Sending AWS Network Firewall logs to Amazon Simple Storage Service

To send your firewall logs to Amazon S3, you need to set up an Amazon S3 bucket as the destination for the logs. In your bucket configuration for the firewall, you can optionally include a prefix, to immediately follow the bucket name. When you enable logging to Amazon S3 in Network Firewall, you provide the bucket name and, if you are using one, the prefix. For information about creating your logging bucket, see Create a Bucket in the Amazon Simple Storage Service User Guide.

Note

Network Firewall supports encryption with Amazon S3 buckets for key type Amazon S3 key (SSE-S3) and for AWS Key Management Service (SSE-KMS) AWS KMS keys. Network Firewall doesn't support encryption for AWS Key Management Service keys that are managed by AWS.

Network Firewall collects log records, consolidates them into log files, and then publishes the log files to the Amazon S3 bucket at 5-minute intervals. Each log file contains log records for the network traffic recorded in the previous five minutes.

The maximum file size for a log file is 75 MB. If the log file reaches the file size limit within the 5-minute period, the log stops adding records to it, publishes it to the Amazon S3 bucket, and then creates a new log file.

A single log file contains interleaved entries with multiple connection identifier (source IP address, source port, destination IP address, destination port, and protocol) records. To see all the log files for your firewall, look for entries aggregated by the firewall name and your account ID.

Log files are saved in the specified Amazon S3 bucket using a folder structure that's determined by the log's ID, Region, Network Firewall log type, and the date. The bucket folder structure uses the following format:

s3-bucket-name/optional-s3-bucket-prefix/AWSLogs/aws-account-id/network-firewall/log-type/Region/firewall-name/timestamp/

Similarly, the log file name is determined by the flow log's ID, Region, and the date and time it was created. File names use the following format:

aws-account-id_network-firewall_log-type_Region_firewall-name_timestamp_hash.log.gz

In the specification of the folder and file name, the following apply:

• The log type is either alert, flow, or tls.

• The timestamp uses the YYYYMMDDTHHmmZ format.

• If you don't provide a specification for the S3 bucket prefix, the log file bucket folder structure will be similar to the following:

  s3-bucket-name/AWSLogs/aws-account-id

• If you specify slash (/) for the S3 bucket prefix, or provide a prefix that begins with a slash, the log file bucket folder structure will contain a double slash (//), like the following for a prefix set to a single slash:

  s3-bucket-name//AWSLogs/aws-account-id

The following shows an example flow log file in Amazon S3 for AWS account 11111111111, firewall name test-firewall, bucket name s3://amzn-s3-demo-bucket, and bucket prefix flow-logs.

s3://amzn-s3-demo-bucket/flow-logs/AWSLogs/11111111111/network-firewall/flow/us-east-1/test-firewall/2020/10/01/19/11111111111_network-firewall_flow_us-east-1_test-firewall_202010011920_44442222.log.gz

Permissions to publish logs to Amazon S3

You must have the following permissions settings to configure your firewall to send logs to Amazon S3.

{
    "Version": "2012-10-17",
    "Statement": [
        {
            "Action": [
                "logs:CreateLogDelivery",
                "logs:GetLogDelivery",
                "logs:UpdateLogDelivery",
                "logs:DeleteLogDelivery",
                "logs:ListLogDeliveries"
            ],
            "Resource": [
                "*"
            ],
            "Effect": "Allow",
            "Sid": "FirewallLogging"
        },
        {
            "Sid": "FirewallLoggingS3",
            "Action": [
                "s3:PutBucketPolicy",
                "s3:GetBucketPolicy"
            ],
            "Resource": [
                Amazon S3 bucket ARN"
            ],
            "Effect": "Allow"
        }
    ]
}

By default, Amazon S3 buckets and the objects that they contain are private. Only the bucket owner can access the bucket and the objects stored in it. The bucket owner, however, can grant access to other resources and users by writing an access policy.

If the user creating the log owns the bucket, the service automatically attaches the following policy to the bucket to give the log permission to publish logs to it:

{
    "Version": "2012-10-17",
    "Statement": [
        {
            "Sid": "AWSLogDeliveryWrite",
            "Effect": "Allow",
            "Principal": {"Service": "delivery.logs.amazonaws.com"},
            "Action": "s3:PutObject",
            "Resource": "arn:aws:s3:::bucket-name/optional-folder/AWSLogs/account-id/*",
            "Condition": {"StringEquals": {"s3:x-amz-acl": "bucket-owner-full-control"}}
        },
        {
            "Sid": "AWSLogDeliveryAclCheck",
            "Effect": "Allow",
            "Principal": {"Service": "delivery.logs.amazonaws.com"},
            "Action": "s3:GetBucketAcl",
            "Resource": "arn:aws:s3:::bucket-name"
        }
    ]
}

If the user creating the log doesn't own the bucket, or doesn't have the GetBucketPolicy and PutBucketPolicy permissions for the bucket, the log creation fails. In this case, the bucket owner must manually add the preceding policy to the bucket and specify the log creator's AWS account ID. For more information, see How Do I Add an S3 Bucket Policy? in the Amazon Simple Storage Service User Guide. If the bucket receives logs from multiple accounts, add a Resource element entry to the AWSLogDeliveryWrite policy statement for each account.

For example, the following bucket policy allows AWS accounts 111122223333 and 444455556666 to publish logs to a folder named flow-logs in a bucket named amzn-s3-demo-bucket:

{
    "Version": "2012-10-17",
    "Statement": [
        {
            "Sid": "AWSLogDeliveryWrite",
            "Effect": "Allow",
            "Principal": {"Service": "delivery.logs.amazonaws.com"},
            "Action": "s3:PutObject",
            "Resource": [
            	"arn:aws:s3:::amzn-s3-demo-bucket:/flow-logs/AWSLogs/111122223333/",
            	"arn:aws:s3:::amzn-s3-demo-bucket:/flow-logs/AWSLogs/444455556666/"
            	],
            "Condition": {"StringEquals": {"s3:x-amz-acl": "bucket-owner-full-control"}}
        },
        {
            "Sid": "AWSLogDeliveryAclCheck",
            "Effect": "Allow",
            "Principal": {"Service": "delivery.logs.amazonaws.com"},
            "Action": "s3:GetBucketAcl",
            "Resource": "arn:aws:s3:::amzn-s3-demo-bucket"
        }
    ]
}

Amazon S3 log file access

In addition to the required bucket policies, Amazon S3 uses access control lists (ACLs) to manage access to the log files created by a Network Firewall log. By default, the bucket owner has FULL_CONTROL permissions on each log file. The log delivery owner, if different from the bucket owner, has no permissions. The log delivery account has READ and WRITE permissions. For more information, see Access Control List (ACL) Overview in the Amazon Simple Storage Service User Guide.

The log files are compressed. If you open the files using the Amazon S3 console, Amazon S3 decompresses the log records and displays them. If you download the log files, you must decompress them to view the records.