instruction: Create a Dockerfile for orchestration
output: ```dockerfile
  from the convenience of your development machine.Describe apps using stack filesSwarm never creates individual containers like you did in the previous step of this tutorial. Instead, all Swarm workloads are scheduled as services, which are scalable groups of containers with added networking features maintained automatically by Swarm. Furthermore, all Swarm objects can and should be described in manifests called stack files. These YAML files describe all the components and configurations of your Swarm app, and can be used to create and destroy your app in any Swarm environment.Now you can write a simple stack file to run and manage your Todo app, the container getting-started image created in Part 2 of the tutorial. Place the following in a file called bb-stack.yaml:
  NoteThe docker stack deploy command uses the legacy
  Compose file version 3
  format, used by Compose V1. The latest format, defined by the
  Compose specification
  isn't compatible with the docker stack deploy command.For more information about the evolution of Compose, see
  History of Compose.
  
  version: "3.7"
  
  services:
   bb-app:
   image: getting-started
   ports:
   - "8000:3000"In this Swarm YAML file, there is one object, a service, describing a scalable group of identical containers. In this case, you'll get just one container (the default), and that container will be based on your getting-started image created in Part 2 of the tutorial. In addition, you've asked Swarm to forward all traffic arriving at port 8000 on your development machine to port 3000 inside our getting-started container.Kubernetes Services and Swarm Services are very differentDespite the similar name, the two orchestrators mean very different things by
  the term 'service'. In Swarm, a service provides both scheduling and
  networking facilities, creating containers and providing tools for routing
  traffic to them. In Kubernetes, scheduling and networking are handled
  separately, deployments (or other controllers) handle the scheduling of
  containers as pods, while services are responsible only for adding
  networking features to those pods.Deploy and check your applicationDeploy your application to Swarm:
  
  $ docker stack deploy -c bb-stack.yaml demo
  If all goes well, Swarm will report creating all your stack objects with no complaints:
  
  Creating network demo_default
  Creating service demo_bb-appNotice that in addition to your service, Swarm also creates a Docker network by default to isolate the containers deployed as part of your stack.Make sure everything worked by listing your service:
  
  $ docker service ls
  If all has gone well, your service will report with 1/1 of its replicas created:
  
  ID NAME MODE REPLICAS IMAGE PORTS
  il7elwunymbs demo_bb-app replicated 1/1 getting-started:latest *:8000->3000/tcpThis indicates 1/1 containers you asked for as part of your services are up and running. Also, you see that port 8000 on your development machine is getting forwarded to port 3000 in your getting-started container.Open a browser and visit your Todo app at localhost:8000; you should see your Todo application, the same as when you ran it as a stand-alone container in Part 2 of the tutorial.Once satisfied, tear down your application:
  
  $ docker stack rm demo
  ConclusionAt this point, you've successfully used Docker Desktop to deploy your application to a fully-featured Swarm environment on your development machine. You can now add other components to your app and taking advantage of all the features and power of Swarm, right on your own machine.In addition to deploying to Swarm, you've also described your application as a stack file. This simple text file contains everything you need to create your application in a running state; you can check it in to version control and share it with your colleagues, letting you to distribute your applications to other clusters (like the testing and production clusters that probably come after your development environments).Swarm and CLI referencesFurther documentation for all new Swarm objects and CLI commands used in this article are available here:Swarm ModeSwarm Mode ServicesSwarm Stacksdocker stack *docker service *
  Request changesTable of contentsPrerequisitesIntroductionDescribe apps using stack filesDeploy and check your applicationConclusionSwarm and CLI references
  
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