Exit Transformer: Customize the 404 error message - Plugin

Customize the 404 error message

Configure the plugin to transform 404 responses and add a custom error message. See Transform a 404 response message for a full how-to guide with this example.

Prerequisites

untrusted_lua must be set to either on or sandbox in your kong.conf file for this plugin to work.

Set up the plugin

Add this section to your declarative configuration file:

_format_version: "3.0"
plugins:
  - name: exit-transformer
    config:
      handle_unknown: true
      functions:
      - return function(status, body, headers) if status == 404 then local new_body
        = { error = true, status = status, message = "This is not the Route you are
        looking for", } return status, new_body, headers else return status, body, headers
        end end

Make the following request:

curl -i -X POST http://localhost:8001/plugins/ \
    --header "Accept: application/json" \
    --header "Content-Type: application/json" \
    --data '
    {
      "name": "exit-transformer",
      "config": {
        "handle_unknown": true,
        "functions": [
          "return function(status, body, headers) if status == 404 then local new_body = { error = true, status = status, message = \"This is not the Route you are looking for\", } return status, new_body, headers else return status, body, headers end end"
        ]
      }
    }
    '

Make the following request:

curl -X POST https://{region}.api.konghq.com/v2/control-planes/{controlPlaneId}/core-entities/plugins/ \
    --header "accept: application/json" \
    --header "Content-Type: application/json" \
    --header "Authorization: Bearer $KONNECT_TOKEN" \
    --data '
    {
      "name": "exit-transformer",
      "config": {
        "handle_unknown": true,
        "functions": [
          "return function(status, body, headers) if status == 404 then local new_body = { error = true, status = status, message = \"This is not the Route you are looking for\", } return status, new_body, headers else return status, body, headers end end"
        ]
      }
    }
    '

Make sure to replace the following placeholders with your own values:

region: Geographic region where your Kong Konnect is hosted and operates.
controlPlaneId: The id of the control plane.
KONNECT_TOKEN: Your Personal Access Token (PAT) associated with your Konnect account.

See the Konnect API reference to learn about region-specific URLs and personal access tokens.

echo "
apiVersion: configuration.konghq.com/v1
kind: KongClusterPlugin
metadata:
  name: exit-transformer
  namespace: kong
  annotations:
    kubernetes.io/ingress.class: kong
  labels:
    global: 'true'
config:
  handle_unknown: true
  functions:
  - return function(status, body, headers) if status == 404 then local new_body =
    { error = true, status = status, message = 'This is not the Route you are looking
    for', } return status, new_body, headers else return status, body, headers end
    end
plugin: exit-transformer
" | kubectl apply -f -

Prerequisite: Configure your Personal Access Token

terraform {
  required_providers {
    konnect = {
      source  = "kong/konnect"
    }
  }
}

provider "konnect" {
  personal_access_token = "$KONNECT_TOKEN"
  server_url            = "https://us.api.konghq.com/"
}

Add the following to your Terraform configuration to create a Konnect Gateway Plugin:

resource "konnect_gateway_plugin_exit_transformer" "my_exit_transformer" {
  enabled = true

  config = {
    handle_unknown = true
    functions = ["return function(status, body, headers) if status == 404 then local new_body = { error = true, status = status, message = \"This is not the Route you are looking for\", } return status, new_body, headers else return status, body, headers end end"]
  }

  control_plane_id = konnect_gateway_control_plane.my_konnect_cp.id
}

Exit Transformer

Customize the 404 error message

Prerequisites

Set up the plugin

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