Response Transformer plugin

Transform the response sent by the upstream server on the fly before returning the response to the client.

Note on transforming bodies: Be aware of the performance of transformations on the response body. In order to parse and modify a JSON body, the plugin needs to retain it in memory, which might cause pressure on the worker's Lua VM when dealing with large bodies (several MBs). Because of Nginx's internals, the `Content-Length` header will not be set when transforming a response body.

For additional response transformation features, check out the Response Transformer Advanced plugin. Response Transformer Advanced adds the following abilities:

When transforming a JSON payload, transformations are applied to nested JSON objects and arrays. This can be turned off and on using the config.dots_in_keys configuration parameter. See Response Transformed Advanced arrays and nested objects.
Transformations can be restricted to responses with specific status codes using various config.*.if_status configuration parameters.
JSON body contents can be restricted to a set of allowed properties with config.allow.json.
The entire response body can be replaced using config.replace.body.
Arbitrary transformation functions written in Lua can be applied.
The plugin will decompress and recompress Gzip-compressed payloads when the Content-Encoding header is gzip.

Response Transformer Advanced includes the following additional configurations: add.if_status, append.if_status, remove.if_status, replace.body, replace.if_status, transform.functions, transform.if_status, allow.json, rename.if_status, transform.json, and dots_in_keys.

Configuration Reference

This plugin is compatible with DB-less mode.

In DB-less mode, you configure Kong Gateway declaratively. Therefore, the Admin API is mostly read-only. The only tasks it can perform are all related to handling the declarative config, including:

Setting a target's health status in the load balancer
Validating configurations against schemas
Uploading the declarative configuration using the /config endpoint

Example plugin configuration

Enable on a service

Enable on a route

Enable on a consumer

Enable globally

The following examples provide some typical configurations for enabling the response-transformer plugin on a service.

Admin API

Kubernetes

Declarative (YAML)

Konnect Cloud

Kong Manager

Make the following request:

curl -X POST http://localhost:8001/services/SERVICE_NAME|SERVICE_ID/plugins \
    --data "name=response-transformer"  \
    --data "config.remove.headers=x-toremove" \
    --data "config.remove.headers=x-another-one" \
    --data "config.remove.json=json-key-toremove" \
    --data "config.remove.json=another-json-key" \
    --data "config.add.headers=x-new-header:value" \
    --data "config.add.headers=x-another-header:something" \
    --data "config.add.json=new-json-key:some_value" \
    --data "config.add.json=another-json-key:some_value" \
    --data "config.add.json_types=new-json-key:string" \
    --data "config.add.json_types=another-json-key:boolean" \
    --data "config.add.json_types=another-json-key:number" \
    --data "config.append.headers=x-existing-header:some_value" \
    --data "config.append.headers=x-another-header:some_value"

Replace SERVICE_NAME|SERVICE_ID with the id or name of the service that this plugin configuration will target.

First, create a KongPlugin resource:

apiVersion: configuration.konghq.com/v1
kind: KongPlugin
metadata:
  name: response-transformer-example
config: 
  remove:
    headers:
    - x-toremove
    - x-another-one
  remove:
    json:
    - json-key-toremove
    - another-json-key
  add:
    headers:
    - x-new-header:value
    - x-another-header:something
  add:
    json:
    - new-json-key:some_value
    - another-json-key:some_value
  add:
    json_types:
    - new-json-key:string
    - another-json-key:boolean
    - another-json-key:number
  append:
    headers:
    - x-existing-header:some_value
    - x-another-header:some_value
plugin: response-transformer

Next, apply the KongPlugin resource to a service by annotating the service as follows:

apiVersion: v1
kind: Service
metadata:
  name: SERVICE_NAME|SERVICE_ID
  labels:
    app: SERVICE_NAME|SERVICE_ID
  annotations:
    konghq.com/plugins: response-transformer-example
spec:
  ports:
  - port: 80
    targetPort: 80
    protocol: TCP
    name: SERVICE_NAME|SERVICE_ID
  selector:
    app: SERVICE_NAME|SERVICE_ID

Replace SERVICE_NAME|SERVICE_ID with the id or name of the service that this plugin configuration will target.

Note: The KongPlugin resource only needs to be defined once and can be applied to any service, consumer, or route in the namespace. If you want the plugin to be available cluster-wide, create the resource as a KongClusterPlugin instead of KongPlugin.

