We are using Cloudflare, which points to an AWS load balancer in front of an EC2 instance. The goal here is to have end-to-end encryption but I am trying to understand which parts of this setup actually require a certificate from a Certificate Authority, and whether or not we can use a complete set of free certificates between Cloudflare and AWS.
Cloudflare - We can use their free Universal SSL certificate to secure the traffic from Cloudflare to the load balancer.
AWS Load Balancer - We can use a free AWS certificate which is attached to the load balancer. This same certificate cannot be installed on the EC2 instance.
EC2 Instance - Can we use a self-signed certificate here, or do we need to continue purchasing certificates from a recognised authority? My understanding here is that, yes, we can just use a self-signed certificate and everything will be secure without raising any warnings about the self-signed nature of the certificate, as long as the load balancer has a valid CA certificate from Amazon or other authority.
Cloudflare is set to Full SSL mode which does not validate the origin certificate and will allow it to be self-signed, but I assume this only applies to the load balancer in our case.
You can use whichever SSL you want on the instance, self signed or from a certificate authority.
By doing this the data will be encrypted in transit between your load balancer and the EC2 instance.
It is only the AWS services that require either an ACM cert or an uploaded cert from a valid certificate authority.
Ensure that your servers are kept private if you're using self signed certificates.