title: Docker placement preference vs Docker placement constraints
body: <p>I am learning Docker. As part of my learning there is one topic I haven't understood. The usage of the Docker placement preferences when compared with constraints in Docker.</p>
  
  <p>I have been keep searching in internet and asked many people everyone aware of the constraints not the preferences. I haven't found any good reference in internet. What is the use of placement preferences in Docker? When should I use them? Any sample example?</p>