# FlowLog

A VPC flow log.

Extends: Construct › Resource › FlowLog
Implements: IResource, IFlowLog, IEnvironmentAware, IFlowLogRef, IConstruct, IDependable

- CloudFormation: [`AWS::EC2::FlowLog`](https://docs.aws.amazon.com/AWSCloudFormation/latest/TemplateReference/aws-resource-ec2-flowlog.html)
- L1 type: [`CfnFlowLog`](/cdk/api/v2/docs/aws-cdk-lib.aws_ec2.CfnFlowLog.html)
- Source: [`aws-ec2/lib/vpc-flow-logs.ts`](https://github.com/aws/aws-cdk/blob/v2.275.0/packages/aws-cdk-lib/aws-ec2/lib/vpc-flow-logs.ts#L863)
- Type last changed: v2.238.0 · 9 Feb 2026

## Example

```ts
declare const tgw: ec2.CfnTransitGateway;

new ec2.FlowLog(this, 'TransitGatewayFlowLog', {
  resourceType: ec2.FlowLogResourceType.fromTransitGatewayId(tgw.ref)
})
```

## Initializer

```ts
new FlowLog(scope: Construct, id: string, props: FlowLogProps)
```

## Construct Props

- `destination`: [FlowLogDestination](/cdk/api/v2/docs/aws-cdk-lib.aws_ec2.FlowLogDestination.html) — Specifies the type of destination to which the flow log data is to be published.

  **Default:** FlowLogDestinationType.toCloudWatchLogs()

  Flow log data can be published to CloudWatch Logs or Amazon S3

- `flowLogName`: string — The name of the FlowLog.

  **Default:** CDK generated name

  Since the FlowLog resource doesn't support providing a physical name, the value provided here will be recorded in the `Name` tag.

- `logFormat`: [LogFormat](/cdk/api/v2/docs/aws-cdk-lib.aws_ec2.LogFormat.html)[] — The fields to include in the flow log record, in the order in which they should appear.

  **Default:** default log format is used.

  If multiple fields are specified, they will be separated by spaces. For full control over the literal log format
  string, pass a single field constructed with `LogFormat.custom()`.

  See https://docs.aws.amazon.com/vpc/latest/userguide/flow-logs.html#flow-log-records

- `maxAggregationInterval`: [FlowLogMaxAggregationInterval](/cdk/api/v2/docs/aws-cdk-lib.aws_ec2.FlowLogMaxAggregationInterval.html) — The maximum interval of time during which a flow of packets is captured and aggregated into a flow log record.

  **Default:** FlowLogMaxAggregationInterval.ONE_MINUTES if creating flow logs for Transit Gateway, otherwise FlowLogMaxAggregationInterval.TEN_MINUTES.

  When creating flow logs for a Transit Gateway or Transit Gateway Attachment,
  this property must be ONE_MINUTES.

- `resourceType`: [FlowLogResourceType](/cdk/api/v2/docs/aws-cdk-lib.aws_ec2.FlowLogResourceType.html) (required) — The type of resource for which to create the flow log.

- `trafficType`: [FlowLogTrafficType](/cdk/api/v2/docs/aws-cdk-lib.aws_ec2.FlowLogTrafficType.html) = ALL — The type of traffic to log.

  You can log traffic that the resource accepts or rejects, or all traffic.
  When the target is either `TransitGateway` or `TransitGatewayAttachment`, setting the traffic type is not possible.

## Properties

- `bucket`: [IBucket](/cdk/api/v2/docs/aws-cdk-lib.aws_s3.IBucket.html) — The S3 bucket to publish flow logs to.

- `deliveryStream`: [IDeliveryStreamRef](/cdk/api/v2/docs/aws-cdk-lib.interfaces.aws_kinesisfirehose.IDeliveryStreamRef.html) — The Amazon Data Firehose delivery stream to publish flow logs to.

- `deliveryStreamArn`: string — Use deliveryStream

- `env`: [ResourceEnvironment](/cdk/api/v2/docs/aws-cdk-lib.interfaces.ResourceEnvironment.html) — The environment this resource belongs to.

