Creating multiple Docker container

Question

I have to create a huge number of Docker container on different hosts (e.g. 50 container each on 3 hosts). These container all have the same image, configuration etc. and only the network address and ID of each container should be different (so basically I want to create a huge virtual container network). Is there a way to achieve this?

I have looked at technologies like Helios and Kubernetes but they seem to only deploy one container on each agent. I thought about just creating a lot of different jobs in Helios and then deploy each one of them to its agent, but that seems a little dirty to me.

Answer 1

For the Docker specific solution, you can use Swarm and Compose.

Create your Docker Swarm cluster of 3 nodes and change your environment to that Swarm. (The below assumes each host is listening on 2375, which is ok for a private network, but you'll want TLS setup and switch over to 2376 for more security.)

cat >cluster.txt <<EOF
node1:2375
node2:2375
node3:2375
EOF
docker run -d -P --restart=always --name swarm-manager \
  -v ./cluster.txt:/cluster.txt \
  swarm manage file:///cluster.txt
export DOCKER_HOST=$(docker port swarm-manager 2375)

Define your service inside of a docker-compose.yml, and then run docker-compose scale my-service=150. If your Swarm is setup with the default spread strategy, it will distribute them across the 3 hosts based on the number of containers running (or stopped) on each.

cat >docker-compose.yml <<EOF
my-app:
  image: my-app
EOF
docker-compose scale my-app=150

Note that the downside of docker-compose over the other tools out there is that it doesn't correct for outages until you rerun it.

Answer 2

This is exactly the type of use case that Kubernetes is well suited for.

You should use a Replica Set. When creating your Replica Set, you specify a template that tells the system how to create each container instance along with a desired number of replicas. It will then create that number of replicas in the available number of nodes in your cluster.

One caveat is that by default, Kubernetes will only allow you to have ~100 pods / node, but you can change this number with a command line flag if you need more.