Syntax Properties Return values Examples

AWS::EC2::FlowLog

Specifies an Amazon Elastic Compute Cloud (Amazon EC2) flow log that captures IP traffic for a specified network interface, subnet, or VPC. To view the log data, use Amazon CloudWatch Logs (CloudWatch Logs) to help troubleshoot connection issues. For example, you can use a flow log to investigate why certain traffic isn't reaching an instance, which can help you diagnose overly restrictive security group rules. For more information, see VPC Flow Logs in the Amazon VPC User Guide.

Syntax

To declare this entity in your AWS CloudFormation template, use the following syntax:

JSON


{
  "Type" : "AWS::EC2::FlowLog",
  "Properties" : {
      "DeliverLogsPermissionArn" : String,
      "LogDestination" : String,
      "LogDestinationType" : String,
      "LogFormat" : String,
      "LogGroupName" : String,
      "MaxAggregationInterval" : Integer,
      "ResourceId" : String,
      "ResourceType" : String,
      "Tags" : [ Tag, ... ],
      "TrafficType" : String
    }
}

YAML


Type: AWS::EC2::FlowLog
Properties: 
  DeliverLogsPermissionArn: String
  LogDestination: String
  LogDestinationType: String
  LogFormat: String
  LogGroupName: String
  MaxAggregationInterval: Integer
  ResourceId: String
  ResourceType: String
  Tags: 
    - Tag
  TrafficType: String

Properties

DeliverLogsPermissionArn

The ARN for the IAM role that permits Amazon EC2 to publish flow logs to a CloudWatch Logs log group in your account.

If you specify LogDestinationType as s3, do not specify DeliverLogsPermissionArn or LogGroupName.

Required: No

Type: String

Update requires: Replacement

LogDestination

Specifies the destination to which the flow log data is to be published. Flow log data can be published to a CloudWatch Logs log group or an Amazon S3 bucket. The value specified for this parameter depends on the value specified for LogDestinationType.

If LogDestinationType is not specified or cloud-watch-logs, specify the Amazon Resource Name (ARN) of the CloudWatch Logs log group. For example, to publish to a log group called my-logs, specify arn:aws:logs:us-east-1:123456789012:log-group:my-logs. Alternatively, use LogGroupName instead.

If LogDestinationType is s3, specify the ARN of the Amazon S3 bucket. You can also specify a subfolder in the bucket. To specify a subfolder in the bucket, use the following ARN format: bucket_ARN/subfolder_name/. For example, to specify a subfolder named my-logs in a bucket named my-bucket, use the following ARN: arn:aws:s3:::my-bucket/my-logs/. You cannot use AWSLogs as a subfolder name. This is a reserved term.

Required: No

Type: String

Update requires: Replacement

LogDestinationType

Specifies the type of destination to which the flow log data is to be published. Flow log data can be published to CloudWatch Logs or Amazon S3. To publish flow log data to CloudWatch Logs, specify cloud-watch-logs. To publish flow log data to Amazon S3, specify s3.

If you specify LogDestinationType as s3, do not specify DeliverLogsPermissionArn or LogGroupName.

Default: cloud-watch-logs

Required: No

Type: String

Allowed values: cloud-watch-logs | s3

Update requires: Replacement

LogFormat

The fields to include in the flow log record, in the order in which they should appear. For a list of available fields, see Flow Log Records. If you omit this parameter, the flow log is created using the default format. If you specify this parameter, you must specify at least one field.

Specify the fields using the ${field-id} format, separated by spaces.

Required: No

Type: String

Update requires: Replacement

LogGroupName

The name of a new or existing CloudWatch Logs log group where Amazon EC2 publishes your flow logs.

If you specify LogDestinationType as s3, do not specify DeliverLogsPermissionArn or LogGroupName.

Required: No

Type: String

Update requires: Replacement

MaxAggregationInterval

The maximum interval of time during which a flow of packets is captured and aggregated into a flow log record. You can specify 60 seconds (1 minute) or 600 seconds (10 minutes).

When a network interface is attached to a Nitro-based instance, the aggregation interval is always 60 seconds or less, regardless of the value that you specify.

Default: 600

Required: No

Type: Integer

Update requires: Replacement

ResourceId

The ID of the subnet, network interface, or VPC for which you want to create a flow log.

Required: Yes

Type: String

Update requires: Replacement

ResourceType

The type of resource for which to create the flow log. For example, if you specified a VPC ID for the ResourceId property, specify VPC for this property.

Required: Yes

Type: String

Allowed values: NetworkInterface | Subnet | VPC

Update requires: Replacement

Tags

The tags for the flow log.

Required: No

Type: List of Tag

Update requires: No interruption

TrafficType

The type of traffic to log. You can log traffic that the resource accepts or rejects, or all traffic.

Required: Yes

Type: String

Allowed values: ACCEPT | ALL | REJECT

Update requires: Replacement

Return values

Ref

When you pass the logical ID of this resource to the intrinsic Ref function, Ref returns the flow log ID, such as fl-123456abc123abc1.

For more information about using the Ref function, see Ref.

Fn::GetAtt

The Fn::GetAtt intrinsic function returns a value for a specified attribute of this type. The following are the available attributes and sample return values.

For more information about using the Fn::GetAtt intrinsic function, see Fn::GetAtt.

Id: The ID of the flow log. For example, fl-123456abc123abc1.

