wait_db

The main purpose of this project is to be able to wait for a database (for now, MySQL) running inside a container to be ready for connections after startup. All approaches I found rely on a script that tries over and over to connect to the database, or try to establish a TCP connection with the container. My approach in this script is to rely on the retrieved log from the container.

How it works

The script will follow the log waiting for a specific string that represents the server is ready for connections. When the script finds the string then it will finish.

Using the script

The script can be found on wait_db.sh and be used as follows:

wait_db [CONTAINER TYPE] [OPTIONS]

It can be way easier to see the examples below.

Example 01: Using with Docker Compose

SERVICE_NAME="mysql" && \
docker-compose up -d $SERVICE_NAME && \
./wait_db.sh docker-compose --no-color $SERVICE_NAME

Example 02: Using with Docker

CONTAINER_NAME="wait-db-test" && \
ISO_NOW=$(date -uIs) && \
  docker run --rm --name $CONTAINER_NAME \
    -e MYSQL_ROOT_PASSWORD=$ROOT_PASSWORD \
    -d mysql:5.7 && \
./wait_db.sh docker --since "$ISO_NOW" $CONTAINER_NAME

Testing

A complete test can be found on the test_wait_db.sh file. Just put the two files (test_wait_db.sh and wait_db.sh) in a empty folder and then execute:

./test_wait_db.sh

Technical

About the script, I'd like to register the reason I used the double grep. It seems like the function follow of docker (and docker-compose) does not exit normally when there is no new output from log. This way, the script can continue normally and, the follow command will finish as soon as a new entry to the console appears.

Contributions

The script was made by me (Marcelo Barros). I hope it can helps anyone. It can be shared and modified as you want. If it's useful for you, the only thing I ask is to refer to this repository, so I can improve my code. Thanks!