Add this section to your declarative configuration file:

plugins:
- name: response-transformer
  service: SERVICE_NAME|SERVICE_ID
  config: 
    remove:
      headers:
      - x-toremove
      - x-another-one
    remove:
      json:
      - json-key-toremove
      - another-json-key
    add:
      headers:
      - x-new-header:value
      - x-another-header:something
    add:
      json:
      - new-json-key:some_value
      - another-json-key:some_value
    add:
      json_types:
      - new-json-key:string
      - another-json-key:boolean
      - another-json-key:number
    append:
      headers:
      - x-existing-header:some_value
      - x-another-header:some_value

Replace SERVICE_NAME|SERVICE_ID with the id or name of the service that this plugin configuration will target.

You can configure this plugin through the Konnect UI.

From the Service Hub, select a service version, then set up the plugin:

In the Plugins section, click Add Plugin.
Find and select the Response Transformer plugin.
Click Create.

You can configure this plugin through the Kong Manager UI.

In Kong Manager, select the workspace.
From the Services section, click View for the service row.
From the plugin section, click Add Plugin.
Find and select the Response Transformer plugin.
If the option is available, select Scoped.
Add the service name and ID to the Service field if it is not already pre-filled.
Click Create.

The following examples provide some typical configurations for enabling the response-transformer plugin on a route.

Admin API

Kubernetes

Declarative (YAML)

Konnect Cloud

Kong Manager

Make the following request:

curl -X POST http://localhost:8001/routes/ROUTE_NAME|ROUTE_ID/plugins \
  --data "name=response-transformer"  \
    --data "config.remove.headers=x-toremove" \
    --data "config.remove.headers=x-another-one" \
    --data "config.remove.json=json-key-toremove" \
    --data "config.remove.json=another-json-key" \
    --data "config.add.headers=x-new-header:value" \
    --data "config.add.headers=x-another-header:something" \
    --data "config.add.json=new-json-key:some_value" \
    --data "config.add.json=another-json-key:some_value" \
    --data "config.add.json_types=new-json-key:string" \
    --data "config.add.json_types=another-json-key:boolean" \
    --data "config.add.json_types=another-json-key:number" \
    --data "config.append.headers=x-existing-header:some_value" \
    --data "config.append.headers=x-another-header:some_value"

Replace ROUTE_NAME|ROUTE_ID with the id or name of the route that this plugin configuration will target.

First, create a KongPlugin resource:

apiVersion: configuration.konghq.com/v1
kind: KongPlugin
metadata:
  name: response-transformer-example
config: 
  remove:
    headers:
    - x-toremove
    - x-another-one
  remove:
    json:
    - json-key-toremove
    - another-json-key
  add:
    headers:
    - x-new-header:value
    - x-another-header:something
  add:
    json:
    - new-json-key:some_value
    - another-json-key:some_value
  add:
    json_types:
    - new-json-key:string
    - another-json-key:boolean
    - another-json-key:number
  append:
    headers:
    - x-existing-header:some_value
    - x-another-header:some_value
plugin: response-transformer

Then, apply it to an ingress (route or routes) by annotating the ingress as follows:

apiVersion: networking.k8s.io/v1
kind: Ingress
metadata:
  name: ROUTE_NAME|ROUTE_ID
  annotations:
    kubernetes.io/ingress.class: kong
    konghq.com/plugins: response-transformer-example
spec:
  rules:
  - host: examplehostname.com
    http:
      paths:
      - path: /bar
        backend:
          service:
            name: echo
            port:
              number: 80

Replace ROUTE_NAME|ROUTE_ID with the id or name of the route that this plugin configuration will target.

Note: The KongPlugin resource only needs to be defined once and can be applied to any service, consumer, or route in the namespace. If you want the plugin to be available cluster-wide, create the resource as a KongClusterPlugin instead of KongPlugin.

Add this section to your declarative configuration file:

plugins:
- name: response-transformer
  route: ROUTE_NAME
  config: 
    remove:
      headers:
      - x-toremove
      - x-another-one
    remove:
      json:
      - json-key-toremove
      - another-json-key
    add:
      headers:
      - x-new-header:value
      - x-another-header:something
    add:
      json:
      - new-json-key:some_value
      - another-json-key:some_value
    add:
      json_types:
      - new-json-key:string
      - another-json-key:boolean
      - another-json-key:number
    append:
      headers:
      - x-existing-header:some_value
      - x-another-header:some_value

Replace ROUTE_NAME|ROUTE_ID with the id or name of the route that this plugin configuration will target.

