Benchmarking On-Premise and EC2 Clients Running Against RDS

by Paul Allen

At Cornell, as engineers contemplate moving infrastructure and applications to AWS it is tempting to ask whether they can start just by moving database instances to the AWS Relational Database Service (RDS) and leaving other application components on premise. The reasons behind this probably stem from the fact that the on-premise relational databases represent a very well-defined component with well-defined connectivity to other components. And, tools like the AWS Database Migration Service promise to make the move fairly painless.

So, how feasible is it to leave applications on campus while using an RDS database as a back end? When I queried the Cornell cloud community about this, I got several anecdotal responses that this had been tried, without much success, with web applications.


How to Setup AWS Route53 to Work with Cornell-Managed DNS

by Paul Allen

If you are at Cornell developing and deploying sites or services using AWS, one of the things you’ll usually want to do is ensure that those sites and services can be accessed using a hostname in the domain. Keeping an existing hostname is even more critical if you are moving a service from Cornell infrastructure to AWS infrastructure. This article describes how to use the Cornell DNS system in conjunction with AWS Route53 to deploy services in AWS that respond to host names.


Let’s say we want to deploy a web site running on AWS at URL The Cornell DNS system and Cornell IT policy won’t let you directly reference an AWS IP address in a Cornell DNS “A” record. Further, even if we could do that, we wouldn’t get to take advantage of all the flexibility and features that Route53 offers–for example health checks on backend servers and dynamic failover.

At Cornell, in order to create the hostname, I need to be an administrator of the sub-domain in the Cornell DNS system. I also need privileges to  a public hosted zone in Route53. In this example, I’ll use, a public Route53 hosted zone which I have permissions to administer in AWS.

Here’s the short version of what needs to happen in this scenario:

  1. Setup Route53 to serve content from
  2. Add a CNAME to Cornell DNS so that is an alias for

The rest of this article goes through the specifics of how to accomplish that. This particular example will use:

Step 1 – Get a site running in AWS

This doesn’t necessarily need to be your first step, but the explanation is easier if we start here. In this example I have an EC2 instance running a generic Apache server showing a generic test page. AWS provides very detailed instructions for setting up Apache on an EC2 instance. Right now, you don’t have to worry about any hostnames–the goal is to make sure you have content being delivered from AWS. My example instance is below.

EC2 Instance Configuration

There are many other ways to serve content or applications in AWS, but I’m just picking one of the simplest ways for this article. Other options might include using CloudFront and S3 to serve a static web site or using Elastic Beanstalk to run an application. There are a plethora of other ways to accomplish this as well.

Here are the important things about this instance configuration:

  • It is running in a public subnet with a public IP assigned. In a real situation, we would run the instance on a private subnet. But, this configuration is easier to test as you work through the example.
  • The Security Group (named “dns-example”) attached to the instance allows HTTP (port 80) and SSH (port 22) access from anywhere ( Again, not how we’d setup things in real life, but good enough for now to accomplish our current goals.
  • Apache is installed and running in the instance. You can check that by pointing your browser to the public IP address of your instance as shown below.

Apache is running

Step 2 – Configure an Elastic Load Balancer

Strictly speaking I don’t need an ELB to accomplish my goal, but using an ELB is a best practice and allows us to easily configure Route53 to direct users to our content.

Again, AWS provides step-by-step instructions for creating an ELB and I’ll register the instance I already have running to my new load balancer. Those AWS instructions are great for our situation, except for one thing: the ELB health check configured in the instructions won’t quite work if the only content I’m serving from my instance is that default test page. The reason for that is that the test page returns a HTTP status of code 403 instead of 200.  That 403 code will cause the ELB heath check configured in the instructions to fail and the ELB will take your instance offline. Instead of a having the ELB check whether “http:/” returns a 200 status, we need to loosen that up to a TCP check on port 80 as shown below. The TCP  check just makes sure that something on my instance is accepting connections on port 80. I’ll set the “Healthy threshold” value to 2 so that the ELB will bring my instance back online more quickly–useful for our scenario but maybe not in real life.


Modified ELB Health Check

Besides the health check configuration, the key points of my ELB configuration are highlighted in yellow on the screenshot below:

  • The ELB scheme is “internet-facing”.
  • My EC2 instance is registered with the ELB and it is recognized as healthy (because of the looser health check). I.e., “1 of 1 instances in service”.
  • The ELB is configured to use public subnets in my chosen availability zones.  You’ll have to take my word for it that “subnet-8d95c4fa” and “subnet-8e618aa4” are the public subnets in my VPC.
  • The Source Security Group allows HTTP traffic to the ELB on port 80. In this case I’m using the same security group as I did for my EC2 instance.

