Automatic Route53 DNS Entries using Shell Script

Alright ! How to deal with tons of Route53 entries to be created in AWS ?

Two Ways:

  1. Using AWS Console, i.e., manually one by one
  2. Using automation, i.e., using shell scripts or other automation tool (terraform/ansible/blah/blah).

For this, I am using shell scripting to only add new entries to Route53. I’ll explain the code in sections below.

Basic stuff

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#!/bin/bash

export PATH=/usr/local/bin:/usr/bin:/bin:/usr/sbin:/sbin
alias aws=''"$(which aws)"' --profile <PROFILE_NAME> --output text'
shopt -s expand_aliases

The above code will make use of proper PATHs and will not break any commands in the script (read command not found).

Main Logic

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DNSFILE="$2"
DOMAINNAME="$1"
TIMESTAMP=$(date +%s)
export MXCOUNT=$(cut -d, -f2 "$DNSFILE" | grep -i -c MX)

# Create Hosted Zone
HOSTEDZONE_ID="$(aws route53 create-hosted-zone --name "$DOMAINNAME" --caller-reference "$TIMESTAMP" --query 'HostedZone.Id' | cut -d\/ -f3)"
sleep 5
IFS=','
while read DNSNAME DNSTYPE DNSVALUE
do
	case "$DNSTYPE" in
		a|A)  		  		addArecord "$DNSNAME" "$DNSVALUE"		; sleep 5   ;;
		cname|CNAME)  		addCNAMErecord "$DNSNAME" "$DNSVALUE"	; sleep 5 ;;
		mx|MX)  		  	mxrecfunc ;;
		*)	echo "Work in progress; Do manually";;
	esac
done < "$DNSFILE"

The script takes 2 arguments as input to the script.

  • DNSFILE: CSV file containing the DNS records in csv format. More details on this later
  • DOMAINNAME: Domain name for which Hosted zone and DNS records are to be created.

Other variables:

  • TIMESTAMP: Unique timestamp to create a hosted zone. The one I have used is in epoch format.
  • MXCOUNT: To calculate the number of MX records present in CSV file. Used in functions later.

The above code will do the following in series of steps:

  1. Create Hosted Zone and store the ID in HOSTEDZONE_ID variable.
  2. For each line in the DNSFILE file, call the corresponding function to create the record. Currently, only A, CNAME and MX records can be updated by the script. For other’s it will be updated later on Github itself.

A Record function

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addArecord () {
# Add A records
ARECJSON="$(echo '{
	"Comment": "A Record for '"$1"'",
	"Changes": [
	{
		"Action": "CREATE",
		"ResourceRecordSet": {
			"Name": "'"$1"'",
			"Type": "A",
			"TTL": 300,
			"ResourceRecords": [
			{
				"Value": "'"$2"'"
			}
			]
		}
	}
	]
}')"

aws route53 change-resource-record-sets --hosted-zone-id "$HOSTEDZONE_ID" --change-batch "$ARECJSON"
}

Usage

addArecord $DNSNAME $DNSVALUE

Since AWS change-resource-record-sets command accepts JSON, so I had to create a JSON in a variable to use it. The function takes 2 arguments as input.

Example:

addArecord testexample.com 1.2.3.4

CNAME Record

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addCNAMErecord () {
# Add CNAME records
CNAMERECJSON="$(echo '{
  "Comment": "CNAME Record for '"$2"'",
  "Changes": [
    {
      "Action": "CREATE",
      "ResourceRecordSet": {
        "Name": "'"$1"'",
        "Type": "CNAME",
        "TTL": 300,
        "ResourceRecords": [
          {
            "Value": "'"$2"'"
          }
        ]
      }
    }
  ]
}')"
aws route53 change-resource-record-sets --hosted-zone-id "$HOSTEDZONE_ID" --change-batch "$CNAMERECJSON"
}

Similar is the case of CNAME record. Only thing to take care of is this:

addCNAMErecord www.testexample.com test example.com (CORRECT)

and not

addCNAMErecord testexample.com www.testexample.com (WRONG)

MX Records

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addMXrecord () {

# Add MX records
MXRECJSON="$(echo -e '{
  "Comment": "MX Record for '"$DOMAINNAME"'",
  "Changes": [
    {
      "Action": "CREATE",
      "ResourceRecordSet": {
        "Name": "'"$DOMAINNAME"'",
        "Type": "MX",
        "TTL": 300,
        "ResourceRecords": [
          {
            "Value": "'"$2"'"
          }
        ]
      }
    }
  ]
}')"
aws route53 change-resource-record-sets --hosted-zone-id "$HOSTEDZONE_ID" --change-batch "$MXRECJSON"
}

addMultipleMXrecord () {
unset MX_RECORDS
while read -r line; do 
  MX_RECORDS+=( ""$(python -c 'import json, sys; print(json.dumps([{"Value": v} for v in sys.argv[1:]]))' "$line")"" )
done < <(grep -i MX "$DNSFILE" | cut -d, -f3)

