An App Engine standard app returns 502 because it cannot connect to Memorystore for Redis. Which explanation fits this failure?

The correct answer is that you configured your Serverless VPC Access connector in a different region than your App Engine instance. Serverless VPC Access connectors must be in the same region as the serverless environment (like App Engine) they are connecting from. If the connector is in a different region, App Engine cannot use it to establish a private connection to resources within your VPC network, such as Memorystore for Redis, leading to connection failures and 502 errors. Incorrect options: Memorystore for Redis instances are typically accessed via private IP addresses within a VPC network, not public IPs, so this is not the primary issue. While firewall rules are important, the most common cause of regional connection issues with Serverless VPC Access is a regional mismatch. Serverless VPC Access connectors can operate across different subnets and availability zones within the same region without issue, as long as the region matches the App Engine instance.