**To add a source identifier to a subscription**

This example adds another source identifier to an existing subscription::

    aws rds add-source-identifier-to-subscription \
    --subscription-name my-instance-events \
    --source-identifier test-instance-repl

Output::

{
    "EventSubscription": {
        "SubscriptionCreationTime": "Tue Jul 31 23:22:01 UTC 2018",
        "CustSubscriptionId": "my-instance-events",
        "EventSubscriptionArn": "arn:aws:rds:us-east-1:123456789012:es:my-instance-events",
        "Enabled": false,
        "Status": "modifying",
        "EventCategoriesList": [
            "backup",
            "recovery"
        ],
        "CustomerAwsId": "123456789012",
        "SnsTopicArn": "arn:aws:sns:us-east-1:123456789012:interesting-events",
        "SourceType": "db-instance",
        "SourceIdsList": [
            "test-instance",
            "test-instance-repl"
        ]
    }
}