Postgresql: How to determine if database docker container running?

Question

On an docker image's entrypoint shell script I want to determine if a postgresql container can listen to connections. For mysql I used the following snippet:

while ! mysqladmin ping -h"$MOODLE_DB_HOST" -P $MOODLE_DB_PORT --silent; do
  echo "Connecting to ${MOODLE_DB_HOST} Failed"
  sleep 1
done

How can I achieve a similar using postgresql?

Solution

On the dockerfile add:

RUN apt-get update && apt-get install -f -y postgresql-client

Then on the entrypoint script use:

  while ! pg_isready -h ${MOODLE_DB_HOST} -p ${MOODLE_DB_PORT} > /dev/null 2> /dev/null; do
    echo "Connecting to ${MOODLE_DB_HOST} Failed"
    sleep 1
  done

Another approach

An another approach is by using netcat:

     for count in {1..100}; do
          echo "Pinging mysql database attempt "${count}
          if  $(nc -z ${DB_HOST} ${DB_PORT}) ; then
            echo "Can connect into database"
            break
          fi
          sleep 5
    done

Where variable ${DB_HOST} contains the database host whilst ${DB_PORT} contains the database port. Thas works on most databases (except if you want to detect its type as well where a custom script is needed).

Comments

[Diego Jancic]

I've tried the same on the Alpine image using apk add --no-cache postgresql-client and the pg_isready utility is not installed. Any ideas?

[Dimitrios Desyllas]

How about using netcat?

[Diego Jancic]

Thanks. I might end up using either this solution: stackoverflow.com/a/17309493/72350 or this one: github.com/vishnubob/wait-for-it that internally uses netcat. Both worked.

[Mark]

@diego-jancic, I just ran apk --update add postgresql-client on an Alpine image, and it installed the pg_isready utility successfully. Maybe this has changed since your comment, but, as of today, this seems to work.