Note: Java 8 has reached end of support on January 31, 2024. Your existing Java 8 applications will continue to run and receive traffic. However, App Engine might block re-deployment of applications that use runtimes after their end of support date. We recommend that you migrate to the latest supported version of Java.

How Requests are Routed

Region ID

The REGION_ID is an abbreviated code that Google assigns based on the region you select when you create your app. The code does not correspond to a country or province, even though some region IDs may appear similar to commonly used country and province codes. For apps created after February 2020, REGION_ID.r is included in App Engine URLs. For existing apps created before this date, the region ID is optional in the URL.

Learn more about region IDs.

This page describes how HTTP requests from users reach the appropriate version of a service. Requests can be routed in the following ways:

Routing with URLs
Routing with a dispatch file
Routing with Cloud Load Balancing

If you test your app using the local development server, the available routing and dispatch features are slightly different. To programmatically create URLs that work with both production and development servers, use the ModulesService.getVersionHostname method.

See routing in the development server to learn more.

Routing with URLs

Once your app is running in App Engine, you can use the following URL to send HTTP requests to the app:
https://PROJECT_ID.REGION_ID.r.appspot.com

where PROJECT_ID is the ID of the Google Cloud project that contains the app.

This URL sends requests to your app's default service at the version that you have configured to receive traffic.

URLs for services and versions

If you create more than one service in your app, each service has its own URL. Each version of a service also has its own URL, so you can deploy and test a new version before configuring that version to receive traffic.

The URLs for specific services and versions are in the following form:

VERSION-dot-SERVICE-dot-PROJECT_ID.REGION_ID.r.appspot.com

You can omit VERSION-dot- if you don't need to target a specific version.

To retrieve the IDs of your app's services and versions, you can use any of the following tools:

Console

In the Google Cloud console, you can view the corresponding Instances, Services, and Versions pages.

gcloud

Run the gcloud app instances list command to list the resource IDs within a specific Google Cloud project.

API

To programmatically retrieve resource IDs, see the list methods in the Admin API.

Example URLs

Here are some examples of URLs for App Engine, showing both the appspot.com domain that App Engine assigns to your app and a custom domain, which you can set up for your app.

Sends the request to an available instance of the default service:
```
https://PROJECT_ID.REGION_ID.r.appspot.com
https://CUSTOM_DOMAIN
```
Requests are received by any version that is configured for traffic in the default service.
Sends a request to an available instance of a specific service:
```
https://SERVICE_ID-dot-PROJECT_ID.REGION_ID.r.appspot.com
https://SERVICE_ID.CUSTOM_DOMAIN
```
Requests are received by any version that is configured for traffic in the targeted service. If the service that you are targeting does not exist, the request gets soft routed.
Sends a request to an available instance of a specific version in the

default service:
```
https://VERSION_ID-dot-default-dot-PROJECT_ID.REGION_ID.r.appspot.com
https://VERSION_ID.CUSTOM_DOMAIN
```
When a service is not targeted, requests are sent to the default service.

Soft routing

If a request matches the PROJECT_ID.REGION_ID.r.appspot.com portion of the hostname, but includes a service, version, or instance name that does not exist, then the request is routed to the default service. Soft routing does not apply to custom domains; requests to them will return a HTTP 404 status code if the hostname is invalid.

Targeted routing

The following URL patterns are guaranteed to reach their target, if they exist. These requests are never intercepted and rerouted by the patterns that you have defined in your dispatch file:

Sends the request to an available instance of a specific service and version:


https://VERSION-dot-SERVICE-dot-PROJECT_ID.REGION_ID.r.appspot.com
https://VERSION_ID.SERVICE_ID.PROJECT_ID.CUSTOM_DOMAIN

If you are using manually-scaled services, you can target and send a request to a instance by including the instance ID. The instance ID is an integer in the range from 0 up to the total number of instances that are running, and can be specified as follows:

Sends a request to a specific service and version within a specific instance:
```
https://INSTANCE_ID-dot-VERSION_ID-dot-SERVICE_ID-dot-PROJECT_ID.REGION_ID.r.appspot.com
https://INSTANCE_ID.VERSION_ID.SERVICE_ID.CUSTOM_DOMAIN
```
Note: Targeting an instance is not supported in services that are configured for auto scaling or basic scaling. The instance ID must be an integer in the range from 0, up to the total number of instances running. Regardless of your scaling type or instance class, it is not possible to send a request to a specific instance without targeting a service or version within that instance.

Routing with a dispatch file

You can create a dispatch file to override App Engine's URL-based routing rules and define your own custom routing rules. With a dispatch file, you can send incoming requests to a specific service based on the path or host name in the request URL.

Creating a dispatch file

To create a dispatch file:

Create a file named dispatch.yaml in the same directory used for the other configuration files, such as app.yaml.
Define routing rules in the file as described see the dispatch.yaml reference.