Examples

Publish a flow log to CloudWatch Logs to monitor all traffic

The following example creates a flow log for the specified VPC, and captures all traffic types. Amazon EC2 publishes the logs to the FlowLogsGroup log group.

JSON


{
  "MyFlowLog": {
    "Type": "AWS::EC2::FlowLog",
    "Properties": {
      "DeliverLogsPermissionArn": {
        "Fn::GetAtt": [
          "FlowLogRole",
          "Arn"
        ]
      },
      "LogGroupName": "FlowLogsGroup",
      "ResourceId": {
        "Ref": "MyVPC"
      },
      "ResourceType": "VPC",
      "TrafficType": "ALL"
    }
  }
}

YAML


MyFlowLog:
  Type: AWS::EC2::FlowLog
  Properties:
    DeliverLogsPermissionArn: !GetAtt FlowLogRole.Arn
    LogGroupName: FlowLogsGroup
    ResourceId: !Ref MyVPC
    ResourceType: VPC
    TrafficType: ALL

Publish a custom format flow log to CloudWatch Logs for REJECT traffic

The following example creates a flow log for the specified subnet and captures REJECT traffic. The flow log uses a custom log format (the LogFormat property uses the ${field-id} format, separated by spaces). Amazon EC2 aggregates the logs over 60 second intervals, and publishes the logs to the FlowLogsGroup log group. The flow log is created with two tags.

JSON


{
  "MyDetailedFlowLogDeliveringToCloudWatchLogs": {
    "Type": "AWS::EC2::FlowLog",
    "Properties": {
      "ResourceId": {
        "Ref": "MySubnet"
      },
      "ResourceType": "Subnet",
      "TrafficType": "REJECT",
      "LogGroupName": "FlowLogsGroup",
      "DeliverLogsPermissionArn": {
        "Fn::GetAtt": [
          "FlowLogRole",
          "Arn"
        ]
      },
      "LogFormat": "${version} ${vpc-id} ${subnet-id} ${instance-id} ${srcaddr} ${dstaddr} ${srcport} ${dstport} ${protocol} ${tcp-flags} ${type} ${pkt-srcaddr} ${pkt-dstaddr}",
      "MaxAggregationInterval": 60,
      "Tags": [
        {
          "Key": "Name",
          "Value": "FlowLogForSubnetA"
        },
        {
          "Key": "Purpose",
          "Value": "RejectTraffic"
        }
      ]
    }
  }
}

YAML


MyDetailedFlowLogDeliveringToCloudWatchLogs:
  Type: AWS::EC2::FlowLog
  Properties: 
    ResourceId: !Ref MySubnet
    ResourceType: Subnet
    TrafficType: REJECT
    LogGroupName: FlowLogsGroup
    DeliverLogsPermissionArn: !GetAtt FlowLogRole.Arn
    LogFormat: '${version} ${vpc-id} ${subnet-id} ${instance-id} ${srcaddr} ${dstaddr} ${srcport} ${dstport} ${protocol} ${tcp-flags} ${type} ${pkt-srcaddr} ${pkt-dstaddr}'
    MaxAggregationInterval: 60
    Tags:
      -
        Key: Name
        Value: FlowLogForSubnetA
      -
        Key: Purpose
        Value: RejectTraffic

Publish a custom format flow log to Amazon S3 for ACCEPT traffic

The following example creates a flow log for the specified subnet and captures ACCEPT traffic. The flow log uses a custom log format (the LogFormat property uses the ${field-id} format, separated by spaces). Amazon EC2 aggregates the logs over 60 second intervals, and publishes the logs to an Amazon S3 bucket that's referenced by its ARN, MyS3Bucket.Arn. The flow log is created with two tags.

JSON


{
  "MyFlowLogDeliveringToS3": {
    "Type": "AWS::EC2::FlowLog",
    "Properties": {
      "ResourceId": {
        "Ref": "MySubnet"
      },
      "ResourceType": "Subnet",
      "TrafficType": "ACCEPT",
      "LogDestination": {
        "Fn::GetAtt": [
          "MyS3Bucket",
          "Arn"
        ]
      },
      "LogDestinationType": "s3",
      "LogFormat": "${version} ${vpc-id} ${subnet-id} ${instance-id} ${srcaddr} ${dstaddr} ${srcport} ${dstport} ${protocol} ${tcp-flags} ${type} ${pkt-srcaddr} ${pkt-dstaddr}",
      "MaxAggregationInterval": 60,
      "Tags": [
        {
          "Key": "Name",
          "Value": "FlowLogForSubnetB"
        },
        {
          "Key": "Purpose",
          "Value": "AcceptTraffic"
        }
      ]
    }
  }
}

YAML


MyFlowLogDeliveringToS3:
  Type: AWS::EC2::FlowLog
  Properties: 
    ResourceId: !Ref MySubnet
    ResourceType: Subnet
    TrafficType: ACCEPT
    LogDestination: !GetAtt MyS3Bucket.Arn
    LogDestinationType: s3
    LogFormat: '${version} ${vpc-id} ${subnet-id} ${instance-id} ${srcaddr} ${dstaddr} ${srcport} ${dstport} ${protocol} ${tcp-flags} ${type} ${pkt-srcaddr} ${pkt-dstaddr}'
    MaxAggregationInterval: 60
    Tags:
      -
        Key: Name
        Value: FlowLogForSubnetB
      -
        Key: Purpose
        Value: AcceptTraffic

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Document Conventions

AWS::EC2::EIPAssociation

AWS::EC2::GatewayRouteTableAssociation