Add all instances in an autoscaling group to an equivalently named dns entry.

route53-asg-rrdns.sh

#!/bin/bash
#
# Get all IPs from an autoscale group and update set the local ip as
# equal weight A entries (round robin dns). Takes autoscale group as
# parameter.
#
# Amit Bakshi
# 10/21/2014
#

ZONE_ID=YOURZONEID
DOMAIN=yourdomain.com

[ -n "$1" ] || {
  echo >&2 "Usage: $0 <auto-scaling-group>"
  exit 2
}


asg_ips () {
    local instance_ids="$(aws autoscaling describe-auto-scaling-groups \
                        --auto-scaling-group-names "$1" \
                        --query 'AutoScalingGroups[*].Instances[*].[InstanceId]' --output text)"

    aws ec2 describe-instances --instance-ids $instance_ids \
        --query 'Reservations[*].Instances[*].[PrivateIpAddress]' --output text
}

gen_json () {
    local private_ips=($(asg_ips "$1"))
    cat <<EOF
{
  "Comment": "Modifying autoscale group $1 record for the zone.",
  "Changes": [
    {
    "Action": "UPSERT",
    "ResourceRecordSet": {
        "Name": "$1.${DOMAIN}.",
        "Type": "A",
        "TTL": 300,
        "ResourceRecords": [
EOF

    local -i count=${#private_ips[@]}
    for ((i=0 ; i < $count - 1 ; i ++)); do
    cat <<EOF
            {
                "Value": "${private_ips[$i]}"
            },
EOF
    done
    cat <<EOF
            {
                "Value": "${private_ips[(( $count - 1 ))]}"
            }
EOF
    cat <<EOF
        ]
      }
    }
  ]
}
EOF
}

gen_json "$1" > /tmp/${1}.json
aws route53 change-resource-record-sets --hosted-zone-id $ZONE_ID --change-batch file:///tmp/${1}.json