Updating Route53 DNS Records – Customizing AWS Elastic Beanstalk

In this post let us see how to add or change DNS records using Amazon Route53 and the script we use for that is route53-update-dns.sh. At hudku.com we are using Route53. If you are not using Route53 then this script would fail, but should be harmless and should not affect the deployment of your application using AWS Elastic Beanstalk.Let us have our directory structure. With this post we would be covering the scripts in the “setup” directory completely.

What we are trying to achieve in this script is whenever we deploy a new version of our application onto a staging or development environment, the new application should become available at myAppName-staging.myDomainName.com and the EC2 instance which is the leader of the auto scaling group should become available at ec2.myAppName-staging.myDomainName.com. If it is development environment then the URL should be according to the settings of the development environment.

The URL values for staging and development are obtained from the environment variables ROUTE53_RR_STAGING_NAME and ROUTE53_RR_DEVELOPMENT_NAME which are present in the file “.elastic-beanstalk-app“.

The convenience we get is that we could easily start testing the newly deployed application. Using the EC2 URL we could ssh into the instance without changing the URL in the Putty or other similar tool. Whenever a new Beanstalk environment is created, we do not have to go to the EC2 console to obtain the new Endpoint URL of the instance.

The script first checks whether the deployment is happening on the production environment. If so the DNS records of the production should already have correct settings and hence the script exits. Next the Beanstalk environment name is checked to be in a particular format we use while creating the environment. If the format is unknown then we do not do anything.

In the last section of the script the two DNS records are setup, one for the application and the other for accessing the EC2 instance. If the records do not exist then they are newly created, otherwise the existing records are modified. For the application URL it is an AliasTarget record and for EC2 it is a CNAME record. We make use of route53 command line utility to work with Route53 DNS records.

In case of a development environment, if the environment is created newly and if a previous development environment exists, we try to swap the CNAME of the environments. The idea is to discard the newly generated random CNAME by Beanstalk and instead inherit the CNAME used by the previous development environment.

That’s all about updating the Route53 DNS records after deploying an application in the AWS Elastic Beanstalk environment. We now have completed all the scripts we need. In the next post we shall discuss the main setup script which puts all these pieces together. Please do not miss it.

Here is the source code of route53-update-dns.sh.

#!/bin/bash
 
 
# Execute "export DEBUG=1" to debug this script.
# Set value to 2 to debug this script and the scripts called within this script.
# Set value to 3,4,5 and so on to increase the nesting level of the scripts to be debugged.
[[ $DEBUG -gt 0 ]] && set -x; export DEBUG=$(($DEBUG - 1))
 
 
#
# Update Route53 DNS records for current EC2 instance
#
 
 
# include all the utility scripts
source $ELASTICBEANSTALK_APP_SCRIPT_DIR/include/include.sh
 
 
 
# If we are a production machine then do nothing as DNS records should already be in place
ipProduction=$(getIPOfURL "$ROUTE53_RR_PRODUCTION_NAME")
ipCurELB=$(getIPOfURL "$ELB_URL")
if [ ! -z "$ipProduction" ] && [ ! -z "$ipCurELB" ]; then
    if [ "$ipProduction" == "$ipCurELB" ]; then
        exit 0
    fi
fi 
 
 
envName=$ELASTICBEANSTALK_ENV_NAME
 
# Check envName format
testEnvName=$(echo $envName | grep "^env-[0-9]\{8\}-[0-9]\{4\}$")
if [ -z "$testEnvName" ]; then
    echo "Error: Environment Name is '$envName' whose format is unknown. DNS records are not updated."
    exit 1
fi
 
 
route53RRName=$ROUTE53_RR_STAGING_NAME
if [ "$EC2_INSTANCE_TYPE" == "t1.micro" ]; then
    route53RRName=$ROUTE53_RR_DEVELOPMENT_NAME
fi
 
if [ -z "$route53RRName" ]; then
    echo "Error: Route53 Resource Record Name is not provided. DNS records are not updated."
    exit 1
fi
 
route53HostedZoneID=$ROUTE53_ZONE_ID
 
elbURL=$ELB_URL
elbHostedZoneId=$ELB_HOSTEDZONE_ID
 
 
# If development environment swap the elasticbeanstalk URLs if necessary
if [ "$route53RRName" == "$ROUTE53_RR_DEVELOPMENT_NAME" ]; then
     
    ipPrevDevelopment=$(getIPOfURL "$route53RRName")
    if [ ! -z "$ipPrevDevelopment" ] && [ ! -z "$ipCurELB" ]; then
        if [ "$ipPrevDevelopment" != "$ipCurELB" ]; then
             
            elbURLPrevDevelopment=$($ELASTICBEANSTALK_APP_SCRIPT_DIR/util/elb-get-url-from-ip.sh $ipPrevDevelopment) 
            envNamePrevDevelopment=$($ELASTICBEANSTALK_APP_SCRIPT_DIR/util/elastic-beanstalk-get-env-name-from-elb-url.sh $elbURLPrevDevelopment)
             
            # Swap Elastic Beanstalk CNAME records after some minutes by which time environment creation would have been completed
            echo "Swapping Elastic Beanstalk development environment URLs $envName and $envNamePrevDevelopment"
            elastic-beanstalk-swap-environment-cnames -s $envNamePrevDevelopment -d $envName | at now + 32 minutes
              
        fi
    fi 
fi
 
 
 
ipCur=$(getIPOfURL "$route53RRName")
 
# Update DNS records only if necessary
if [ -z "$ipCur" ] || [ -z "$ipCurELB" ] || [ "$ipCur" != "$ipCurELB" ]; then
     
    # Update AliasTarget record to point to the Load Balancer
    aliasTargetRecord=$(route53 get $route53HostedZoneID | grep -i "^$route53RRName")
    if [ -z "$aliasTargetRecord" ]; then
        # Add the new ALIAS record
        route53 add_alias $route53HostedZoneID $route53RRName A $elbHostedZoneId $elbURL
    else
        # Change existing ALIAS record
        route53 change_alias $route53HostedZoneID $route53RRName A $elbHostedZoneId $elbURL
    fi
  
    # Update EC2 CNAME record
    cnameRecord=$(route53 get $route53HostedZoneID | grep -i "^ec2.$route53RRName")
    if [ -z "$cnameRecord" ]; then
        # Add the new CNAME record
        route53 add_record $route53HostedZoneID ec2.$route53RRName CNAME "$EC2_INSTANCE_URL" 300
    else
        # Change existing CNAME record
        route53 change_record $route53HostedZoneID ec2.$route53RRName CNAME "$EC2_INSTANCE_URL" 300
    fi
         
fi