simple docker entrypoint for rails project - check if database is up, from $DATABASE_URL which contains both port and hostname.

docker-entrypoint

#!/bin/bash

set -e

# Extract hostname and port from DATABASE_URL
DB_HOST=$(echo $DATABASE_URL | sed -n 's/^.*[^@]*@\([^:]*\):[0-9]*.*$/\1/p')
DB_PORT=$(echo $DATABASE_URL | sed -n 's/^.*[^@]*@[^\:]*:\([0-9]*\).*$/\1/p')

# Wait for the database to be ready before starting the application
until nc -z -v -w30 $DB_HOST $DB_PORT; do
  echo "Waiting for database connection..."
  sleep 1
done
echo "Database is ready!"

# If running the rails server then create or migrate existing database
if [ "${1}" == "./bin/rails" ] && [ "${2}" == "server" ]; then
  ./bin/rails db:prepare
fi

exec "${@}"