There are AWS questions that I don’t know the answer to – and sometimes these questions need answers. In a case about a week ago, the following question was posed:
How does an Amazon Web Services ELB function when the backend instances utilize a self-signed certificate?
I was lucky enough to have the time to investigate. If you are just looking for the answer, see “short answer” below. For instructions (and a CloudFormation file) to allow you to duplicate my work, see”long answer” further below.
Yes. The AWS ELB will work with backend instances that utilize a self-signed certificate.
if you’d like to duplicate the test I utilized a CloudFormation file that builds this very infrastructure (an ELB, an Auto Scaling Group and Ubuntu instances running Apache accepting HTTPS connections on port 443) you can get this file from my “Snippets” repository at https://github.com/colinbjohnson/snippets/tree/master/aws/elb/elb_backend_selfsigned_cert A diagram describing the configuration is below:
After performing tests to ensure that the backend instances where healthy and serving requests I wanted to dig a bit deeper to confirm that the data was, in fact, encrypted. I went ahead and ran some requests against the backend web servers and utilized tcpdump on a backend instance, capturing data on port 443. Please note that the Security Group utilized in testing only allows port 443 inbound, so I could have run this test without filtering on “port”. A screen capture of the data captured by tcpdump is shown below:
I ran another tcpdump capture and loaded the data into Wireshark for visualization – the result is show below:
Notice that the capture has no filters applied – and specifically – that payload is shown as “Encrypted Application Data.” If this were an HTTP connection I would be able to view the data that was being sent. After the packet capture my curiosity was satisfied – the body of HTTP requests was being encrypted in transit.
If you require “end to end” encryption of data in transit you can utilize backend instances with self-signed certificates.