# XffHeaderProcessingMode

Processing mode of the X-Forwarded-For header in the HTTP request before the Application Load Balancer sends the request to the target.

- Source: [`aws-elasticloadbalancingv2/lib/alb/application-load-balancer.ts`](https://github.com/aws/aws-cdk/blob/v2.275.0/packages/aws-cdk-lib/aws-elasticloadbalancingv2/lib/alb/application-load-balancer.ts#L135)
- Type last changed: v2.137.0 · 11 Apr 2024

## Example

```ts
declare const vpc: ec2.Vpc;

const lb = new elbv2.ApplicationLoadBalancer(this, 'LB', {
  vpc,
  internetFacing: true,

  // Whether HTTP/2 is enabled
  http2Enabled: false,

  // The idle timeout value, in seconds
  idleTimeout: Duration.seconds(1000),

  // Whether HTTP headers with header fields that are not valid
  // are removed by the load balancer (true), or routed to targets
  dropInvalidHeaderFields: true,

  // How the load balancer handles requests that might
  // pose a security risk to your application
  desyncMitigationMode: elbv2.DesyncMitigationMode.DEFENSIVE,

  // The type of IP addresses to use.
  ipAddressType: elbv2.IpAddressType.IPV4,

  // The duration of client keep-alive connections
  clientKeepAlive: Duration.seconds(500),

  // Whether cross-zone load balancing is enabled.
  crossZoneEnabled: true,

  // Whether the load balancer blocks traffic through the Internet Gateway (IGW).
  denyAllIgwTraffic: false,

  // Whether to preserve host header in the request to the target
  preserveHostHeader: true,

  // Whether to add the TLS information header to the request
  xAmznTlsVersionAndCipherSuiteHeaders: true,

  // Whether the X-Forwarded-For header should preserve the source port
  preserveXffClientPort: true,

  // The processing mode for X-Forwarded-For headers
  xffHeaderProcessingMode: elbv2.XffHeaderProcessingMode.APPEND,

  // Whether to allow a load balancer to route requests to targets if it is unable to forward the request to AWS WAF.
  wafFailOpen: true,
});
```

## Members

| Member | Description |
| --- | --- |
| `APPEND` | Application Load Balancer adds the client IP address (of the last hop) to the X-Forwarded-For header in the HTTP request before it sends it to targets. |
| `PRESERVE` | Application Load Balancer preserves the X-Forwarded-For header in the HTTP request, and sends it to targets without any change. |
| `REMOVE` | Application Load Balancer removes the X-Forwarded-For header in the HTTP request before it sends it to targets. |

## Referenced by

- [`ApplicationLoadBalancerProps`](/v2/docs/aws-cdk-lib.aws_elasticloadbalancingv2.ApplicationLoadBalancerProps).xffHeaderProcessingMode