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up vote 0 down vote favorite

I wonder if there is an alternative to the psql command to test the connection to a postgresql database using bash.

I'm setting up a Core OS cluster and have a side service which should perform the equivalent of psql 'host=xxx port=xxx dbname=xxx user=xxx' every minute to determine if the service is running, and more important, if one can connect to it using the given parameters).

I cannot install postgres directly on Core OS. The command usually used in Core OS is something like curl -f ${COREOS_PUBLIC_IPV4}:%i;. But it tells only if the service itself is running on the given port, without any access check.

Thank you in advance!

share|improve this question
    
I cannot install postgres directly on Core OS: so what can you install? – Daniel Vérité Nov 13 '14 at 18:47
    
Docker containers... so basically the options seem 1. do the job in bash or 2. run a container (which is quite suboptimal for checking the availability of other units) – Raphael Nov 14 '14 at 9:49
up vote 1 down vote

You can build a simple container that extends the first (to conserve disk) to perform the check. For example:

FROM postgres

ENTRYPOINT [ "psql", "-h", "$POSTGRES_PORT_5432_TCP_ADDR",  "-p", "$POSTGRES_PORT_5432_TCP_PORT" ]

If you're using a different image than postgres, of course use that one. You can use pretty much any command line you like and still check exit codes from bash on the CoreOS host:

#!/bin/sh
if ! docker run --link postgres:postgres psql --command "select * from foo;" ; then
   # Do something
fi
share|improve this answer
up vote 0 down vote

you can write a simple connection script in your language of choice.

hopefully your Core OS system has one of perl, php, python, ruby, etc installed

here is one in python:

#!/usr/bin/python2.4
#
import psycopg2
try:
    db = psycopg2.connect("dbname='...' user='...' host='...' password='...'")
except:
    exit(1)

exit(0)

now your cmdline looks like this

python psqltest.py && echo 'OK' || echo 'FAIL'
share|improve this answer
    
Thank you David. Unfortunately, none of these language is installed on CoreOs (which is readonly...) – Raphael Nov 13 '14 at 16:47

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