You can configure this plugin through the Konnect UI.

From the Service Hub, select a service version, then set up the plugin:

Select a route.
In the Plugins section, click Add Plugin.
Find and select the Response Transformer plugin.
Click Create.

You can configure this plugin through the Kong Manager UI.

In Kong Manager, select the workspace.
Open Routes from the menu, then click View for the route row.
From the plugin section, click Add Plugin.
Find and select the Response Transformer plugin.
If the option is available, select Scoped.
Add the route ID if it is not already prefilled.
Click Create.

The following examples provide some typical configurations for enabling the response-transformer plugin on a consumer.

Admin API

Kubernetes

Declarative (YAML)

Kong Manager

Make the following request:

curl -X POST http://localhost:8001/consumers/CONSUMER_NAME|CONSUMER_ID/plugins \
  --data "name=response-transformer"  \
    --data "config.remove.headers=x-toremove" \
    --data "config.remove.headers=x-another-one" \
    --data "config.remove.json=json-key-toremove" \
    --data "config.remove.json=another-json-key" \
    --data "config.add.headers=x-new-header:value" \
    --data "config.add.headers=x-another-header:something" \
    --data "config.add.json=new-json-key:some_value" \
    --data "config.add.json=another-json-key:some_value" \
    --data "config.add.json_types=new-json-key:string" \
    --data "config.add.json_types=another-json-key:boolean" \
    --data "config.add.json_types=another-json-key:number" \
    --data "config.append.headers=x-existing-header:some_value" \
    --data "config.append.headers=x-another-header:some_value"

Replace CONSUMER_NAME|CONSUMER_ID with the id or name of the consumer that this plugin configuration will target.

You can combine consumer.id, service.id, or route.id in the same request, to further narrow the scope of the plugin.

First, create a KongPlugin resource:

apiVersion: configuration.konghq.com/v1
kind: KongPlugin
metadata:
  name: response-transformer-example
config: 
  remove:
    headers:
    - x-toremove
    - x-another-one
  remove:
    json:
    - json-key-toremove
    - another-json-key
  add:
    headers:
    - x-new-header:value
    - x-another-header:something
  add:
    json:
    - new-json-key:some_value
    - another-json-key:some_value
  add:
    json_types:
    - new-json-key:string
    - another-json-key:boolean
    - another-json-key:number
  append:
    headers:
    - x-existing-header:some_value
    - x-another-header:some_value
plugin: response-transformer

Then, apply it to a consumer by annotating the KongConsumer resource as follows:

apiVersion: configuration.konghq.com/v1
kind: KongConsumer
metadata:
  name: CONSUMER_NAME|CONSUMER_ID
  annotations:
    konghq.com/plugins: response-transformer-example
    kubernetes.io/ingress.class: kong

Replace CONSUMER_NAME|CONSUMER_ID with the id or name of the consumer that this plugin configuration will target.

Note: The KongPlugin resource only needs to be defined once and can be applied to any service, consumer, or route in the namespace. If you want the plugin to be available cluster-wide, create the resource as a KongClusterPlugin instead of KongPlugin.

Add this section to your declarative configuration file:

plugins:
- name: response-transformer
  consumer: CONSUMER_NAME|CONSUMER_ID
  config: 
    remove:
      headers:
      - x-toremove
      - x-another-one
    remove:
      json:
      - json-key-toremove
      - another-json-key
    add:
      headers:
      - x-new-header:value
      - x-another-header:something
    add:
      json:
      - new-json-key:some_value
      - another-json-key:some_value
    add:
      json_types:
      - new-json-key:string
      - another-json-key:boolean
      - another-json-key:number
    append:
      headers:
      - x-existing-header:some_value
      - x-another-header:some_value

Replace CONSUMER_NAME|CONSUMER_ID with the id or name of the consumer that this plugin configuration will target.

You can configure this plugin through the Kong Manager UI.

In Kong Manager, select the workspace.
From the Consumers section, click View for the consumer row.
Select the Plugins tab, then click Add Plugin.
Find and select the Response Transformer plugin.
If the option is available, select Scoped.
Add the consumer ID if it is not already prefilled.
Click Create.

A plugin which is not associated to any service, route, or consumer is considered global, and will be run on every request. Read the Plugin Reference and the Plugin Precedence sections for more information.

The following examples provide some typical configurations for enabling the response-transformer plugin globally.