Note the following about the routing rules:

You can define up to 20 routing rules. Each rule must contain the url and service elements.
The rules must use HTTP URL patterns that include the "." notation for separating subdomains. URLs defined with the HTTPS "-dot-" notation are not supported.
The rules also apply to the URLs that you define in your cron file.

For example, you can create a dispatch file to route mobile requests like https://simple-sample.uc.r.appspot.com/mobile/ to a mobile frontend, and route worker requests like https://simple-sample.uc.r.appspot.com/work/ to a static backend:

dispatch:
  # Send all mobile traffic to the mobile frontend.
  - url: "*/mobile/*"
    service: mobile-frontend

  # Send all work to the one static backend.
  - url: "*/work/*"
    service: static-backend

Deploying the dispatch file

To deploy the dispatch configuration file without otherwise altering the currently serving version, use one of the following commands in the directory containing your dispatch file, depending on your environment:

gcloud

gcloud app deploy dispatch.yaml

Maven

mvn appengine:deployDispatch dispatch.yaml

Gradle

gradle appengineDeployDispatch dispatch.yaml

IDE

If you use IntelliJ or Eclipse, you select the individual configuration files to be deployed using the deployment form.

Routing with Cloud Load Balancing

Cloud Load Balancing is a separate product that enables advanced network configurations for all of your applications running on Google Cloud.

When HTTP(S) Load Balancing is enabled for serverless apps, you can:

Configure your serverless app to serve from a dedicated IPv4 and/or IPv6 IP address that is not shared with other services.
Reuse the same SSL certificates and private keys that you use for Compute Engine, Google Kubernetes Engine and Cloud Storage. This eliminates the need to manage separate certificates for serverless apps.

The load balancer does not interfere or interact with routing rules in your dispatch.yaml file. The dispatch.yaml rules are not evaluated until a serverless NEG directs traffic to App Engine.

Note the following:

We recommend that you use ingress controls so that your app only receives requests sent from the load balancer (and the VPC if you use it). Otherwise, users can use your app's App Engine URL to bypass the load balancer, Google Cloud Armor security policies, SSL certificates, and private keys that are passed through the load balancer.

Routing in the development server

Discovering instance addresses

The local development server creates all instances at startup. Note that at this time basic scaling instances are not supported on the local development server. Every instance that is created is assigned its own port. The port assignments appear in the server's log message stream. Web clients can communicate with a particular instance by targeting its port. Only one instance (and port) is created for automatic scaled services. It looks like this in the server log (note that services were previously called modules):

INFO: Module instance service-auto is running at http://localhost:37251/

A unique port is assigned to each instance of a manual scaled service:

INFO: Module instance service-manual instance 0 is running at http://localhost:43190/
INFO: Module instance service-manual instance 1 is running at http://localhost:52642/

In addition, each manual scaled service is assigned one extra port so clients can access the service without specifying a specific instance. Requests to this port are automatically routed to one of the configured instances:

INFO: Module instance service-manual is running at http://localhost:12361/

The following table shows how these services can be called in the development server and in the App Engine environment:

Service	Instance	Development server address	App Engine address
service-auto	(not used)	`http://localhost:37251/`	`https://v1-dot-service-auto-dot-PROJECT_ID.REGION_ID.r.appspot.com/`
service-manual	0	`http://localhost:43190/`	`https://0-dot-v1-dot-service-manual-dot-PROJECT_ID.REGION_ID.r.appspot.com/`

is used by the local development server. For details, see Apache Maven or Gradle.

Dispatch files

All dispatch files are ignored when running the local development server. The only way to target instances is through their ports.

Restricting access to a service

All services are public by default. If you want to restrict access to a service, add the <role-name>admin</role-name> element to its security constraint

Additional details about App Engine URLs

Understanding the Region ID in URLs

You can use the following tools to see the region ID of your app:

Console

In the Google Cloud console, you can view the URLs for your app's Instances, Services, and Versions.

All of these URLs include the region ID.

gcloud

When you deploy an app or service, the gcloud app deploy command displays the URL after the deployment succeeds. This URL includes the region ID.

To view the URL for a service that is already deployed:

Enter the gcloud app versions list command to list the versions of a specific service. For example, to list the versions of the default service, enter gcloud app versions list --service=default.
Enter the gcloud app versions describe command. The output of that command includes the version URL with the app's region ID. For example, to describe version 20191023t101741 for the default service, enter gcloud app versions describe 20191023t101741 --service=default

Domain name is included in the request data

The domain name used for the request is included in the request data that is passed to your app. Therefore, you can use the request data to control how your app responds based on the domain name in the request. For example, if you want to redirect to an official domain, you can code your app to check the Host request header and then respond accordingly based on the domain name.