Drupal 9

if (file_exists($app_root . '/' . $site_path . '/settings.local.php')) {
  include $app_root . '/' . $site_path . '/settings.local.php';
}

<?php
$databases['default']['default'] = array (
  'database' => 'tugboat',
  'username' => 'tugboat',
  'password' => 'tugboat',
  'prefix' => '',
  'host' => 'mysql',
  'port' => '3306',
  'namespace' => 'Drupal\\Core\\Database\\Driver\\mysql',
  'driver' => 'mysql',
);

// Use the TUGBOAT_REPO_ID to generate a hash salt for Tugboat sites.
$settings['hash_salt'] = hash('sha256', getenv('TUGBOAT_REPO_ID'));

// If your Drupal config directory is outside of the Drupal web root, it's
// recommended to uncomment and adapt the following. Note: the TUGBOAT_ROOT
// environment variable is equivalent to the git repo root.
# $settings['config_sync_directory'] = getenv('TUGBOAT_ROOT') . '/config';

// If you are using private files, and that directory is outside of the Drupal
// web root, it's recommended to uncomment and adapt the following. Note: the
// TUGBOAT_ROOT environment variable is equivalent to the git repo root.
# $settings['file_private_path'] = getenv('TUGBOAT_ROOT') . '/files-private';

services:
  # What to call the service hosting the site.
  php:
    # This uses PHP 8.1.x with Apache: update to match your version of PHP
    image: tugboatqa/php:8.1-apache

    # Set this as the default service. This does a few things
    #   1. Clones the git repository into the service container
    #   2. Exposes port 80 to the Tugboat HTTP proxy
    #   3. Routes requests to the preview URL to this service
    default: true

    # Wait until the mysql service is done building
    depends: mysql

    # A set of commands to run while building this service
    commands:
      # Commands that set up the basic preview infrastructure
      init:
        # Install opcache and mod-rewrite.
        - docker-php-ext-install opcache
        - a2enmod headers rewrite

        # Link the document root to the expected path. This example links /web
        # to the docroot.
        - ln -snf "${TUGBOAT_ROOT}/web" "${DOCROOT}"

        # Create the Drupal private and public files directories if they aren't
        # already present.
        - mkdir -p "${TUGBOAT_ROOT}/files-private" "${DOCROOT}/sites/default/files"

      # Commands that import files, databases,  or other assets. When an
      # existing preview is refreshed, the build workflow starts here,
      # skipping the init step, because the results of that step will
      # already be present.
      update:
        # Use the tugboat-specific Drupal settings.
        - cp "${TUGBOAT_ROOT}/.tugboat/settings.local.php" "${DOCROOT}/sites/default/"

        # Install/update packages managed by composer, including drush.
        - composer install --optimize-autoloader

        # Copy Drupal's public files directory from an external server. The
        # public SSH key found in the Tugboat Repository configuration must be
        # copied to the external server in order to use rsync over SSH.
        - rsync -av --delete user@example.com:/path/to/files/ "${DOCROOT}/sites/default/files/"

        # Alternatively, another common practice is to use the
        # stage_file_proxy Drupal module. This module lets Drupal serve
        # files from another publicly-accessible Drupal site instead of
        # syncing the entire files directory into the Tugboat Preview.
        # This results in smaller previews and reduces the build time.
        - composer require --dev drupal/stage_file_proxy
        - vendor/bin/drush pm:enable --yes stage_file_proxy
        - vendor/bin/drush config:set --yes stage_file_proxy.settings origin "http://www.example.com"

        # Set file permissions such that Drupal will not complain.
        - chgrp -R www-data "${DOCROOT}/sites/default/files"
        - find "${DOCROOT}/sites/default/files" -type d -exec chmod 2775 {} \;
        - find "${DOCROOT}/sites/default/files" -type f -exec chmod 0664 {} \;

      # Commands that build the site. This is where you would add things
      # like feature reverts or any other drush commands required to
      # set up or configure the site. When a preview is built from a
      # base preview, the build workflow starts here, skipping the init
      # and update steps, because the results of those are inherited
      # from the base preview.
      build:
        - composer install --optimize-autoloader
        - vendor/bin/drush cache:rebuild
        - vendor/bin/drush config:import -y
        - vendor/bin/drush updatedb -y
        - vendor/bin/drush cache:rebuild

  # This 'mysql' key acts as the hostname to access the service by from the php service.
  mysql:
    # Use the latest available 5.x version of MySQL
    image: tugboatqa/mariadb:10.5

    # A set of commands to run while building this service
    commands:
      # Commands that import files, databases,  or other assets. When an
      # existing preview is refreshed, the build workflow starts here,
      # skipping the init step, because the results of that step will
      # already be present.
      update:
        # Copy a database dump from an external server. The public
        # SSH key found in the Tugboat Repository configuration must be
        # copied to the external server in order to use scp.
        - scp user@example.com:database.sql.gz /tmp/database.sql.gz
        - zcat /tmp/database.sql.gz | mysql tugboat
        - rm /tmp/database.sql.gz