title: Can I set/get variables in docker-compose.yml files?
body: <p>I want to have a variable in a <code>docker-compose.yml</code> for my project that represents a port and instead of putting <code>8080</code> everywhere in the file, I'd rather use it as a variable.</p>
  
  <p>Is it possible to set variable, say in the beginning of the file, then reuse it in other places of the file?</p>