HTTPS Not Working for Non-WWW Domain on AWS Load Balancer

Hello.

What kind of error occurs when accessing with "https://example.com/"?
If "example.com" is included in the certificate, you should be able to access it normally.
Based on your explanation, it doesn't seem to be a problem, so you might want to try clearing your browser's cache and cookies.

*.example.com and example.com - have the same CNAME, and are added at domain registrar (one CNME record)

Based on the information provided, it appears that the issue is related to the SSL/TLS certificate configuration and DNS settings for your domain. Here are a few potential causes and solutions to consider:

1. Certificate Configuration: Ensure that your SSL/TLS certificate issued by Amazon Certificate Manager (ACM) correctly includes both "example.com" and "www.example.com" as Subject Alternative Names (SANs). The fact that https://www.example.com works but https://example.com doesn't suggests there might be a mismatch in the certificate configuration.

2. DNS Configuration: Double-check your DNS settings at your domain registrar. Make sure that both the root domain (example.com) and the www subdomain (www.example.com) have CNAME records pointing to your load balancer's DNS name. It's possible that the CNAME for the root domain is not correctly set up.

3. Load Balancer Listener: Verify that your load balancer has a listener configured for HTTPS (port 443) that uses the correct SSL/TLS certificate. Ensure that this listener is set up to handle requests for both the www and non-www versions of your domain.

4. Security Groups: Check that the security group associated with your load balancer allows inbound traffic on port 443 (HTTPS) from all sources (0.0.0.0/0).

5. Target Group Configuration: Ensure that your target group is correctly configured to forward traffic to your EC2 instance on the appropriate port (usually 80 for HTTP).

6. EC2 Instance Configuration: Make sure your EC2 instance is properly configured to handle requests coming from the load balancer. This includes having the correct security group rules to allow traffic from the load balancer.

7. Application Configuration: If your application is handling the redirection from HTTP to HTTPS, ensure that it's configured to handle requests for both www and non-www versions of your domain.

To troubleshoot further, you can try accessing https://example.com directly using a tool like curl with the verbose option to see more details about the connection attempt. This might provide additional clues about where the connection is failing.

If all these settings appear correct, you may want to review your load balancer's access logs or your application logs for any error messages that could provide more insight into the issue.

Sources
Troubleshoot a Classic Load Balancer: Client connectivity - Elastic Load Balancing
How to enable HTTPS for domain name (http working) | AWS re:Post
Not able to access my secure site | AWS re:Post
How do I set up SSL to my ec2 instance via a load balancer? | AWS re:Post

Hello, What kind of error occurs when accessing with "https://example.com/"?

"This site can’t be reached The connection was reset. Try: Checking the connection Checking the proxy and the firewall ERR_CONNECTION_RESET"

So pity, it's still the problem, try clearing cash many times.