Spring Boot application in Google App Engine can't connect to Cloud SQL

As documented here:

App Engine standard enviroments do not support connecting to the Cloud SQL instance using TCP. Your code should not try to access the instance using an IP address (such as 127.0.0.1 or 172.17.0.1) unless you have configured Serverless VPC Access.

First, you'll need to remove the beta_settings entry in your app.yaml file since:

• it is intended for App Engine Flexible (and actually instruct the platform to spin up a sidecar container running the CloudSQL proxy, which you don't need with Socket Factory for JDBC)
• the syntax you used with =tcp:5432 would actually instructs the CloudSQL proxy to connect via TCP port.

So your Base JDBC url should look like jdbc:postgresql://google/recruiters_wtf

Your full datasource url would be (note the removed =tcp:5432 part):

jdbc:postgresql://google/recruiters_wtf?cloudSqlInstance=recruiters-wtf:europe-west2:recruiters-wtf&socketFactory=com.google.cloud.sql.postgres.SocketFactory&user=${DB_USER}&password=${DB_PASS}

Finally, note that, as mentioned in the link I provided above:

The PostgreSQL standard requires the Unix socket to have a .s.PGSQL.5432 suffix in the socket path. Some libraries apply this suffix automatically, but others require you to specify the socket path as follows: /cloudsql/INSTANCE_CONNECTION_NAME/.s.PGSQL.5432.