AWS EC2 Spot Instance Interrupt Monitor for Graceful Stop

interrupt-monitor.sh

#!/bin/bash

set -o nounset -o pipefail

IMDS_ENDPOINT=${IMDS_ENDPOINT:-"http://169.254.169.254"}
IMDS_VERSION=${IMDS_VERSION:-latest}
MONITOR_INTERVAL=${MONITOR_INTERVAL:-5}

check_dependencies() {
  local dependencies=("jq" "curl")
  local err=false
  for executable in "${dependencies[@]}"; do
    if ! command -v "$executable" > /dev/null; then
      printf "ERROR: Executable '%s' is required, but I could not find it.\n" "$executable" >&2
      err=true
    fi
  done

  if "$err"; then
    printf "Install the missing dependencies and make sure they are available on your PATH.\n" >&2
    printf "I checked using 'command -v EXECUTABLE'.\n" >&2
    exit 1
  fi
}

get_metadata() {
  local path=$1

  local token_ttl=15
  local token
  token=$(curl -sS -X PUT "$IMDS_ENDPOINT/$IMDS_VERSION/api/token" -H "X-aws-ec2-metadata-token-ttl-seconds: $token_ttl")
  curl -sSf -H "X-aws-ec2-metadata-token: $token" "$IMDS_ENDPOINT/$IMDS_VERSION/meta-data/$path" 2> /dev/null
}

should_terminate() {
  local response=$1

  local action
  if action=$(echo "$response" | jq -r ".action") && [ "$action" = "terminate" ]; then
    return 0
  fi

  return 1
}

monitor_interrupt() {
  printf "Monitoring for interruption notice\n"

  local response
  until response=$(get_metadata "spot/instance-action") && should_terminate "$response"; do
    sleep "$MONITOR_INTERVAL"
  done

  printf "Received termination notice!\n"
}

graceful_stop() {
  # =======================================
  # Code to perform graceful stop goes here
  # =======================================
}

check_dependencies
monitor_interrupt
graceful_stop