Admin API

Kubernetes

Declarative (YAML)

Kong Manager

Make the following request:

curl -X POST http://localhost:8001/plugins/ \
  --data "name=response-transformer"  \
    --data "config.remove.headers=x-toremove" \
    --data "config.remove.headers=x-another-one" \
    --data "config.remove.json=json-key-toremove" \
    --data "config.remove.json=another-json-key" \
    --data "config.add.headers=x-new-header:value" \
    --data "config.add.headers=x-another-header:something" \
    --data "config.add.json=new-json-key:some_value" \
    --data "config.add.json=another-json-key:some_value" \
    --data "config.add.json_types=new-json-key:string" \
    --data "config.add.json_types=another-json-key:boolean" \
    --data "config.add.json_types=another-json-key:number" \
    --data "config.append.headers=x-existing-header:some_value" \
    --data "config.append.headers=x-another-header:some_value"

Create a KongClusterPlugin resource and label it as global:

apiVersion: configuration.konghq.com/v1
kind: KongClusterPlugin
metadata:
  name: <global-response-transformer>
  annotations:
    kubernetes.io/ingress.class: kong
  labels:
    global: \"true\"
config: 
  remove:
    headers:
    - x-toremove
    - x-another-one
  remove:
    json:
    - json-key-toremove
    - another-json-key
  add:
    headers:
    - x-new-header:value
    - x-another-header:something
  add:
    json:
    - new-json-key:some_value
    - another-json-key:some_value
  add:
    json_types:
    - new-json-key:string
    - another-json-key:boolean
    - another-json-key:number
  append:
    headers:
    - x-existing-header:some_value
    - x-another-header:some_value
plugin: response-transformer

Add a plugins entry in the declarative configuration file:

plugins:
- name: response-transformer
  config: 
    remove:
      headers:
      - x-toremove
      - x-another-one
    remove:
      json:
      - json-key-toremove
      - another-json-key
    add:
      headers:
      - x-new-header:value
      - x-another-header:something
    add:
      json:
      - new-json-key:some_value
      - another-json-key:some_value
    add:
      json_types:
      - new-json-key:string
      - another-json-key:boolean
      - another-json-key:number
    append:
      headers:
      - x-existing-header:some_value
      - x-another-header:some_value

You can configure this plugin through the Kong Manager UI.

In Kong Manager, select the workspace.
Open Plugins from the menu, then click New Plugin.
Find and select the Response Transformer plugin.
If the option is available, set the plugin scope to Global.
Click Create.

Parameters

Here's a list of all the parameters which can be used in this plugin's configuration:

Form Parameter	Description
`name` required Type: string	The name of the plugin, in this case `response-transformer`.
`service.name` or `service.id` Type: string	The name or ID of the service the plugin targets. Set one of these parameters if adding the plugin to a service through the top-level `/plugins` endpoint. Not required if using `/services/SERVICE_NAME\|SERVICE_ID/plugins`.
`route.name` or `route.id` Type: string	The name or ID of the route the plugin targets. Set one of these parameters if adding the plugin to a route through the top-level `/plugins` endpoint. Not required if using `/routes/ROUTE_NAME\|ROUTE_ID/plugins`.
`consumer.name` or `consumer.id` Type: string	The name or ID of the consumer the plugin targets. Set one of these parameters if adding the plugin to a consumer through the top-level `/plugins` endpoint. Not required if using `/consumers/CONSUMER_NAME\|CONSUMER_ID/plugins`.
`enabled` Type: boolean Default value: `true`	Whether this plugin will be applied.
`config.remove.headers` optional Type: array of string elements	List of header names. Unset the header(s) with the given name.
`config.remove.json` optional Type: array of string elements	List of property names. Remove the property from the JSON body if it is present.
`config.rename.headers` optional Type: array of string elements	List of `original_header_name:new_header_name` pairs. If the header `original_headername` is already set, rename it to `new_headername`. Ignored if the header is not already set.
`config.replace.headers` optional Type: array of string elements	List of `headername:value` pairs. If and only if the header is already set, replace its old value with the new one. Ignored if the header is not already set.
`config.replace.json` optional Type: array of string elements	List of `property:value` pairs. If and only if the parameter is already present, replace its old value with the new one. Ignored if the parameter is not already present.
`config.replace.json_types` optional Type: array of string elements	List of JSON type names. Specify the types of the JSON values returned when replacing JSON properties. Each string element can be one of: boolean, number, or string.
`config.add.headers` optional Type: array of string elements	List of `headername:value` pairs. If and only if the header is not already set, set a new header with the given value. Ignored if the header is already set.
`config.add.json` optional Type: array of string elements	List of `property:value` pairs. If and only if the property is not present, add a new property with the given value to the JSON body. Ignored if the property is already present.
`config.add.json_types` optional Type: array of string elements	List of JSON type names. Specify the types of the JSON values returned when adding a new JSON property. Each string element can be one of: boolean, number, or string.
`config.append.headers` optional Type: array of string elements	List of `headername:value` pairs. If the header is not set, set it with the given value. If it is already set, a new header with the same name and the new value will be set. Each string element can be one of: boolean, number, or string.
`config.append.json` optional Type: array of string elements	List of `property:value` pairs. If the property is not present in the JSON body, add it with the given value. If it is already present, the two values (old and new) will be aggregated in an array.
`config.append.json_types` optional Type: array of string elements	List of JSON type names. Specify the types of the JSON values returned when appending JSON properties. Each string element can be one of: boolean, number, or string.