DNSVALUES="$(echo "${MX_RECORDS[@]}" | jq -c -s add)"

# Add MX records
MXRECJSON="$(echo -e '{
  "Comment": "MX Record for '"$DOMAINNAME"'",
  "Changes": [
    {
      "Action": "CREATE",
      "ResourceRecordSet": {
        "Name": "'"$DOMAINNAME"'",
        "Type": "MX",
        "TTL": 300,
        "ResourceRecords": '"$DNSVALUES"'
      }
    }
  ]
}')"
aws route53 change-resource-record-sets --hosted-zone-id "$HOSTEDZONE_ID" --change-batch "$MXRECJSON"
}

mxrecfunc() {
  if [[ "$MXCOUNT" == 1 ]]; then
    addMXrecord "$DNSNAME" "$DNSVALUE"
    sleep 5
  else
    addMultipleMXrecord
    sleep 5
  fi
}

Updating MX records is tricky. The values can be 1 or more than 1. For DNS with single MX record is easy. However, updating with 2 MX records cause replacing of 1st MX with the 2nd one.

Here, we are using 3 functions addMXrecord, addMultipleMXrecord and mxrecfunc.

addMXrecord

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addMXrecord () {

# Add MX records
MXRECJSON="$(echo -e '{
  "Comment": "MX Record for '"$DOMAINNAME"'",
  "Changes": [
    {
      "Action": "CREATE",
      "ResourceRecordSet": {
        "Name": "'"$DOMAINNAME"'",
        "Type": "MX",
        "TTL": 300,
        "ResourceRecords": [
          {
            "Value": "'"$2"'"
          }
        ]
      }
    }
  ]
}')"
aws route53 change-resource-record-sets --hosted-zone-id "$HOSTEDZONE_ID" --change-batch "$MXRECJSON"
}

The above code is similar to A records and CNAME records, and is applicable for 1 MX record only.

addMultipleMXrecord

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addMultipleMXrecord () {
unset MX_RECORDS
while read -r line; do 
  MX_RECORDS+=( ""$(python -c 'import json, sys; print(json.dumps([{"Value": v} for v in sys.argv[1:]]))' "$line")"" )
done < <(grep -i MX "$DNSFILE" | cut -d, -f3)
DNSVALUES="$(echo "${MX_RECORDS[@]}" | jq -c -s add)"

# Add MX records
MXRECJSON="$(echo -e '{
  "Comment": "MX Record for '"$DOMAINNAME"'",
  "Changes": [
    {
      "Action": "CREATE",
      "ResourceRecordSet": {
        "Name": "'"$DOMAINNAME"'",
        "Type": "MX",
        "TTL": 300,
        "ResourceRecords": '"$DNSVALUES"'
      }
    }
  ]
}')"
aws route53 change-resource-record-sets --hosted-zone-id "$HOSTEDZONE_ID" --change-batch "$MXRECJSON"
}

Here, the code gets a little nasty. For multiple MX values, ResourceRecords require Key Value in JSON format. So to get the code in JSON, I had to use a small python snippet to get values in array.

End result:

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[
  {
    "Value": "1 A"
  },
  {
    "Value": "2 B"
  }
]

or 

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[{"Value":"1 A"},{"Value":"2 B"}]

Since the above have 2 values, it can be used to update MX records easily.

mxrecfunc

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mxrecfunc() {
  if [[ "$MXCOUNT" == 1 ]]; then
    addMXrecord "$DNSNAME" "$DNSVALUE"
    sleep 5
  else
    addMultipleMXrecord
    sleep 5
  fi
}

The above function simply checks for the count of MX records in DNS file. If the count is 1, then addMXrecord is called, else addMultipleMXrecord.

DNS File Contents/Format

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testexample.com,A,1.2.3.4
qa.testexample.com,A,4.3.2.1
ftp.testexample.com,CNAME,testexample.com
www.testexample.com,CNAME,testexample.com
testexample.com,MX,5 testexample1.com
testexample.com,MX,10 testexample2.com

Screenshots

Terminal Output

AWS Console Output

Code is available on Github

NOTES:

  1. I am not responsible for any command not working, it’s working for me as intended.
  2. Suggestions/Edits are welcome.
  3. Use of Python and jq are incorporated, make sure they are installed and configured properly.
amazon web services aws route53 json dns aws cli
  1. Basic stuff
  2. Main Logic
    1. Other variables:
  3. A Record function
    1. Usage
  4. CNAME Record
  5. MX Records
    1. addMXrecord
    2. addMultipleMXrecord
    3. mxrecfunc
  6. DNS File Contents/Format
  7. Screenshots
    1. Terminal Output
    2. AWS Console Output
  • NOTES:
    • © 2024 Varun Chandak, Powered by Aloha and Hexo.