pg_pconnect not found

I am getting an error when postgre_driver.php tries to call pg_pconnect() (on line 153). Why would pg_pconnect not be found? I have copied the command from the php.net manual below. The correct dsn is being retrieved from database.php, btw. 

pg_pconnect
(PHP 4, PHP 5, PHP 7)
pg_pconnect — Open a persistent PostgreSQL connection
Description ¶
pg_pconnect ( string 

Code:

$connection_string

 [, int 

Code:

$connect_type

 ] ) : resource
pg_pconnect() opens a connection to a PostgreSQL database. It returns a connection resource that is needed by other PostgreSQL functions.

proof that an old dog can learn new tricks

solved it. Turns out that I needed to load pg driver inside the container.

proof that an old dog can learn new tricks