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Add experimental Compose/Swarm/multi-host networking guide
Signed-off-by: Aanand Prasad <aanand.prasad@gmail.com>
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Aanand Prasad
Tibor Vass
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# Experimental: Compose, Swarm and Multi-Host Networking
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The [experimental build of Docker](https://github.com/docker/docker/tree/master/experimental) has an entirely new networking system, which enables secure communication between containers on multiple hosts. In combination with Docker Swarm and Docker Compose, you can now run multi-container apps on multi-host clusters with the same tooling and configuration format you use to develop them locally.
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> Note: This functionality is in the experimental stage, and contains some hacks and workarounds which will be removed as it matures.
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## Prerequisites
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Before you start, you’ll need to install the experimental build of Docker, and the latest versions of Machine and Compose.
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- To install the experimental Docker build on a Linux machine, follow the instructions [here](https://github.com/docker/docker/tree/master/experimental#install-docker-experimental).
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- To install the experimental Docker build on a Mac, run these commands:
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$ curl -L https://experimental.docker.com/builds/Darwin/x86_64/docker-latest > /usr/local/bin/docker
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$ chmod +x /usr/local/bin/docker
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- To install Machine, follow the instructions [here](http://docs.docker.com/machine/).
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- To install Compose, follow the instructions [here](http://docs.docker.com/compose/install/).
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You’ll also need a [Docker Hub](https://hub.docker.com/account/signup/) account and a [Digital Ocean](https://www.digitalocean.com/) account.
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## Set up a swarm with multi-host networking
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Set the `DIGITALOCEAN_ACCESS_TOKEN` environment variable to a valid Digital Ocean API token, which you can generate in the [API panel](https://cloud.digitalocean.com/settings/applications).
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DIGITALOCEAN_ACCESS_TOKEN=abc12345
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Start a consul server:
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docker-machine create -d digitalocean --engine-install-url https://experimental.docker.com consul
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docker $(docker-machine config consul) run -d -p 8500:8500 -h consul progrium/consul -server -bootstrap
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(In a real world setting you’d set up a distributed consul, but that’s beyond the scope of this guide!)
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Create a Swarm token:
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SWARM_TOKEN=$(docker run swarm create)
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Create a Swarm master:
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docker-machine create -d digitalocean --swarm --swarm-master --swarm-discovery=token://$SWARM_TOKEN --engine-install-url="https://experimental.docker.com" --digitalocean-image "ubuntu-14-10-x64" --engine-opt=default-network=overlay:multihost --engine-label=com.docker.network.driver.overlay.bind_interface=eth0 --engine-opt=kv-store=consul:$(docker-machine ip consul):8500 swarm-0
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Create a Swarm node:
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docker-machine create -d digitalocean --swarm --swarm-discovery=token://$SWARM_TOKEN --engine-install-url="https://experimental.docker.com" --digitalocean-image "ubuntu-14-10-x64" --engine-opt=default-network=overlay:multihost --engine-label=com.docker.network.driver.overlay.bind_interface=eth0 --engine-opt=kv-store=consul:$(docker-machine ip consul):8500 --engine-label com.docker.network.driver.overlay.neighbor_ip=$(docker-machine ip swarm-0) swarm-1
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You can create more Swarm nodes if you want - it’s best to give them sensible names (swarm-2, swarm-3, etc).
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Finally, point Docker at your swarm:
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eval "$(docker-machine env --swarm swarm-0)"
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## Run containers and get them communicating
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Now that you’ve got a swarm up and running, you can create containers on it just like a single Docker instance:
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$ docker run busybox echo hello world
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hello world
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If you run `docker ps -a`, you can see what node that container was started on by looking at its name (here it’s swarm-3):
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$ docker ps -a
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CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
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41f59749737b busybox "echo hello world" 15 seconds ago Exited (0) 13 seconds ago swarm-3/trusting_leakey
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As you start more containers, they’ll be placed on different nodes across the cluster, thanks to Swarm’s default “spread” scheduling strategy.
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Every container started on this swarm will use the “overlay:multihost” network by default, meaning they can all intercommunicate. Each container gets an IP address on that network, and an `/etc/hosts` file which will be updated on-the-fly with every other container’s IP address and name. That means that if you have a running container named ‘foo’, other containers can access it at the hostname ‘foo’.
