psycopg2.OperationalError: FATAL: unsupported frontend protocol 1234.5679: server supports 2.0 to 3.0

Question

I\'m using Macbook

Psycopg2 works well when connecting the localhost db (PostgreSQL on Mac). The error was raised when I tried to connect PostgreSQL db on a Windows1

Answer 1

In order to have a SSL connection working and using certificates, you can disable GSS connection mode to avoid the client to attempt to connect with GSS and directly try a SSL connection (Postgres version 12 < 12.3, I had no such issues with a test on version 11).

Below an example with the verify-ca option, providing filenames for certificates and key (example names from GCP Cloud SQL, running Postgres 12.1 when posted).

   from sqlalchemy import create_engine

   db_user = 'user'
   db_pwd = 'secret'
   db_host = 'hostname'
   db_port = '5432'
   db_name = 'test'

   cnn = f'postgresql://{db_user}:{db_pwd}@{db_host}:{db_port}/{db_name}'
   ssl_args = {
       'gssencmode': 'disable',
       'sslmode': 'verify-ca',
       'sslrootcert': 'server-ca.pem',
       'sslcert': 'client-cert.pem',
       'sslkey': 'client-key.pem',
   }
   
   engine = create_engine(cnn, connect_args=ssl_args)

This engine can then be used with pandas for example:

   df.to_sql('my_table', con=engine)