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I have used HTTPS for AWS Application Load Balancer listener by using ACM certificate.

I requested the public certificate for a subdomain from ACM: test.example.com and create a CNAME in route 53 for it:

Name: _xxxxxxxxxxx.test.example.com

Type: CNAME

Value: xxxxxx.xxx.acm-validations.aws.

I can use the DNS of ALB (xxxx.us-east-1.elb.amazonaws.com) to call the API successfully in POSTMAN, however, when I use python requests or cURL to call the same API, it will always tell me there is some issue with the SSL.

cURL:

Code:

curl -X POST 
 https://xxxxx.us-east-1.elb.amazonaws.com/prod/testapi 
 -H 'Content-Type: application/json' 
 -H 'cache-control: no-cache' 
 -d '
 "paras1": "xxxxx"
'

Error:

* SSL connection using TLSv1.2 / ECDHE-RSA-AES128-GCM-SHA256
* ALPN, server accepted to use http/1.1
* Server certificate:
* subject: CN=test.example.com
* start date: Nov 11 00:00:00 2018 GMT
* expire date: Dec 11 12:00:00 2019 GMT
* subjectAltName does not match xxxx.us-east-1.elb.amazonaws.com
* SSL: no alternative certificate subject name matches target host name 'xxxx.us-east-1.elb.amazonaws.com'
* Closing connection 0
* TLSv1.2 (OUT), TLS alert, Client hello (1):
curl: (51) SSL: no alternative certificate subject name matches target host name 'xxxx.us-east-1.elb.amazonaws.com'

Python Requests:

Code:

import requests

url = "https://xxxxx.us-east-1.elb.amazonaws.com/prod/testapi"

payload = ""paras1": "xxxxx""
headers = 
 'Content-Type': "application/json",
 'cache-control': "no-cache"
 

response = requests.request("POST", url, data=payload, headers=headers)

print(response.text)

Error:

HTTPSConnectionPool(host='xxxx.us-east-1.elb.amazonaws.com', port=443): 
Max retries exceeded with url: /prod/testapi 
(Caused by SSLError(CertificateError("hostname 'xxxx.us-east-1.elb.amazonaws.com' doesn't match 'test.example.com'",),))

I can use the DNS of ALB (xxxx.us-east-1.elb.amazonaws.com)

That isn't how this is designed to work. You need to point test.example.com to the ELB in DNS, and then:

url = "https://test.example.com/prod/testapi"

Clearly, you call xxxx.us-east-1.elb.amazonaws.com which is set up with a certificate for test.example.com. Despite the certificate may be valid it does not match the URL you are calling which means that the certificate is NOT valid for THIS call. I think you also must set a custom domain for the API gateway. https://docs.aws.amazon.com/apigateway/latest/developerguide/how-to-custom-domains.html

Edit: thanks for the comment. I am not sure how I read "elb" as an api gateway. My fault. Still the DNS for the ELB has to match the one in the certificat. You can create a CNAME from your domain to the ELB domain. This should work (at least this is how we do that).