将SSL证书上传到AWS Elastic Load Balancer

The AWS CLI uses a provider chain to look for AWS credentials in a number of different places, including system or user environment variables and local AWS configuration files.

http://docs.aws.amazon.com/cli/latest/userguide/cli-chap-getting-started.html

Although it's hard to guess the specific local machine configuration issue that resulted in the behavior observed, as noted in the comments, this appeared to be an issue where aws cli was using two different sets of credentials to access two different services, and these two sets of credentials were actually from two different AWS accounts.

The ServerCertificateName returned by the API (accessed through the CLI) should have matched the certificate name shown in the console drop-down for Elastic Load Balancer certificate selection.

The composition of ARNs (Amazon Resource Names) varies by service, but often includes the AWS account number. In this case, the account number shown in the CLI output did not match what was visible in the AWS console... leading to the conclusion that the issue was that an AWS account other than the intended one was being accessed by aws cli.

As cross-confirmed by the differing display names, the "existing" certificate, uploaded a year ago, may have had the same content but was in fact a different IAM entity than the one seen in the dropdown, as the two certificates were associated with entirely different accounts.