ELB Configuration

Note that the ELB “Description” tab also provides you with information about the DNS name for the ELB, highlighted in orange above. You should be able to point your browser to that name and see your test page appear. If not, go back and confirm the key configuration details in your EC2 instance and ELB.

The ELB is serving our test page.

Step 3 – Configure Route53

Now we are ready to get Route53 looped into our configuration.

1. Start by pointing your AWS Console to the Route 53 service.

Route53 in the AWS Console

2. You will need to have privileges over at least one public Route 53 hosted zone. Setting up a public hosted zone is beyond the scope of this article, but contact if you need a hosted zone for your Cornell AWS account but don’t have one. I’ll be using as the hosted zone for this article.

Route 53 Hosted Zone Zone in Route 53

3. In the hosted zone, I’m going to “Create Record Set”.

Route 53 New Record Set

4. In the “Create Record Set” dialog, enter “example” as the name, which will configure the name “”. Ensure that the record type is “A – IPv4 address”. Select “Yes” for “Alias.” and then choose your ELB from the dropdown menu. Leave the remaining items with their default values, and select the “Create” button.

Route 53 Alias Record

This should have created a new name in your hosted zone. That’s great, but you might find yourself asking what the heck is an “Alias” record? AWS calls the Route53 Alias functionality an “extension” to the standard DNS system as we know it. Alias records in Route 53 will automatically track changes in certain AWS resources and always ensure that a Route 53 name points to the right IP address. For example, if the IP address of our ELB ever changes, the Alias functionality will automatically track that change and keep our name working. AWS documentation contains more about deciding between alias and non-alias records. If you go back and look at the fine print on the ELB “Description” tab you will see a warning there about avoiding using the IP address of an ELB in DNS records because, over time, the IP address of the ELB may change through no fault of your own.

Route 53 Name

5. Now you should be able to point your browser at the new Route 53 name and see your test page being delivered from your EC2 instance via the ELB.

Test Route 53 Name

You are now done with the AWS side of things. Time to move on to Cornell DNS.

Step 4 – Configure Cornell DNS

The goal in this step is to setup a new CNAME in the Cornell DNS system pointing to the new Route 53 name we just created. You will need admin privileges to the Cornell sub-domain in which you want to create the name. Here, I have privileges to the sub-domain.

1. Navigate to the Cornell DNS batch processing interface. You will need to authenticate with your Cornell netID to access the batch interface.

2. Enter “addcname [your-host-and-subdomain] [your-route-53-name]” into the batch processor. The batch command for this example is “addcname”. Also be sure to check the box that says “Allow cnames and mx records to point to targets outside your subnets and domains”.

Cornell Batch Processor Input

This should result in output confirming that the CNAME was created.

Cornell Batch Processor Output

3. Now wait. The Cornell DNS changes may not take effect immediately. In the worst case, they are pushed out about 5-10 minutes after the top of each hour. You can use ping to test whether the Cornell name has been published. E.g., “ping”. As soon as ping stops reporting that it cannot resolve the name, you are in business.

4. Point your browser to your new Cornell DNS name. If you see your your AWS Apache test page, you have achieved your goal. If not go back and troubleshoot, examining the key configuration items pointed out earlier in this article.

Final Result


Now that you know how to configure an AWS service to respond to Cornell DNS names, there are several things you might want to do to transform this example into something nearing a production configuration.

  • To achieve better fault tolerance, add more EC2 instances serving your content/service. You might even want to setup an AWS autoscaling group. If you manually add instances, be sure not to forget to register them with your ELB.
  • Instead of running EC2 instances on public subnets, move them to your private subnets to better protect them from the bad guys.
  • Review the Security Groups you used for the ELB and your EC2 instance(s). Improve them by reducing access to the minimum needed for your service. That might mean allowing only HTTP/HTTPS traffic on ports 80 and 443 to your ELB. For the EC2 instance(s), you could reduce the scope of traffic on ports 22, 80, 443 to just the IP range in your VPC subnets. Be sure that the ELB sitting on your public subnet(s) can still access the appropriate ports (e.g., 80, 443) on your EC2 instances. Also be sure not to block yourself from getting to port 22 if you need to admin your EC2 instance(s).
  • Once you begin serving real content on your backend server (i.e., not the default test page), change the ELB health check to use an HTTP or HTTPS check.
  • Consider adding health checks and failover to your Route 53 configuration.
  • Setup the ELB to serve HTTPS traffic by uploading a server certificate into AWS Identity and Access Management Service and configuring your ELB to use it.
  • Turn on access logging for the ELB.