--- description: How to deploy a stack to a swarm keywords: guide, swarm mode, composefile, stack, compose, deploy title: Deploy a stack to a swarm --- When running Docker Engine in swarm mode, you can use `docker stack deploy` to deploy a complete application stack to the swarm. The `deploy` command accepts a stack description in the form of a [Compose file](../../compose/compose-file/compose-file-v3.md). {% include swarm-compose-compat.md %} The `docker stack deploy` command supports any Compose file of version "3.x". If you have an older version, see the [upgrade guide](../../compose/compose-file/compose-versioning.md#upgrading). To run through this tutorial, you need: 1. A Docker Engine running in [swarm mode](swarm-mode.md). If you're not familiar with swarm mode, you might want to read [Swarm mode key concepts](key-concepts.md) and [How services work](how-swarm-mode-works/services.md). > **Note** > > If you're trying things out on a local development environment, > you can put your engine into swarm mode with `docker swarm init`. > > If you've already got a multi-node swarm running, keep in mind that all > `docker stack` and `docker service` commands must be run from a manager > node. 2. A current version of [Docker Compose](../../compose/install/index.md). ## Set up a Docker registry Because a swarm consists of multiple Docker Engines, a registry is required to distribute images to all of them. You can use the [Docker Hub](https://hub.docker.com) or maintain your own. Here's how to create a throwaway registry, which you can discard afterward. 1. Start the registry as a service on your swarm: ```console $ docker service create --name registry --publish published=5000,target=5000 registry:2 ``` 2. Check its status with `docker service ls`: ```console $ docker service ls ID NAME REPLICAS IMAGE COMMAND l7791tpuwkco registry 1/1 registry:2@sha256:1152291c7f93a4ea2ddc95e46d142c31e743b6dd70e194af9e6ebe530f782c17 ``` Once it reads `1/1` under `REPLICAS`, it's running. If it reads `0/1`, it's probably still pulling the image. 3. Check that it's working with `curl`: ```console $ curl http://localhost:5000/v2/ {} ``` ## Create the example application The app used in this guide is based on the hit counter app in the [Get started with Docker Compose](../../compose/gettingstarted.md) guide. It consists of a Python app which maintains a counter in a Redis instance and increments the counter whenever you visit it. 1. Create a directory for the project: ```console $ mkdir stackdemo $ cd stackdemo ``` 2. Create a file called `app.py` in the project directory and paste this in: ```python from flask import Flask from redis import Redis app = Flask(__name__) redis = Redis(host='redis', port=6379) @app.route('/') def hello(): count = redis.incr('hits') return 'Hello World! I have been seen {} times.\n'.format(count) if __name__ == "__main__": app.run(host="0.0.0.0", port=8000, debug=True) ``` 3. Create a file called `requirements.txt` and paste these two lines in: ```none flask redis ``` 4. Create a file called `Dockerfile` and paste this in: ```dockerfile # syntax=docker/dockerfile:1 FROM python:3.4-alpine ADD . /code WORKDIR /code RUN pip install -r requirements.txt CMD ["python", "app.py"] ``` 5. Create a file called `docker-compose.yml` and paste this in: ```none services: web: image: 127.0.0.1:5000/stackdemo build: . ports: - "8000:8000" redis: image: redis:alpine ``` The image for the web app is built using the Dockerfile defined above. It's also tagged with `127.0.0.1:5000` - the address of the registry created earlier. This is important when distributing the app to the swarm. ## Test the app with Compose 1. Start the app with `docker compose up`. This builds the web app image, pulls the Redis image if you don't already have it, and creates two containers. You see a warning about the Engine being in swarm mode. This is because Compose doesn't take advantage of swarm mode, and deploys everything to a single node. You can safely ignore this. ```none $ docker compose up -d WARNING: The Docker Engine you're using is running in swarm mode. Compose does not use swarm mode to deploy services to multiple nodes in a swarm. All containers are scheduled on the current node. To deploy your application across the swarm, use `docker stack deploy`. Creating network "stackdemo_default" with the default driver Building web ...(build output)... Creating stackdemo_redis_1 Creating stackdemo_web_1 ``` 2. Check that the app is running with `docker compose ps`: ```console $ docker compose ps Name Command State Ports ----------------------------------------------------------------------------------- stackdemo_redis_1 docker-entrypoint.sh redis ... Up 6379/tcp stackdemo_web_1 python app.py Up 0.0.0.0:8000->8000/tcp ``` You can test the app with `curl`: ```console $ curl http://localhost:8000 Hello World! I have been seen 1 times. $ curl http://localhost:8000 Hello World! I have been seen 2 times. $ curl http://localhost:8000 Hello World! I have been seen 3 times. ``` 3. Bring the app down: ```console $ docker compose down --volumes Stopping stackdemo_web_1 ... done Stopping stackdemo_redis_1 ... done Removing stackdemo_web_1 ... done Removing stackdemo_redis_1 ... done Removing network stackdemo_default ``` ## Push the generated image to the registry To distribute the web app's image across the swarm, it needs to be pushed to the registry you set up earlier. With Compose, this is very simple: ```console $ docker compose push Pushing web (127.0.0.1:5000/stackdemo:latest)... The push refers to a repository [127.0.0.1:5000/stackdemo] 5b5a49501a76: Pushed be44185ce609: Pushed bd7330a79bcf: Pushed c9fc143a069a: Pushed 011b303988d2: Pushed latest: digest: sha256:a81840ebf5ac24b42c1c676cbda3b2cb144580ee347c07e1bc80e35e5ca76507 size: 1372 ``` The stack is now ready to be deployed. ## Deploy the stack to the swarm 1. Create the stack with `docker stack deploy`: ```console $ docker stack deploy --compose-file docker-compose.yml stackdemo Ignoring unsupported options: build Creating network stackdemo_default Creating service stackdemo_web Creating service stackdemo_redis ``` The last argument is a name for the stack. Each network, volume and service name is prefixed with the stack name. 2. Check that it's running with `docker stack services stackdemo`: ```console $ docker stack services stackdemo ID NAME MODE REPLICAS IMAGE orvjk2263y1p stackdemo_redis replicated 1/1 redis:3.2-alpine@sha256:f1ed3708f538b537eb9c2a7dd50dc90a706f7debd7e1196c9264edeea521a86d s1nf0xy8t1un stackdemo_web replicated 1/1 127.0.0.1:5000/stackdemo@sha256:adb070e0805d04ba2f92c724298370b7a4eb19860222120d43e0f6351ddbc26f ``` Once it's running, you should see `1/1` under `REPLICAS` for both services. This might take some time if you have a multi-node swarm, as images need to be pulled. As before, you can test the app with `curl`: ```console $ curl http://localhost:8000 Hello World! I have been seen 1 times. $ curl http://localhost:8000 Hello World! I have been seen 2 times. $ curl http://localhost:8000 Hello World! I have been seen 3 times. ``` Thanks to Docker's built-in routing mesh, you can access any node in the swarm on port 8000 and get routed to the app: ```console $ curl http://address-of-other-node:8000 Hello World! I have been seen 4 times. ``` 3. Bring the stack down with `docker stack rm`: ```console $ docker stack rm stackdemo Removing service stackdemo_web Removing service stackdemo_redis Removing network stackdemo_default ``` 4. Bring the registry down with `docker service rm`: ```console $ docker service rm registry ``` 5. If you're just testing things out on a local machine and want to bring your Docker Engine out of swarm mode, use `docker swarm leave`: ```console $ docker swarm leave --force Node left the swarm. ```