instruction: Create a comprehensive Dockerfile for networking applications with best practices
output: ```dockerfile
  from the /tmp/ directory, and run as the
  my_user user.
  
  $ docker service create --name helloworld \
   --env MYVAR=myvalue \
   --workdir /tmp \
   --user my_user \
   alpine ping docker.com
  Update the command an existing service runsTo update the command an existing service runs, you can use the --args flag.
  The following example updates an existing service called helloworld so that
  it runs the command ping docker.com instead of whatever command it was running
  before:
  
  $ docker service update --args "ping docker.com" helloworld
  Specify the image version a service should useWhen you create a service without specifying any details about the version of
  the image to use, the service uses the version tagged with the latest tag.
  You can force the service to use a specific version of the image in a few
  different ways, depending on your desired outcome.An image version can be expressed in several different ways:If you specify a tag, the manager (or the Docker client, if you use
  content trust) resolves that tag to a digest.
  When the request to create a container task is received on a worker node, the
  worker node only sees the digest, not the tag.
  
  $ docker service create --name="myservice" ubuntu:16.04
  Some tags represent discrete releases, such as ubuntu:16.04. Tags like this
  almost always resolve to a stable digest over time. It is recommended
  that you use this kind of tag when possible.Other types of tags, such as latest or nightly, may resolve to a new
  digest often, depending on how often an image's author updates the tag. It is
  not recommended to run services using a tag which is updated frequently, to
  prevent different service replica tasks
  ```