  For resources that are created and managed in a Stack (those created by
  creating new class instances like `new Role()`, `new Bucket()`, etc.), this
  is always the same as the environment of the stack they belong to.

  For referenced resources (those obtained from referencing methods like
  `Role.fromRoleArn()`, `Bucket.fromBucketName()`, etc.), they might be
  different than the stack they were imported into.

- `flowLogId`: string — The Id of the VPC Flow Log.

- `flowLogRef`: [FlowLogReference](/cdk/api/v2/docs/aws-cdk-lib.interfaces.aws_ec2.FlowLogReference.html) — A reference to a FlowLog resource.

- `iamRole`: [IRole](/cdk/api/v2/docs/aws-cdk-lib.aws_iam.IRole.html) — The iam role used to publish logs to CloudWatch.

- `keyPrefix`: string — S3 bucket key prefix to publish the flow logs under.

- `logGroup`: [ILogGroup](/cdk/api/v2/docs/aws-cdk-lib.aws_logs.ILogGroup.html) — The CloudWatch Logs LogGroup to publish flow logs to.

- `node`: [Node](/cdk/api/v2/docs/constructs.Node.html) — The tree node.

- `PROPERTY_INJECTION_ID`: string (static) — Uniquely identifies this class.

- `stack`: [Stack](/cdk/api/v2/docs/aws-cdk-lib.Stack.html) — The stack in which this resource is defined.

## Methods

- `applyCrossStackReferenceStrength(strength: ReferenceStrength): void` — Override the cross-stack reference strength for this resource.

  When set, any cross-stack reference to this resource will use the specified
  mechanism instead of the global default determined by the
  `@aws-cdk/core:defaultCrossStackReferences` context key. This is useful for
  selectively weakening specific references to avoid the "deadly embrace" problem
  without changing the app-wide default.

  **Parameters**

  - `strength` — - The reference strength to use for this resource.

- `applyRemovalPolicy(policy: RemovalPolicy): void` — Apply the given removal policy to this resource.

  The Removal Policy controls what happens to this resource when it stops
  being managed by CloudFormation, either because you've removed it from the
  CDK application or because you've made a change that requires the resource
  to be replaced.

  The resource can be deleted (`RemovalPolicy.DESTROY`), or left in your AWS
  account for data recovery and cleanup later (`RemovalPolicy.RETAIN`).

- `fromFlowLogId(scope: Construct, id: string, flowLogId: string): IFlowLog` (static) — Import a Flow Log by it's Id.

- `isConstruct(x: any): boolean` (static) — Checks if `x` is a construct.

  Use this method instead of `instanceof` to properly detect `Construct`
  instances, even when the construct library is symlinked.

  Explanation: in JavaScript, multiple copies of the `constructs` library on
  disk are seen as independent, completely different libraries. As a
  consequence, the class `Construct` in each copy of the `constructs` library
  is seen as a different class, and an instance of one class will not test as
  `instanceof` the other class. `npm install` will not create installations
  like this, but users may manually symlink construct libraries together or
  use a monorepo tool: in those cases, multiple copies of the `constructs`
  library can be accidentally installed, and `instanceof` will behave
  unpredictably. It is safest to avoid using `instanceof`, and using
  this type-testing method instead.

  **Parameters**

  - `x` — Any object.

  **Returns:** true if `x` is an object created from a class which extends `Construct`.

- `isOwnedResource(construct: IConstruct): boolean` (static) — Returns true if the construct was created by CDK, and false otherwise.

- `isResource(construct: IConstruct): boolean` (static) — Check whether the given construct is a Resource.

- `toString(): string` — Returns a string representation of this construct.

- `with(...mixins: IMixin[]): IConstruct` — Applies one or more mixins to this construct.

  Mixins are applied in order. The list of constructs is captured at the
  start of the call, so constructs added by a mixin will not be visited.
  Use multiple `with()` calls if subsequent mixins should apply to added
  constructs.