SSL certificates for your Application Load Balancer
When you create a secure listener for your Application Load Balancer, you must deploy at least one certificate on the load balancer. The load balancer requires X.509 certificates (SSL/TLS server certificates). Certificates are a digital form of identification issued by a certificate authority (CA). A certificate contains identification information, a validity period, a public key, a serial number, and the digital signature of the issuer.
When you create a certificate for use with your load balancer, you must specify a domain name. The domain name on the certificate must match the custom domain name record so that we can verify the TLS connection. If they do not match, the traffic is not encrypted.
You must specify a fully qualified domain name (FQDN) for your certificate, such as
www.example.com or an apex domain name such as example.com.
You can also use an asterisk (*) as a wild card to protect several site names in the
same domain. When you request a wild-card certificate, the asterisk (*) must be in the
leftmost position of the domain name and can protect only one subdomain level. For
instance, *.example.com protects corp.example.com, and
images.example.com, but it cannot protect test.login.example.com.
Also note that *.example.com protects only the subdomains of
example.com, it does not protect the bare or apex domain (example.com).
The wild-card name appears in the Subject field and in the
Subject Alternative Name extension of the certificate. For more
information about public certificates, see Requesting a public certificate in the AWS Certificate Manager User Guide.
We recommend that you create certificates for your load balancer using AWS Certificate Manager (ACM)
Alternatively, you can use SSL/TLS tools to create a certificate signing request (CSR), then get the CSR signed by a CA to produce a certificate, then import the certificate into ACM or upload the certificate to AWS Identity and Access Management (IAM). For more information about importing certificates into ACM, see Importing certificates in the AWS Certificate Manager User Guide. For more information about uploading certificates to IAM, see Working with server certificates in the IAM User Guide.
Default certificate
When you create an HTTPS listener, you must specify exactly one certificate. This certificate is known as the default certificate. You can replace the default certificate after you create the HTTPS listener. For more information, see Replace the default certificate.
If you specify additional certificates in a certificate list, the default certificate is used only if a client connects without using the Server Name Indication (SNI) protocol to specify a hostname or if there are no matching certificates in the certificate list.
If you do not specify additional certificates but need to host multiple secure applications through a single load balancer, you can use a wildcard certificate or add a Subject Alternative Name (SAN) for each additional domain to your certificate.
Certificate list
After you create an HTTPS listener, it has a default certificate and an empty certificate list. You can optionally add certificates to the certificate list for the listener. Using a certificate list enables the load balancer to support multiple domains on the same port and provide a different certificate for each domain. For more information, see Add certificates to the certificate list.
The load balancer uses a smart certificate selection algorithm with support for SNI. If the hostname provided by a client matches a single certificate in the certificate list, the load balancer selects this certificate. If a hostname provided by a client matches multiple certificates in the certificate list, the load balancer selects the best certificate that the client can support. Certificate selection is based on the following criteria in the following order:
-
Public key algorithm (prefer ECDSA over RSA)
-
Hashing algorithm (prefer SHA over MD5)
-
Key length (prefer the largest)
-
Validity period
The load balancer access log entries indicate the hostname specified by the client and the certificate presented to the client. For more information, see Access log entries.
Certificate renewal
Each certificate comes with a validity period. You must ensure that you renew or replace each certificate for your load balancer before its validity period ends. This includes the default certificate and certificates in a certificate list. Renewing or replacing a certificate does not affect in-flight requests that were received by the load balancer node and are pending routing to a healthy target. After a certificate is renewed, new requests use the renewed certificate. After a certificate is replaced, new requests use the new certificate.
You can manage certificate renewal and replacement as follows:
-
Certificates provided by AWS Certificate Manager and deployed on your load balancer can be renewed automatically. ACM attempts to renew certificates before they expire. For more information, see Managed renewal in the AWS Certificate Manager User Guide.
-
If you imported a certificate into ACM, you must monitor the expiration date of the certificate and renew it before it expires. For more information, see Importing certificates in the AWS Certificate Manager User Guide.
-
If you imported a certificate into IAM, you must create a new certificate, import the new certificate to ACM or IAM, add the new certificate to your load balancer, and remove the expired certificate from your load balancer.
