.. _ray-slurm-deploy:

Deploying on Slurm
==================

Clusters managed by Slurm may require that Ray is initialized as a part of the submitted job. This can be done by using ``srun`` within the submitted script. For example:

.. code-block:: bash

  #!/bin/bash

  #SBATCH --job-name=test
  #SBATCH --cpus-per-task=5
  #SBATCH --mem-per-cpu=1GB
  #SBATCH --nodes=3
  #SBATCH --tasks-per-node 1

  worker_num=2 # Must be one less that the total number of nodes

  # module load Langs/Python/3.6.4 # This will vary depending on your environment
  # source venv/bin/activate

  nodes=$(scontrol show hostnames $SLURM_JOB_NODELIST) # Getting the node names
  nodes_array=( $nodes )

  node1=${nodes_array[0]}

  ip_prefix=$(srun --nodes=1 --ntasks=1 -w $node1 hostname --ip-address) # Making address
  suffix=':6379'
  ip_head=$ip_prefix$suffix
  redis_password=$(uuidgen)

  export ip_head # Exporting for latter access by trainer.py

  srun --nodes=1 --ntasks=1 -w $node1 ray start --block --head --redis-port=6379 --redis-password=$redis_password & # Starting the head
  sleep 5
  # Make sure the head successfully starts before any worker does, otherwise
  # the worker will not be able to connect to redis. In case of longer delay,
  # adjust the sleeptime above to ensure proper order.

  for ((  i=1; i<=$worker_num; i++ ))
  do
    node2=${nodes_array[$i]}
    srun --nodes=1 --ntasks=1 -w $node2 ray start --block --address=$ip_head --redis-password=$redis_password & # Starting the workers
    # Flag --block will keep ray process alive on each compute node.
    sleep 5
  done

  python -u trainer.py $redis_password 15 # Pass the total number of allocated CPUs

.. code-block:: python

  # trainer.py
  from collections import Counter
  import os
  import sys
  import time
  import ray

  redis_password = sys.argv[1]
  num_cpus = int(sys.argv[2])

  ray.init(address=os.environ["ip_head"], redis_password=redis_password)

  print("Nodes in the Ray cluster:")
  print(ray.nodes())

  @ray.remote
  def f():
      time.sleep(1)
      return ray.services.get_node_ip_address()

  # The following takes one second (assuming that ray was able to access all of the allocated nodes).
  for i in range(60):
      start = time.time()
      ip_addresses = ray.get([f.remote() for _ in range(num_cpus)])
      print(Counter(ip_addresses))
      end = time.time()
      print(end - start)