curl -X GET "$KONNECT_PROXY_URL/anything" \
--no-progress-meter --fail-with-body \
-H "x-block: true"
Copied!
Configure conditional plugin execution in Kong Gateway
Deployment Platform
Related Documentation
Related Resources
Minimum Version
Kong Gateway - 3.14
TL;DR
The condition field on a plugin lets you write an ATC expression that controls whether the plugin runs for a given request.
Attach a condition to the Request Termination plugin so that it only triggers when a specific request header is present.
While this guide uses a particular plugin, you can use conditions like this with any plugin that contains a condition field.
Prerequisites
Kong Konnect
This is a Konnect tutorial and requires a Konnect personal access token.
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Create a new personal access token by opening the Konnect PAT page and selecting Generate Token.
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Export your token to an environment variable:
export KONNECT_TOKEN='YOUR_KONNECT_PAT'Copied! -
Run the quickstart script to automatically provision a Control Plane and Data Plane, and configure your environment:
curl -Ls https://get.konghq.com/quickstart | bash -s -- -k $KONNECT_TOKEN --deck-outputCopied!This sets up a Konnect Control Plane named
quickstart, provisions a local Data Plane, and prints out the following environment variable exports:export DECK_KONNECT_TOKEN=$KONNECT_TOKEN export DECK_KONNECT_CONTROL_PLANE_NAME=quickstart export KONNECT_CONTROL_PLANE_URL=https://us.api.konghq.com export KONNECT_PROXY_URL='http://localhost:8000'Copied!Copy and paste these into your terminal to configure your session.
Kong Gateway running
This tutorial requires Kong Gateway Enterprise. If you don’t have Kong Gateway set up yet, you can use the quickstart script with an enterprise license to get an instance of Kong Gateway running almost instantly.
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Export your license to an environment variable:
export KONG_LICENSE_DATA='LICENSE-CONTENTS-GO-HERE'Copied! -
Run the quickstart script:
curl -Ls https://get.konghq.com/quickstart | bash -s -- -e KONG_LICENSE_DATACopied!Once Kong Gateway is ready, you will see the following message:
Kong Gateway Ready
decK v1.43+
decK is a CLI tool for managing Kong Gateway declaratively with state files. To complete this tutorial, install decK version 1.43 or later.
This guide uses deck gateway apply, which directly applies entity configuration to your Gateway instance.
We recommend upgrading your decK installation to take advantage of this tool.
You can check your current decK version with deck version.
Required entities
For this tutorial, you’ll need Kong Gateway entities, like Gateway Services and Routes, pre-configured. These entities are essential for Kong Gateway to function but installing them isn’t the focus of this guide. Follow these steps to pre-configure them:
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Run the following command:
echo ' _format_version: "3.0" services: - name: example-service url: http://httpbin.konghq.com/anything routes: - name: example-route paths: - "/anything" service: name: example-service protocols: - http - https ' | deck gateway apply -Copied!
To learn more about entities, you can read our entities documentation.
Add a plugin with a condition
Add the Request Termination plugin to your Route with a condition expression.
In this example, the plugin only triggers when the request includes the header x-block: true, and blocks the request.
Requests without this header are proxied to the upstream service.
curl -X POST "$KONNECT_CONTROL_PLANE_URL/routes/example-route/plugins" \
--no-progress-meter --fail-with-body \
-H "Accept: application/json"\
-H "Content-Type: application/json" \
--json '{
"name": "request-termination",
"config": {
"status_code": 403,
"message": "Forbidden by condition"
},
"condition": "http.headers.x_block == \"true\""
}'
Copied!
curl -X POST "http://localhost:8001/routes/example-route/plugins" \
--no-progress-meter --fail-with-body \
-H "Accept: application/json"\
-H "Content-Type: application/json" \
--json '{
"name": "request-termination",
"config": {
"status_code": 403,
"message": "Forbidden by condition"
},
"condition": "http.headers.x_block == \"true\""
}'
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Note: In ATC expressions, hyphens (
-) in header names must be replaced with underscores (_). For example,x-blockbecomeshttp.headers.x_block.
Validate
Let’s check that the plugin gets accurately applied based on the condition.
First, send a request with the x-block: true header:
curl -X GET "http://localhost:8000/anything" \
--no-progress-meter --fail-with-body \
-H "x-block: true"
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The header satisfies the condition and triggers the Request Termination plugin, so you should receive a 403 Forbidden response:
{"message":"Forbidden by condition"}
Next, send a request without the header:
curl -X GET "$KONNECT_PROXY_URL/anything" \
--no-progress-meter --fail-with-body
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curl -X GET "http://localhost:8000/anything" \
--no-progress-meter --fail-with-body
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You should receive a 200 OK response from the upstream service, because the condition evaluated to false and the plugin was skipped.
Cleanup
Destroy the Kong Gateway container
curl -Ls https://get.konghq.com/quickstart | bash -s -- -d
Copied!
Clean up Konnect environment
If you created a new control plane and want to conserve your free trial credits or avoid unnecessary charges, delete the new control plane used in this tutorial.
FAQs
Can I see the results of a condition check in the Kong Gateway logs?
If Kong Gateway is running with debug logging enabled, you can confirm the condition evaluation
result in error.log:
[kong] plugin_condition.lua:234 plugin condition evaluated for plugin
'request-termination' (ID: 66a1adbb-0179-49af-a065-4d0bc6c28cd6), result=false
The log line shows the plugin name, its ID, and the result.
When result=false, the plugin was skipped for that request.