Deploy a stack to a swarm
読む時間の目安: 7 分
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.
The docker stack deploy
command supports any Compose file of version “3.0” or
above. If you have an older version, see the upgrade guide.
To run through this tutorial, you need:
-
A Docker Engine running in swarm mode. If you’re not familiar with swarm mode, you might want to read Swarm mode key concepts and How services work.
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
anddocker service
commands must be run from a manager node. -
A current version of Docker Compose.
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 or maintain your own. Here’s how to create a throwaway registry, which you can discard afterward.
-
Start the registry as a service on your swarm:
$ docker service create --name registry --publish published=5000,target=5000 registry:2
-
Check its status with
docker service ls
:$ docker service ls ID NAME REPLICAS IMAGE COMMAND l7791tpuwkco registry 1/1 registry:2@sha256:1152291c7f93a4ea2ddc95e46d142c31e743b6dd70e194af9e6ebe530f782c17
Once it reads
1/1
underREPLICAS
, it’s running. If it reads0/1
, it’s probably still pulling the image. -
Check that it’s working with
curl
:$ 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 guide. It consists of a Python app which maintains a counter in a Redis instance and increments the counter whenever you visit it.
-
Create a directory for the project:
$ mkdir stackdemo $ cd stackdemo
-
Create a file called
app.py
in the project directory and paste this in: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)
-
Create a file called
requirements.txt
and paste these two lines in:flask redis
-
Create a file called
Dockerfile
and paste this in:# syntax=docker/dockerfile:1 FROM python:3.4-alpine ADD . /code WORKDIR /code RUN pip install -r requirements.txt CMD ["python", "app.py"]
-
Create a file called
docker-compose.yml
and paste this in:version: "3.9" 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
-
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.
$ 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
-
Check that the app is running with
docker-compose ps
:$ 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
:$ 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.
-
Bring the app down:
$ 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:
$ 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
-
Create the stack with
docker stack deploy
:$ 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.
-
Check that it’s running with
docker stack services stackdemo
:$ 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
underREPLICAS
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
:$ 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:
$ curl http://address-of-other-node:8000 Hello World! I have been seen 4 times.
-
Bring the stack down with
docker stack rm
:$ docker stack rm stackdemo Removing service stackdemo_web Removing service stackdemo_redis Removing network stackdemo_default
-
Bring the registry down with
docker service rm
:$ docker service rm registry
-
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
:$ docker swarm leave --force Node left the swarm.