Docker Swarm

Docker Swarm

1. Set up environment

Update CloudLab Git Repository
  • Create a new branch called docker-swarm from your Docker branch.
  • Update the profile.py in your docker-swarm branch with the content from this profile.py.
Launch CloudLab profile
  • Update your CloudLab profile to see the new branch.
  • Instantiate the experiment.
  • Fill in the parameters as follows:
    • Node type: XenVM or RawPC: XenVM
    • Number of nodes: 2
    • Number of cores in each node: 4
    • MB of RAM in each node: 4096

2. Docker Swarm

SwarmKit
  • Open source tool kit to build multi-node systems
  • Reusable library.
  • Plumbing part of the Docker ecosystem.
  • Adopted into Docker as Docker Swarm
SwarmKit Features
SwarmKit Concepts
  • A cluster will be at least one node.
  • A node can be a manager and a worker.
  • A manager actively takes part in the Raft consensus and keeps the Raft log.
  • You can talk to a manager using the SwarmKit API.
  • One manager is elected as the leader; other manager merely forward requests to it.
  • The workers get their instructions from the managers.
  • Both workers and managers can run containers.
SwarmKit Concepts
  • The managers expose the SwarmKit API.
  • Using the API, you can indicate that you want to run a service.
  • A service is specified by its desired state: which image, how many instances…
  • The leader uses different subsystems to break down services into tasks: orchestrator, scheduler, allocator, dispatcher.
  • A task corresponds to a specific container, assigned to a specific node.
  • Nodes know which tasks should be running, and will start or stop containers accordingly.
Deploying your swarm
  • By default, SwarmKit features are asleep until you active Swarm mode
  • Swarm Mode commands:
    • docker swarm: enable Swarm mode, join Swarm, adjust Swarm’s parameters
    • docker node: view nodes, promote/demote managers, manage nodes
    • docker service: create and manage services.
  • Run the following on head node:


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cd
docker swarm init --advertise-addr eth1:7777 --listen-addr eth1:7777
  • Read the output and use the provided commands on the worker nodes to have these nodes joining the swarm.
  • On the head node, run the following command to view the swarm nodes


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docker node ls

3. Running Applications on Swarm

Local registry
  • Build images for application,
  • Ship these images with a registry,
  • Run services using these images.
    • Why?
    • For docker-compose up, images are built locally for services.
    • For a Swarm, images need to be distributed.
    • The easiest way is to use a Docker registry.
Hands-on: Launching a registry inside Swarm
  • Run the following on the head node


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docker service create --name registry --publish 5000:5000 registry
docker service ps registry
curl 127.0.0.1:5000/v2/_catalog
  • Test your registry
    • This is a demo registry with no security!


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docker pull busybox
docker tag busybox 127.0.0.1:5000/busybox
docker push 127.0.0.1:5000/busybox
curl 127.0.0.1:5000/v2/_catalog
Hands-on: Deploying a service on Swarm
  • Getting the ramcoin app


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git clone https://github.com/CSC468-WCU/ram_coin.git
cd ram_coin
  • Run the following to build and push the images into the local registry


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export REGISTRY=127.0.0.1:5000
export TAG=v0.1
for SERVICE in hasher rng webui worker; do docker build -t $REGISTRY/$SERVICE:$TAG ./$SERVICE; docker push $REGISTRY/$SERVICE:$TAG; done
curl 127.0.0.1:5000/v2/_catalog
  • Launching the overlay network and other services


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docker network create --driver overlay ramcoins
docker service create --network ramcoins --name redis redis
for SERVICE in hasher rng webui worker; do docker service create --network ramcoins --detach=true --name $SERVICE $REGISTRY/$SERVICE:$TAG; done
docker service ls
docker service update webui --publish-add 8000:80
docker service ls
  • Visit the head node at port 8000 to observe the application running.
  • Try scaling up services using: docker service scale SERVICE_NAME=...