title: how to edit blueprint for automatically running a command in docker container run by cloudify
body: <p>I want to run a docker container of RYU controller in cloudify ways. I have written a blueprint file with which I can create relevant deployment and finally start the docker container. </p>
  
  <p>The problem is, the controller (within the docker container) needs to implement a script to function but I don't know how to modify the blueprint file for automatically running the script. Every time, I have to type <code>docker exec CONTAINER ryu-manager /path/simple_switch.py</code> for the goal.</p>
  
  <p>So does anyone know where the command should be put in the blueprint. I tried to include it in </p>
  
  <pre><code>interfaces:
    cloudify.interfaces.lifecycle:
      create:
        implementation: docker.docker_plugin.tasks.create_container
        inputs:
          params:
            ports:
              - { get_input: docker_port }
            stdin_open: true
            tty: true
            command: /bin/bash
  
      start:
        implementation: docker.docker_plugin.tasks.start
        inputs:
          params:
            port_bindings: { get_input: container_port_binding }
            command: docker exec ryu ryu-manager /ryu/ryu/app/simple_switch.py
            # here ↑ ↑ ↑ ↑ ↑ ↑ ↑ ↑ ↑ ↑ ↑ ↑ ↑ ↑ ↑ ↑ ↑ ↑ ↑ ↑ ↑ ↑ ↑ ↑ ↑ ↑ ↑ ↑ ↑ ↑ 
  </code></pre>
  
  <p>but received an error of unexpected parameter.</p>
  
  <p>Thanks for your time and any opinions would be appreciated~</p>
  
  <hr>
  
  <p>Or let me put in this way, if anyone knows, which part in the cloudify blueprint matches <code>docker exec</code>?</p>