As we learned in the previous chapter, AWS provides a wide variety of tools and managed services which allow you to safeguard your applications running on the cloud, such as AWS WAF and AWS Shield. But this, however, just forms one important piece in a much larger jigsaw puzzle! What about compliance monitoring, risk auditing, and overall governance of your environments? How do you effectively analyze events occurring in your environment and mitigate against the same? Well, luckily for us, AWS has the answer to our problems in the form of AWS CloudTrail.

AWS CloudTrail provides you with the ability to log every single action taken by a user, service, role, or even API, from within your AWS account. Each action recorded is treated as an event which can then be analyzed for enhancing the security of your AWS environment. The following are some of the key benefits that you can obtain by enabling CloudTrail for your AWS accounts:

• In-depth visibility: Using CloudTrail, you can easily gain better insights into your account's usage by recording each user's activities, such as which user initiated a new resource creation, from which IP address was this request initiated, which resources were created and at what time, and much more!
• Easier compliance monitoring: With CloudTrail, you can easily record and log events occurring within your AWS account, whether they may originate from the Management Console, or the AWS CLI, or even from other AWS tools and services. The best thing about this is that you can integrate CloudTrail with another AWS service, such as Amazon CloudWatch, to alert and respond to out-of-compliance events.
• Security automations: As we saw in the previous chapter, automating responses to security threats not only enables you to mitigate the potential threats faster, but also provides you with a mechanism to stop all further attacks. The same can be applied to AWS CloudTrail as well! With its easy integration with Amazon CloudWatch events, you can now create corresponding Lambda functions that trigger automatically each time a compliance is not met, all in a matter of seconds!

With these key points in mind, let's have a quick look at some of CloudTrail's essential concepts and terminologies:

• Events: Events are the basic unit of measurement in CloudTrail. Essentially, an event is nothing more than a record of a particular activity either initiated by the AWS services, roles, or even an AWS user. These activities are all logged as API calls that can originate from the Management Console, the AWS SDK, or even the AWS CLI as well. By default, events are stored by CloudTrail with S3 buckets for a period of 7 days. You can view, search, and even download these events by leveraging the events history feature provided by CloudTrail.
• Trails: Trails are essentially the delivery mechanism, using which events are dumped to S3 buckets. You can use these trails to log specific events within specific buckets, as well as to filter events and encrypt the transmitted log files. By default, you can have a maximum of five trails created per AWS region, and this limit cannot by increased.
• CloudTrail Logs: Once your CloudTrail starts capturing events, it sends these events to an S3 bucket in the form of a CloudTrail Log file. The log files are JSON text files that are compressed using the .gzip format. Each file can contain one or more events within itself. Here is a simple representation of what a CloudTrail Log looks like. In this case, the event was created when I tried to add an existing user by the name of Mike to an administrator group using the AWS Management Console:

{"Records": [{ 
    "eventVersion": "1.0", 
    "userIdentity": { 
        "type": "IAMUser", 
        "principalId": "12345678", 
        "arn": "arn:aws:iam::012345678910:user/yohan", 
        "accountId": "012345678910", 
        "accessKeyId": "AA34FG67GH89", 
        "userName": "Alice", 
        "sessionContext": {"attributes": { 
            "mfaAuthenticated": "false", 
            "creationDate": "2017-11-08T13:01:44Z" 
        }} 
    }, 
    "eventTime": "2017-11-08T13:09:44Z", 
    "eventSource": "iam.amazonaws.com", 
    "eventName": "AddUserToGroup", 
    "awsRegion": "us-east-1", 
    "sourceIPAddress": "127.0.0.1", 
    "userAgent": "AWSConsole", 
    "requestParameters": { 
        "userName": "Mike", 
        "groupName": "administrator" 
    }, 
    "responseElements": null 
}]} 

You can view your own CloudTrail Log files by visiting the S3 bucket that you specify during the trail's creation. Each log file is named uniquely using the following format:

AccountID_CloudTrail_RegionName_YYYYMMDDTHHmmZ_UniqueString.json.gz 

Where:

• AccountID: Your AWS account ID.
• RegionName: AWS region where the event was captured: us-east-1, and so on.
• YYYYMMDDTTHHmmz: Specifies the year, month, day, hour (24 hours), minutes, and seconds. The z indicates time in UTC.
• UniqueString: A randomly generated 16-character-long string that is simply used so that there is no overwriting of the log files.

With the basics in mind, let's quickly have a look at how you can get started with CloudTrail for your own AWS environments!