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App Engine connectivity questions

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This page contains answers to common App Engine connectivity questions, including questions related to using Serverless VPC Access and internal IP addresses.

Set up inbound connectivity from VPC to App Engine instances using an internal IP address

This scenario can be encountered when you want to connect to an App Engine instance using an internal (private) IP address. Serverless VPC Access is useful for making calls from Google's serverless offerings into the Virtual Private Cloud (VPC) network; however, it does not provide a way to access App Engine instances on internal IP addresses.

In this scenario, you can use one of the following options:

  • Set up Private Google Access, which allows VPC resources without external (or public) IP addresses to access the public IP addresses of the App Engine service.
  • Use Private Service Connect for Google APIs, which allows VPC resources to call App Engine using an internal IP address.

Virtual machines with only internal IP addresses require Private Google Access

Internal IP addresses are required when you deploy an App Engine flexible environment application in a Shared VPC network that adds a route to avoid

For instances with IP mode set to internal, you must make the following changes to the network:

  • Enable Private Google Access for each subnetwork that you use.
  • Create a route compatible with Private Google Access if it doesn't already exist.
  • Create a firewall rule compatible with Private Google Access if it doesn't already exist.
  • If you need outgoing internet access, you must also deploy Cloud NAT for each region attached to subnetworks that you use.

As documented in the internet access requirement for VPC networks, the network must have a valid default internet gateway route or custom route whose destination IP range is the most general ( If you remove this setting, it could cause deployment or serving failures.

Connect App Engine to Cloud SQL private IP addresses

This scenario may be encountered when you want to connect from App Engine standard environment or App Engine flexible environment apps to Cloud SQL instances over private IP addresses.

In this scenario, create a connection using one of the following options:

Troubleshoot a Cloud SQL instance using public IP addresses

When deploying an older App Engine standard environment app with Cloud SQL using Unix sockets, you might see a few error messages if your app is not correctly configured to connect to a Cloud SQL instance.

The following warning message indicates that App Engine was able to fall back on a legacy connection method to complete the operation successfully:

CloudSQL warning: your action is needed to update your application and avoid potential disruptions. Please see for additional details: ... 

The following error message indicates that the operation to connect to Cloud SQL was not completed successfully:

Cloud SQL connection failed. Please see for additional details: ...

For both error messages, you need to check the following to ensure that the Cloud SQL Auth proxy is correctly configured to connect to a Cloud SQL instance:

  • The Cloud SQL Admin API must be enabled.
  • The service account for the App Engine app must have the correct permissions.
  • The instance connection name must include the region.

If the failure message persists after troubleshooting, contact Google Cloud Support for assistance.

Customize access permissions between App Engine services

This scenario can be encountered when you have multiple App Engine services and want to configure access permissions differently between services (for example, you want to enable access to App Engine Service A only from App Engine Service B).

In this scenario, you can use App Engine with Identity-Aware Proxy (IAP) to make only some of the services publicly accessible while keeping others protected. To learn more, you can see the Centralize access to your organization's websites with IAP video and refer to the IAP documentation.

Inconsistent metrics when App Engine flexible environment uses Cloud Load Balancing

The App Engine flexible environment dashboard displays all metrics only for requests routed through a flexible environment managed backend. If you use App Engine flexible environment with Cloud Load Balancing, then certain metrics in the App Engine metrics table are reported as metrics from the loadbalancing table instead. For more information, see HTTP(S) Load Balancing logging and monitoring.