Distributed Training with RayCluster

In this guide, we will walk through the process of setting up a Ray cluster on MicroK8s with multiple nodes and launching a Schola training script on it. We will cover the necessary installations and configurations for MicroK8s, Docker, and Ray. It is important to note that this is not the only way to set up a Ray cluster or launch training scripts, and the configurations can be customized based on your specific requirements. However, this guide provides a starting point for distributed training using Ray on a local Kubernetes cluster.

Install Prerequisites

Before we begin, ensure that you have the following prerequisites installed on your system:

Ubuntu 22.04 (22.04.4 Desktop x86 64-bit is recommended for reproducibility)
Docker (Ensure Docker is installed and running)
MicroK8s (A lightweight Kubernetes distribution)
Ray (A framework for building and running distributed applications)

Note

Ensure that you have sudo privileges to install and configure the above tools.

Setting Up Docker

Uninstall Conflicting Docker Packages if Necessary:

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sudo apt-get purge docker-ce docker-ce-cli containerd.io docker-buildx-plugin docker-compose-plugin docker-ce-rootless-extras
sudo rm -rf /var/lib/docker
sudo rm -rf /var/lib/containerd
for pkg in docker.io docker-doc docker-compose docker-compose-v2 podman-docker containerd runc; do sudo apt-get remove $pkg; done

Install Docker:

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sudo apt-get update
sudo apt-get install ca-certificates curl
sudo install -m 0755 -d /etc/apt/keyrings
sudo curl -fsSL https://download.docker.com/linux/ubuntu/gpg -o /etc/apt/keyrings/docker.asc
sudo chmod a+r /etc/apt/keyrings/docker.asc
echo "deb [arch=$(dpkg --print-architecture) signed-by=/etc/apt/keyrings/docker.asc] https://download.docker.com/linux/ubuntu $(. /etc/os-release && echo "$VERSION_CODENAME") stable" | sudo tee /etc/apt/sources.list.d/docker.list > /dev/null
sudo apt-get update
sudo apt-get install docker-ce docker-ce-cli containerd.io docker-buildx-plugin docker-compose-plugin

Post Docker Installation:

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sudo groupadd docker
sudo usermod -aG docker $USER
newgrp docker
docker run hello-world
sudo systemctl enable docker.service
sudo systemctl enable containerd.service

Configure Docker Registry:

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docker run -d -p <your_registry_ip>:32000:5000 --name registry registry:2
cat <<EOF | sudo tee /etc/docker/daemon.json
{
  "insecure-registries": ["<your_registry_ip>:32000"]
}
EOF
sudo systemctl restart docker
docker start registry

Setting Up MicroK8s

Uninstall Existing MicroK8s if Necessary:

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if command -v microk8s &> /dev/null; then
  sudo microk8s reset
  sudo snap remove microk8s
fi
sudo rm -rf /var/snap/microk8s/current

Install MicroK8s:

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sudo snap install microk8s --classic
microk8s status --wait-ready

Add Your User to the MicroK8s Group:
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```
sudo usermod -a -G microk8s $USER
sudo chown -f -R $USER ~/.kube
```
Note

Log out and back in to apply the group changes.
Enable Necessary MicroK8s Services:
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```
microk8s enable dns storage registry
```

Configure MicroK8s to Use Local Docker Registry:

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sudo mkdir -p /var/snap/microk8s/current/args/certs.d/<your_registry_ip>:32000
cat <<EOF | sudo tee /var/snap/microk8s/current/args/certs.d/<your_registry_ip>:32000/hosts.toml
server = "http://<your_registry_ip>:32000"
[host."http://<your_registry_ip>:32000"]
capabilities = ["pull", "resolve"]
EOF
sudo systemctl restart docker
sudo snap stop microk8s
sudo snap start microk8s
microk8s status --wait-ready

Test MicroK8s Setup:

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docker start registry
docker pull hello-world
docker tag hello-world <your_registry_ip>:32000/hello-world
docker push <your_registry_ip>:32000/hello-world
microk8s kubectl create deployment hello-world --image=<your_registry_ip>:32000/hello-world
sleep 2
microk8s kubectl get deployments

