+++
title = "Response-Transformer plugin"
weight = 12
+++

#### Introduction
The [Response-Transformer](https://docs.konghq.com/hub/kong-inc/response-transformer/) plugin modifies the upstream response (e.g. response from the server) before returning it to the client.

In this section, you will configure the Response-Transformer plugin on the ingress resource. Specifically, you will configure Kong to modify the echo-server header to include "demo: injected-by-kong" before responding to the client.

#### Create KongPlugin resource
Create a KongPlugin resource, by configuring Kong for Kubernetes to execute the Response-Transformer plugin whenever a request matching the ingress rule is processed.

```bash
echo '
apiVersion: configuration.konghq.com/v1
kind: KongPlugin
metadata:
  name: add-response-header
config:
  add:
    headers:
    - "demo: injected-by-kong"
plugin: response-transformer
' | kubectl apply -f -
```

**Response**
```
kongplugin.configuration.konghq.com/add-response-header created
```

### Associate plugin with the ingress rule

Associate the Response-Transformer plugin with the ingress rule you created previously.

```bash
kubectl patch ingress demo -p '{"metadata":{"annotations":{"konghq.com/plugins":"add-response-header"}}}'
```

### Verify
Test to make sure Kong transforms the request to the echo server and httpbin server. 

**Request 1**
```bash
curl -I $DATA_PLANE_LB/bar
```

**Response**
```
HTTP/1.1 200 OK
Content-Type: text/plain; charset=UTF-8
Connection: keep-alive
Date: Tue, 19 Oct 2021 19:41:18 GMT
Server: echoserver
demo:  injected-by-kong
X-Kong-Upstream-Latency: 0
X-Kong-Proxy-Latency: 0
Via: kong/2.6.0.0-enterprise-edition
```


**Request 2**
```bash
curl -i $DATA_PLANE_LB/foo/status/200
```

**Response**
```
HTTP/1.1 200 OK
Content-Type: text/html; charset=utf-8
Content-Length: 0
Connection: keep-alive
Server: gunicorn/19.9.0
Date: Tue, 19 Oct 2021 19:41:54 GMT
Access-Control-Allow-Origin: *
Access-Control-Allow-Credentials: true
demo:  injected-by-kong
X-Kong-Upstream-Latency: 2
X-Kong-Proxy-Latency: 0
Via: kong/2.6.0.0-enterprise-edition
```

#### Results

Notice in the response "demo:  injected-by-kong" in injected in the header. Kong modifies the response with the Response-Transformer plugin when the requests matches the ingress rule defined in the demo ingress resource.  


#### What happens if you send request to /baz?
Send a request to  /baz.

```bash
curl -I $DATA_PLANE_LB/baz
```

**Response**
```
HTTP/1.1 200 OK
Content-Type: text/html; charset=utf-8
Content-Length: 9593
Connection: keep-alive
Server: gunicorn/19.9.0
Date: Tue, 19 Oct 2021 19:42:26 GMT
Access-Control-Allow-Origin: *
Access-Control-Allow-Credentials: true
X-Kong-Upstream-Latency: 3
X-Kong-Proxy-Latency: 0
Via: kong/2.6.0.0-enterprise-edition
```



#### Results
If you send a request httpbin service with path /baz,  the header is not injected by Kong since this endpoint was not configured for the Response-Transformer plugin



#### Conclusion

You have successfully setup a plugin which is executed only when a request matches a specific Ingress rule.

Specifically, you configured Kong to modify the echo-server header to include "demo: injected-by-kong" before responding to the client. 

#### Cleanup

Delete the Kong plugin by running following command. Cleanup ensures that this plugin does not interferes with any other modules in the workshop for demo purposes and each workshop module code continues to function indepdently.

```bash
kubectl delete kongplugin add-response-header
```

In real world scenario, you can enable as many plugins as you like depending on your use cases.