Example spinning up containers from containers using Docker Engine API and PHP.

docker-manager.php

<?php

class DockerManager {

  /**
   * This is where the magic happens.
   * The Docker Engine socket needs to be mounted in docker-compose.yml.
   *
   *    volumes:
   *      - /var/run/docker.sock:/var/run/docker.sock
   *
   */
  const DOCKER_SOCKET = '/var/run/docker.sock';

  /**
   * This is the working directory for the new container.
   */
  const WORKING_DIR = '/app/processing';

  /**
   *  Setup the defaults for working with Docker Engine API via curl.
   */
  private function curl_prepare( &$ch, $method = 'POST' ) {

    // Here we setup our docker socket. (New to PHP 7)
    curl_setopt( $ch, CURLOPT_UNIX_SOCKET_PATH, static::DOCKER_SOCKET );

    curl_setopt( $ch, CURLOPT_HTTPHEADER,array( 'Content-Type: application/json' ) );

    if ( 'POST' === $method ) {
      curl_setopt( $ch, CURLOPT_POST, 1 );
    }

    // Return the results of the curl operation as a response.
    curl_setopt( $ch, CURLOPT_RETURNTRANSFER, 1 );
  }

  /**
   * This sets up the container, but does not yet start it.
   *
   * @return string The container ID.
   */
  public function create_container( $args = array() ) {

    $ch = curl_init();
    $this->curl_prepare($ch);

    curl_setopt( $ch, CURLOPT_URL, 'http:/v1.26/containers/create' );

    /**
     * The POST request variables.
     *
     * @see https://docs.docker.com/engine/api/v1.26/#operation/ContainerCreate
     */
    $data = array_merge( array(
      'Image' => 'php:alpine',
      'HostConfig' => array(
        'VolumesFrom' => array( getenv('HOSTNAME') . ':rw' ),
      ),
      'WorkingDir' => static::WORKING_DIR,
    ), $args );


    curl_setopt( $ch, CURLOPT_POSTFIELDS, json_encode( $data ) );

    try {
      $response = json_decode( curl_exec($ch) );
      $response = $response->Id;
    } catch (Exception $e) {
      $response = false;
    }

    curl_close($ch);

    return $response;
  }

  public function start_container( $container_id ) {

    if ( false === $container_id ) {
      echo "No ID: Could not start the container\n";
    }

    $ch = curl_init();
    $this->curl_prepare($ch);
    curl_setopt( $ch, CURLOPT_URL, 'http:/v1.26/containers/' . $container_id . '/start' );

    try {
      $response = json_decode( curl_exec($ch) );
      echo sprintf( "Started container: %s\n", $container_id );
    } catch (Exception $e) {
      echo "Unexpected Error: Could not start the container.\n";
      print_r( $e );
    }

    curl_close($ch);
  }

}

/**
 * Example: Creating and starting a new container via Docker Engine API.
 */
$docker_manager = new DockerManager();

$container_id = $docker_manager->create_container( array(
  'Cmd' => array( 'php', 'processing.php', 'CLI Argument' ),
  'Env' => array(
    'API_KEY=' . uniqid(), // Has to be string key=value pair
   ),
) );
$docker_manager->start_container( $container_id );

thanks !
But how Run a command inside a running container?