sites to track a new or beta features performance before making it available to all users.
• URL Fetch: This service helps clients access HTTP or HTTPS URLs to get a response and even save the response to Cloud Storage. If your application requires downloading or crawling and storing contents from various places on the Internet, this will be a handy feature. The requests are sent and responses are received through Google's infrastructure, and you can imagine the performance of your applications.

In addition to these features, the applications running on App engine can connect to Cloud SQL and other databases on Google Cloud. The apps can also connect to BigQuery and interact with various services such as Cloud Datastore and Cloud Storage.