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To restore a backup from the same instance:

gcloud sql backups restore [BACKUP_ID] --restore-instance=[INSTANCE_NAME]

To restore a backup from a different instance:

gcloud sql backups restore [BACKUP_ID] --restore-instance=[TARGET_INSTANCE_NAME] \
                                      --backup-instance=[SOURCE_INSTANCE_NAME]

Before you do the above, make sure to run:

gcloud sql backups list --instance [INSTANCE_NAME]

find the backup you want to use, record its ID value, and select a backup that is marked 'SUCCESSFUL'

Here is the complete documentation about Restoring an Instance.

The order of your URL handlers is not correct.

GAE does these top to bottom. Your first handler will match everything. It will never reach the other two.

You'll need to change the order in your app.yaml:

threadsafe: true
runtime: php55
api_version: 2

handlers:

# The root URL (/) is handled by the Go application.
# No other URLs match this pattern.

- url: /
  static_files: index.html
  upload: index.html

- url: /web-service/*
  script: web-service/yii

- url: /(.+)
  static_files: \1
  upload: (.*)

Suggested is to always have the broadest on the bottom, and the strictest on top.

See the section for it in the GAE app.yaml documentation.