Add Nodes to MicroK8s Cluster:

To add a new node, first install MicroK8s on the new machine:
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```
sudo snap install microk8s
```
Then, on the main node, generate the join command:
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```
join_command=$(microk8s add-node | grep 'microk8s join' | grep 'worker')
```
Run the join command on the new node:
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```
microk8s join <main_node_ip>:25000/<token>
```
Update configuration files on the new node to pull images from the local registry (Follow steps 5 in this section and 4 from Docker setup):
- Update /var/snap/microk8s/current/args/certs.d/<your_registry_ip>:32000/hosts.toml
- Update /etc/docker/daemon.json
- Restart the container runtime:
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```
sudo systemctl restart docker
sudo snap stop microk8s
sudo snap start microk8s
```

Building and Deploying the Docker Image

Create a Dockerfile:

Use the following Dockerfile as a reference to build your Docker image:

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FROM rayproject/ray:latest-py39
COPY . ./python
RUN sudo apt-get update && cd python && python -m pip install --upgrade pip && \\
    pip install .[all] && pip install --upgrade numpy==1.26 && \\
    pip install --upgrade ray==2.36 && pip install tensorboard
WORKDIR ./python

Build the Docker Image:

Navigate to the directory containing your Dockerfile and run:
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```
docker build --no-cache -t <image_name>:<tag> .
```

Push the Docker Image to the MicroK8s Registry:

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docker tag <image_name>:<tag> localhost:32000/<image_name>:<tag>
docker push localhost:32000/<image_name>:<tag>

Configuring the Ray Cluster

Install KubeRay Operator:

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microk8s helm repo add kuberay https://ray-project.github.io/kuberay-helm/
microk8s helm repo update
microk8s helm install kuberay-operator kuberay/kuberay-operator --version 1.1.1
sleep 2
microk8s kubectl get pods -o wide

Create a RayCluster Config File:

You may use the following YAML configuration as reference when defining your Ray cluster:

raycluster.yaml

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apiVersion: ray.io/v1
kind: RayCluster
metadata:
  annotations:
    meta.helm.sh/release-name: raycluster
    meta.helm.sh/release-namespace: default
  labels:
    app.kubernetes.io/instance: raycluster
    app.kubernetes.io/managed-by: Helm
    helm.sh/chart: ray-cluster-1.1.1
  name: raycluster-kuberay
  namespace: default
spec:
  headGroupSpec:
    rayStartParams:
      dashboard-host: 0.0.0.0
    serviceType: ClusterIP
    template:
      spec:
        containers:
        - image: <cluster IP>:32000/ScholaExamples:registry
          imagePullPolicy: Always
          name: ray-head
          resources:
            limits:
              cpu: "8"
              memory: 48Gi
            requests:
              cpu: "2"
              memory: 16Gi
        volumes:
        - emptyDir: {}
          name: log-volume
  workerGroupSpecs:
  - groupName: workergroup
    maxReplicas: 5
    minReplicas: 3
    replicas: 3
    template:
      metadata:
        labels:
          app: worker-pod
      spec:
        containers:
        - image: <cluster IP>:32000/ScholaExamples:registry
          imagePullPolicy: Always
          name: ray-worker
          resources:
            limits:
              cpu: "8"
              memory: 32Gi
            requests:
              cpu: "3"
              memory: 6Gi
        volumes:
        - emptyDir: {}
          name: log-volume
      imagePullSecrets: []
      nodeSelector: {}
      tolerations: []
      volumes:
      - emptyDir: {}
         name: log-volume
workerGroupSpecs:
- groupName: workergroup
   maxReplicas: <max number of worker pods>
   minReplicas: <min number of worker pods>
   numOfHosts: 1
   rayStartParams: {}
   replicas: 3
   template:
      metadata:
      labels:
         app: worker-pod
      spec:
      affinity:
         podAntiAffinity:
            preferredDuringSchedulingIgnoredDuringExecution:
            - weight: 100
            podAffinityTerm:
               labelSelector:
                  matchExpressions:
                  - key: app
                     operator: In
                     values:
                        - worker-pod
               topologyKey: "kubernetes.io/hostname"
      containers:
      - image: <cluster IP>:32000/ScholaExamples:registry
         imagePullPolicy: Always
         name: ray-worker
         resources:
            limits:
               cpu: "<num cores>"
               memory: <memory to use>Gi
            requests:
               cpu: "<num cores per worker>"
               memory: <memory per worker>Gi
         securityContext: {}
      imagePullSecrets: []
      nodeSelector: {}
      tolerations: []
      volumes:
      - emptyDir: {}
         name: log-volume

Deploy RayCluster:

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microk8s helm install raycluster kuberay/ray-cluster --version 1.1.1
sleep 2
microk8s kubectl get rayclusters
sleep 2
microk8s kubectl get pods --selector=ray.io/cluster=raycluster-kuberay
sleep 2
echo "Ray Cluster Pods:"
microk8s kubectl get pods -o wide

Verify Ray Cluster Setup:

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export HEAD_POD=$(kubectl get pods --selector=ray.io/node-type=head -o custom-columns=POD:metadata.name --no-headers)
echo $HEAD_POD

get_head_pod_status() {
    HEAD_POD=$(microk8s kubectl get pods --selector=ray.io/node-type=head -o custom-columns=POD:metadata.name --no-headers)
    microk8s kubectl get pods | grep $HEAD_POD | awk '{print $3}'
}

head_pod_status=$(get_head_pod_status)
while [ "$head_pod_status" != "Running" ]; do
    echo "Current head pod ($HEAD_POD) status: $head_pod_status. Waiting for 'Running'..."
    sleep 2
    head_pod_status=$(get_head_pod_status)
done

kubectl exec -it $HEAD_POD -- python -c "import ray; ray.init(); print(ray.cluster_resources())"

Deploying the Ray cluster

Apply the configuration to your MicroK8s cluster:

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microk8s kubectl apply -f raycluster.yaml

Launching the Training Script

Execute the Training Script on the Ray Cluster:

The following command is used to launch the training script on the Ray cluster:
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```
microk8s kubectl exec -it $HEAD_POD -- python Schola/Resources/python/schola/scripts/ray/launch.py \\
--num-learners <num_learners> --num-cpus-per-learner <num_cpus_per_learner> \\
--activation <activation_function> --launch-unreal \\
--unreal-path "<path_to_unreal_executable>" -t <training_iterations> \\
--save-final-policy -p <port> --headless <APPO/IMPALA>
```
Key Components of the Command:
- --unreal-path "<path_to_unreal_executable>": This parameter specifies the path to a fully built Unreal Engine executable. It is crucial that this executable is included in the Docker image and accessible at runtime. The Unreal Engine instance is launched as part of the training process, enabling simulations or environments required for training.
- --num-learners <num_learners>: Specifies the number of environment learners to use during training. This can be adjusted based on the available resources and the complexity of the task.
- --num-cpus-per-learner <num_cpus_per_learner>: Defines the number of CPU cores allocated per learner. Adjust this parameter to optimize resource usage and performance.
- --activation <activation_function>: Sets the activation function used in the neural network model. This can be modified to experiment with different activation functions.
- Additional parameters such as -t <training_iterations> (training iterations), --save-final-policy, and -p <port> (port) can be customized to suit specific training requirements.
Note

The options provided in this example are specific to a particular use case. There are many other options available to control the training process, and you should choose the ones that best fit your needs. Refer to the documentation of your training script for a comprehensive list of configurable parameters.

Monitor the Training Process:

Optionally, start a TensorBoard instance to track the training:

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#!/bin/bash

HEAD_POD=$(microk8s kubectl get pods --selector=ray.io/node-type=head -o custom-columns=POD:metadata.name --no-headers)
microk8s kubectl exec -it $HEAD_POD -- tensorboard --logdir /path/to/logs --host 0.0.0.0