title: Docker updating image along when dockerfile changes
body: <p>I'm playing with docker by creating a <code>Dockerfile</code> with some nodejs instructions. Right now, every time I make changes to the dockerfile I recreate the image by running <code>sudo docker build -t nodejstest .</code> in my project folder however, this creates a new image each time and swallows my ssd pretty soon.</p>
  
  <p>Is there a way I can update an existing image when I change the dockerfile or I'm forced to create a new one each time I make changes to the file?</p>
  
  <p>Sorry if it's a dumb question</p>