September 20, 2016

How do I know when my docker mysql container is up and mysql is ready for taking queries?

Haren’s Question:

I am deploying a few different docker containers, mysql being the first one. I want to run scripts as soon as database is up and proceed to building other containers. The script has been failing because it was trying to run when the entrypoint script, which sets up mysql (from this official mysql container), was still running.


sudo docker run --name mysql -e MYSQL_ROOT_PASSWORD=MY_ROOT_PASS -p 3306:3306 -d mysql
[..] wait for mysql to be ready [..]
mysql -h 127.0.0.1 -P 3306 -u root --password=MY_ROOT_PASS < MY_SQL_SCRIPT.sql

Is there a way to wait for a signal of an entrypoiny mysql setup script finishing inside the docker container? Bash sleep seems like a suboptimal solution.

EDIT: Went for a bash script like this. Not the most elegant and kinda brute force but works like a charm. Maybe someone will find that useful.


OUTPUT="Can't connect"
while [[ $OUTPUT == *"Can't connect"* ]]
do
OUTPUT=$(mysql -h $APP_IP -P :$APP_PORT -u yyy --password=xxx < ./my_script.sql 2>&1)
done

On your ENTRYPOINT script, you have to check if you have a valid MySQL connection or not.

This solution does not require you to install a MySQL Client on the container and while running the container with php:7.0-fpm running nc was not an option, because it had to be installed as well. Also, checking if the port is open does not necessarily mean that the service is running and exposed correctly. [more of this]

So in this solution, I will show you how to run a PHP script to check if a MySQL Container is able to take connection. If you want to know why I think this is a better approach check my comment here.

File entrypoint.sh

#!/bin/bash
cat << EOF > /tmp/wait_for_mysql.php
<?php
$connected = false;
while(!$connected) {
    try{
        $dbh = new pdo( 
            'mysql:host=mysql:3306;dbname=db_name', 'db_user', 'db_pass',
            array(PDO::ATTR_ERRMODE => PDO::ERRMODE_EXCEPTION)
        );
        $connected = true;
    }
    catch(PDOException $ex){
        error_log("Could not connect to MySQL");
        error_log($ex->getMessage());
        error_log("Waiting for MySQL Connection.");
        sleep(5);
    }
}
EOF
php /tmp/wait_for_mysql.php
# Rest of entry point bootstrapping

By running this, you are essentially blocking any bootstrapping logic of your container UNTIL you have a valid MySQL Connection.

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