I tried to follow the steps in: https://cloud.google.com/sql/docs/mysql/connect-kubernetes-engine.

I have the application container and the cloudsql proxy container running in the same pod.

After creating the cluster, logs for the proxy container seems correct:

$kubectl logs users-app-HASH1-HASH2 cloudsql-proxy
2018/08/03 18:58:45 using credential file for authentication; email=it-test@tutorial-bookshelf-xxxxxx.iam.gserviceaccount.com
2018/08/03 18:58:45 Listening on 127.0.0.1:3306 for tutorial-bookshelf-xxxxxx:asia-south1:it-sample-01
2018/08/03 18:58:45 Ready for new connections

However logs from the application container throws up an unable to connect on localhost error:

$kubectl logs users-app-HASH1-HASH2 app-container
...
19:27:38 users_app.1 |     return Connection(*args, **kwargs)
19:27:38 users_app.1 |   File "/usr/local/lib/python3.7/site-packages/pymysql/connections.py", line 327, in __init__
19:27:38 users_app.1 |     self.connect()
19:27:38 users_app.1 |   File "/usr/local/lib/python3.7/site-packages/pymysql/connections.py", line 629, in connect
19:27:38 users_app.1 |     raise exc
19:27:38 users_app.1 | sqlalchemy.exc.OperationalError: (pymysql.err.OperationalError) (2003, "Can't connect to MySQL server on 'localhost' ([Errno 2] No such file or directory)") (Background on this error at: http://sqlalche.me/e/e3q8)

The SQLALCHEMY_DATABASE_URI is 'mysql+pymysql://{user}:{password}@/{database}?unix_socket=/cloudsql/{cloudsql_connection_name}' and is populated with the correct values (credentials that I set using kubectl secrets).

I'm sure I'm doing something silly here, so I'm hoping someone more experience on GCP could take a look and provide pointers on troubleshooting this issue.

UPDATE: I just went to the GCP kubernetes engine page and opened up a shell on the app container and tried to connect to the cloud sql instance. That seemed to have worked.

$gcloud container cluster ......... -it /bin/sh
#python
>>> import pymysql
>>> connection = pymysql.connect(host='127.0.0.1', user='user', password='password', db='db')
>>> with connection.cursor() as cursor:
...     cursor.execute("show databases;")
...     tables = cursor.fetchall()
...
5

But the following (when I try and connect through sqlalchemy) fails:

>>> connection = pymysql.connect(host='127.0.0.1', user='u', password='p', db='d', unix_socket='/cloudsql/CONNECTION_NAME')
...
pymysql.err.OperationalError: (2003, "Can't connect to MySQL server on '127.0.0.1' ([Errno 2] No such file or directory)")




>>> from sqlalchemy import create_engine

>>> engine = create_engine('mysql://user:password@localhost/db')
>>> engine.connect()
Traceback (most recent call last):
    ...    
sqlalchemy.exc.OperationalError: (_mysql_exceptions.OperationalError) (2002, 'Can\'t connect to local MySQL server through socket \'/run/mysqld/mysqld.sock\' (2 "No such file or directory")') (Background on this error at: http://sqlalche.me/e/e3q8)




>>> engine = create_engine('mysql+pymysql://user:password@/db?unix_socket=/cloudsql/tutorial-bookshelf-xxxx:asia-south1:test-01')
>>> engine.connect()
Traceback (most recent call last):
    ...
    raise exc
sqlalchemy.exc.OperationalError: (pymysql.err.OperationalError) (2003, "Can't connect to MySQL server on 'localhost' ([Errno 2] No such file or directory)") (Background on this error at: http://sqlalche.me/e/e3q8)