How do I know when my docker mysql container is up

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

Answer 1

If the docker container waiting for a mysql container is based on a python image (for instance for a Django application), you can use the code below.

Advantages are:

• It's not based on wait-for-it.sh, which does wait for the IP and port of mysql to be ready, but this doesn't automatically mean also that the mysql initialization has finished.
• It's not a shell script based on a mysql or mysqladmin executable that must be present in your container: since your container is based on a python image, this would require installing mysql on top of that image. With the below solution, you use the technology that is already present in the container: pure python.

Code:

import time

import pymysql


def database_not_ready_yet(error, checking_interval_seconds):
    print('Database initialization has not yet finished. Retrying over {0} second(s). The encountered error was: {1}.'
          .format(checking_interval_seconds,
                  repr(error)))
    time.sleep(checking_interval_seconds)


def wait_for_database(host, port, db, user, password, checking_interval_seconds):
    """
    Wait until the database is ready to handle connections.

    This is necessary to ensure that the application docker container
    only starts working after the MySQL database container has finished initializing.

    More info: https://docs.docker.com/compose/startup-order/ and https://docs.docker.com/compose/compose-file/#depends_on .
    """
    print('Waiting until the database is ready to handle connections....')
    database_ready = False
    while not database_ready:
        db_connection = None
        try:
            db_connection = pymysql.connect(host=host,
                                            port=port,
                                            db=db,
                                            user=user,
                                            password=password,
                                            charset='utf8mb4',
                                            connect_timeout=5)
            print('Database connection made.')
            db_connection.ping()
            print('Database ping successful.')
            database_ready = True
            print('The database is ready for handling incoming connections.')
        except pymysql.err.OperationalError as err:
            database_not_ready_yet(err, checking_interval_seconds)
        except pymysql.err.MySQLError as err:
            database_not_ready_yet(err, checking_interval_seconds)
        except Exception as err:
            database_not_ready_yet(err, checking_interval_seconds)
        finally:
            if db_connection is not None and db_connection.open:
                db_connection.close()

Usage:

1. Add this code into a python file (wait-for-mysql-db.py for instance) inside your application's source code.
2. Write another python script (startup.py for instance) that first executes the above code, and afterwards starts up your application.
3. Make sure your application container's Dockerfile packs these two python scripts together with the application's source code into a Docker image.
4. In your docker-compose file, configure your application container with: command: ["python3", "startup.py"].

Note that this solution is made for a MySQL database. You'll need to adapt it slightly for another database.

Answer 2

I had the same issue when my Django container tried to connect the mysql container just after it started. I solved it using the vishnubob's wait-for.it.sh script. Its a shell script which waits for an IP and a host to be ready before continuing. Here is the example I use for my applicaction.

./wait-for-it.sh \
    -h $(docker inspect --format '{{ .NetworkSettings.IPAddress }}' $MYSQL_CONTAINER_NAME) \
    -p 3306 \
    -t 90

In that script I'm asking to the mysql container to wait maximum 90 seconds (it will run normally when ready) in the port 3306 (default mysql port) and the host asigned by docker for my MYSQL_CONTAINER_NAME. The script have more variables but for mw worked with these three.

Answer 3

I use the following code ;

export COMPOSE_PROJECT_NAME=web;

export IS_DATA_CONTAINER_EXISTS=$(docker volume ls | grep ${COMPOSE_PROJECT_NAME}_sqldata);

docker-compose up -d;
docker-compose ps;

export NETWORK_GATEWAY=$(docker inspect --format='{{range .NetworkSettings.Networks}}{{.Gateway}}{{end}}' ${COMPOSE_PROJECT_NAME}_webserver1_con);

Answer 4

You can install mysql-client package and use mysqladmin to ping target server. Useful when working with multiple docker container. Combine with sleep and create a simple wait-loop:

while ! mysqladmin ping -h"$DB_HOST" --silent; do
    sleep 1
done

Answer 5

Some times the problem with the port is that the port could be open, but the database is not ready yet.

Other solutions require that you have installed the mysql o a mysql client in your host machine, but really you already have it inside the Docker container, so I prefer to use something like this:

while ! docker exec mysql mysqladmin --user=root --password=root --host "127.0.0.1" ping --silent &> /dev/null ; do
    echo "Waiting for database connection..."
    sleep 2
done

Answer 6

I've found that using the mysqladmin ping approach isn't always reliable, especially if you're bringing up a new DB. In that case, even if you're able to ping the server, you might be unable to connect if the user/privilege tables are still being initialized. Instead I do something like the following:

while ! docker exec db-container mysql --user=foo --password=bar -e "SELECT 1" >/dev/null 2>&1; do
    sleep 1
done

So far I haven't encountered any problems with this method. I see that something similar was suggested by VinGarcia in a comment to one of the mysqladmin ping answers.