AML Compute Instance - Enable Swap Space setup script

enable-swap.sh

#!/bin/bash
# Copyright (c) 2021 Microsoft
# 
# This software is released under the MIT License.
# https://opensource.org/licenses/MIT

# ============================================
# AZURE ML COMPUTE INSTANCE - ENABLE SWAP FILE
# ============================================

# This startup script is intended for Azure ML Compute Instances
# The script will update the /etc/waagent.conf file to include the swap file settings.
# See https://docs.microsoft.com/en-us/troubleshoot/azure/virtual-machines/oom-swap-file-linux-vm
# for more details.

# In choosing the swap size, many different recommendations exist. Since this is intended for
# Azure ML Compute Instance - which is intended for very RAM intensive data manipulation tasks
# we'll use pretty aggressive recommendations - following the "hibernation" guidelines here:
# https://access.redhat.com/documentation/en-us/red_hat_enterprise_linux/7/html/storage_administration_guide/ch-swapspace#tb-recommended-system-swap-space



echo "================="
echo "Create Swap Space"
echo "================="
echo 
RAM_MB=`free -m | awk '/Mem:/ {print $2}'`
SWAP_MB=`free -m | awk '/Swap:/ {print $2}'`

echo "Current:"
echo "    RAM (MB) : " $RAM_MB
echo "    Swap (MB): " $SWAP_MB

echo

# First, determine if the swap space is already set, if it is, then skip
# this step

# NOTE: This logic could be updated to check if the alloted swap size follows the recommended sizing
# But for our purposes, we'll just exit the script if the swap file exists
if [ $SWAP_MB -ne 0 ]; then
  echo "    Swap Already Created - exiting script"
  exit 0
fi


echo "Future:"
# Calculate the future swap size
# Since expr can't multiply float values, we'll
# multiple these by 10, and then divide total by 10 at the end
if [ $RAM_MB -le 2048 ]; then
    # If RAM 2 GB or less, then swap = 3x RAM
    SWAP_RATIO=30
elif [ $RAM_MB -le 8192 ]; then
    # If RAM 2 GB - 8 GB, then swap = 2x RAM
    SWAP_RATIO=20
elif [ $RAM_MB -le 65536 ]; then
    # If RAM 8 GB - 64 GB, then swap = 1.5x RAM
    SWAP_RATIO=15
else
    # Swap == RAM
    SWAP_RATIO=10
fi

SWAP_TIMES_TEN=`expr $RAM_MB \* $SWAP_RATIO`
NEW_SWAP_MB=`expr $SWAP_TIMES_TEN / 10`
echo "    Swap (MB): " $NEW_SWAP_MB

# Set values in waagent.conf
echo
echo "Actions:"
echo "    Creating backup of config file - '/etc/waagent.conf.bak'"
echo "    Updated '/etc/waagent.conf'"

sed -i.bak -e 's/ResourceDisk.Format=.*/ResourceDisk.Format=y/' \
 -e 's/#* *ResourceDisk.EnableSwap=.*/ResourceDisk.EnableSwap=y/' \
 -e "s/#* *ResourceDisk.SwapSizeMB=.*/ResourceDisk.SwapSizeMB=$NEW_SWAP_MB/" /etc/waagent.conf
 
 shutdown -r 1 #reboot in 1 minute

I think there needs to be a form of 'chmod +w /etc/waagent.conf' for this to run without any other intervention. Once I did that manually, it ran great.