Note: if the value contains a , then the comma separated format for lists cannot be used. The array notation must be used instead.

Order of execution

Plugin performs the response transformation in following order

remove –> rename –> replace –> add –> append

Examples

In these examples we have the plugin enabled on a Route. This would work similar for Services.

Add multiple headers by passing each header:value pair separately:

With a database

Without a database

curl -X POST http://localhost:8001/routes/{route}/plugins \
  --data "name=response-transformer" \
  --data "config.add.headers[1]=h1:v1" \
  --data "config.add.headers[2]=h2:v1"

plugins:
- name: response-transformer
  route: {route}
  config:
    add:
      headers: ["h1:v1", "h2:v2"]

upstream response headers	proxied response headers
h1: v1	h1: v1 h2: v1

Add multiple headers by passing comma separated header:value pair (only possible with a database):

curl -X POST http://localhost:8001/routes/{route}/plugins \
  --data "name=response-transformer" \
  --data "config.add.headers=h1:v1,h2:v2"

upstream response headers	proxied response headers
h1: v1	h1: v1 h2: v1

Add multiple headers passing config as JSON body (only possible with a database):

curl -X POST http://localhost:8001/routes/{route}/plugins \
  --header 'content-type: application/json' \
  --data '{"name": "response-transformer", "config": {"add": {"headers": ["h1:v2", "h2:v1"]}}}'

upstream response headers	proxied response headers
h1: v1	h1: v1 h2: v1

Add a body property and a header:

With a database

Without a database

curl -X POST http://localhost:8001/routes/{route}/plugins \
  --data "name=response-transformer" \
  --data "config.add.json=p1:v1,p2=v2" \
  --data "config.add.headers=h1:v1"

plugins:
- name: response-transformer
  route: {route}
  config:
    add:
      json: ["p1:v1", "p2=v2"]
      headers: ["h1:v1"]

upstream response headers	proxied response headers
h1: v2	h1: v2 h2: v1
h3: v1	h1: v1 h2: v1 h3: v1

upstream response JSON body	proxied response body
{}	{“p1” : “v1”, “p2”: “v2”}
{“p1” : “v2”}	{“p1” : “v2”, “p2”: “v2”}

Append multiple headers and remove a body property:

With a database

Without a database

curl -X POST http://localhost:8001/routes/{route}/plugins \
  --header 'content-type: application/json' \
  --data '{"name": "response-transformer", "config": {"append": {"headers": ["h1:v2", "h2:v1"]}, "remove": {"json": ["p1"]}}}'

plugins:
- name: response-transformer
  route: {route}
  config:
    append:
      headers: ["h1:v2", "h2:v1"]
    remove:
      json: ["p1"]

upstream response headers	proxied response headers
h1: v1	h1: v1 h1: v2 h2: v1

upstream response JSON body	proxied response body
{“p2”: “v2”}	{“p2”: “v2”}
{“p1” : “v1”, “p2” : “v1”}	{“p2”: “v2”}

Explicitly set the type of the added JSON value -1 to be a number (instead of the implicitly inferred type string) if the response code is 500:

curl -X POST http://localhost:8001/routes/{route}/plugins \
  --data "name=response-transformer" \
  --data "config.add.json=p1:-1" \
  --data "config.add.json_types=number"

About this Plugin
Plugin Version	3.0.x
Made by	Kong Inc.
Categories	Transformations
DB-less compatible?	Yes
Konnect Cloud compatible?	Yes
Compatible protocols	`http` `https`