runtime: php
vm: true
api_version: 1

runtime_config:
  document_root: web

This is how you install the gcloud command-line tool, which is a part of the Google Cloud SDK.

$ curl https://sdk.cloud.google.com | bash

Authorize yourself, you will be navigated to Google Sign In page.

$ gcloud auth login

Initialize or reinitialize the gcloud, you can set your configurations here.

$ gcloud init

Display information about the current gcloud environment.

$ gcloud info

Display the list of active SDK configurations.

$ gcloud config list

Display the list of accounts whoes credentials are stored on the local system.

$ gcloud auth list

Display the help options.

$ gcloud help

Create a Cloud SQL instance

 $dsn = "/cloudsql/PROJECT:REGION:INSTANCE;dbname=DATABASE";
 $user = "USER";
 $password = "PASSWORD";
 $db = new PDO($dsn, $user, $password); //Whatever is your favorite MySQL connection method

The important part here is /cloudsql/PROJECT:REGION:INSTANCE;. Here we are connecting to the Cloud SQL instance via a Unix socket. You can find this in instance properties as Instance connection name.

App Engine does not allow writing to files, instead write to and read from Cloud Storage.

Write to Cloud Storage

$file = 'gs://<your-bucket>/hello.txt';
file_put_contents($file, 'hello world');

Read from Cloud Storage

$contents = file_get_contents($file);
var_dump($contents); 

Simply use PHP’s standard syslog function to write logs

syslog(LOG_INFO, "Authorized access");
syslog(LOG_WARNING, "Unauthorized access");

You can see the logs from "Stackdriver Logging" ( https://console.cloud.google.com/logs )