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Let’s verify that multi-host networking is functioning. Start a long-running container:
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$ docker run -d --name long-running busybox top
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<container id>
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If you start a new container and inspect its /etc/hosts file, you’ll see the long-running container in there:
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$ docker run busybox cat /etc/hosts
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...
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172.21.0.6 long-running
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Verify that connectivity works between containers:
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$ docker run busybox ping long-running
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PING long-running (172.21.0.6): 56 data bytes
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64 bytes from 172.21.0.6: seq=0 ttl=64 time=7.975 ms
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64 bytes from 172.21.0.6: seq=1 ttl=64 time=1.378 ms
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64 bytes from 172.21.0.6: seq=2 ttl=64 time=1.348 ms
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^C
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--- long-running ping statistics ---
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3 packets transmitted, 3 packets received, 0% packet loss
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round-trip min/avg/max = 1.140/2.099/7.975 ms
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## Run a Compose application
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Here’s an example of a simple Python + Redis app using multi-host networking on a swarm.
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Create a directory for the app:
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$ mkdir composetest
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$ cd composetest
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Inside this directory, create 2 files.
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First, create `app.py` - a simple web app that uses the Flask framework and increments a value in Redis:
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from flask import Flask
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from redis import Redis
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import os
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app = Flask(__name__)
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redis = Redis(host='composetest_redis_1', port=6379)
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@app.route('/')
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def hello():
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redis.incr('hits')
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return 'Hello World! I have been seen %s times.' % redis.get('hits')
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if __name__ == "__main__":
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app.run(host="0.0.0.0", debug=True)
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Note that we’re connecting to a host called `composetest_redis_1` - this is the name of the Redis container that Compose will start.
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Second, create a Dockerfile for the app container:
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FROM python:2.7
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RUN pip install flask redis
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ADD . /code
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WORKDIR /code
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CMD ["python", "app.py"]
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Build the Docker image and push it to the Hub (you’ll need a Hub account). Replace `<username>` with your Docker Hub username:
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$ docker build -t <username>/counter .
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$ docker push <username>/counter
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Next, create a `docker-compose.yml`, which defines the configuration for the web and redis containers. Once again, replace `<username>` with your Hub username:
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web:
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image: <username>/counter
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ports:
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- "80:5000"
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redis:
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image: redis
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Now start the app:
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$ docker-compose up -d
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Pulling web (username/counter:latest)...
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swarm-0: Pulling username/counter:latest... : downloaded
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swarm-2: Pulling username/counter:latest... : downloaded
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swarm-1: Pulling username/counter:latest... : downloaded
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swarm-3: Pulling username/counter:latest... : downloaded
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swarm-4: Pulling username/counter:latest... : downloaded
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Creating composetest_web_1...
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Pulling redis (redis:latest)...
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swarm-2: Pulling redis:latest... : downloaded
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swarm-1: Pulling redis:latest... : downloaded
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swarm-3: Pulling redis:latest... : downloaded
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swarm-4: Pulling redis:latest... : downloaded
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swarm-0: Pulling redis:latest... : downloaded
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Creating composetest_redis_1...
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Swarm has created containers for both web and redis, and placed them on different nodes, which you can check with `docker ps`:
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$ docker ps
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CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
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92faad2135c9 redis "/entrypoint.sh redi 43 seconds ago Up 42 seconds swarm-2/composetest_redis_1
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adb809e5cdac username/counter "/bin/sh -c 'python 55 seconds ago Up 54 seconds 45.67.8.9:80->5000/tcp swarm-1/composetest_web_1
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You can also see that the web container has exposed port 80 on its swarm node. If you curl that IP, you’ll get a response from the container:
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$ curl http://45.67.8.9
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Hello World! I have been seen 1 times.
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If you hit it repeatedly, the counter will increment, demonstrating that the web and redis container are communicating:
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$ curl http://45.67.8.9
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Hello World! I have been seen 2 times.
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$ curl http://45.67.8.9
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Hello World! I have been seen 3 times.
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$ curl http://45.67.8.9
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Hello World! I have been seen 4 times.
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