Adjust header names in a request
You can use the serverless Post-Function plugin to detect headers in a request and transform them into custom header names.
In this tutorial, we’ll edit two types of headers: headers set by a plugin (in this case, Rate Limiting), and latency headers from Kong Gateway.
We’ll enable the Post-Function plugin in the header_filter
phase, where it will look for a configured list of headers, then transform those headers into different names.
The upstream service then only sees the transformed header names.
Prerequisites
Kong Konnect
This is a Konnect tutorial and requires a Konnect personal access token.
-
Create a new personal access token by opening the Konnect PAT page and selecting Generate Token.
-
Export your token to an environment variable:
export KONNECT_TOKEN='YOUR_KONNECT_PAT'
-
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 $KONNECT_TOKEN --deck-output
This sets up a Konnect Control Plane named
quickstart
, provisions a local Data Plane, and prints out the following environment variable exports:export DECK_KONNECT_TOKEN=$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'
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.
-
Export your license to an environment variable:
export KONG_LICENSE_DATA='LICENSE-CONTENTS-GO-HERE'
-
Run the quickstart script:
curl -Ls https://get.konghq.com/quickstart | bash -s -- -e KONG_LICENSE_DATA
Once Kong Gateway is ready, you will see the following message:
Kong Gateway Ready
decK
decK is a CLI tool for managing Kong Gateway declaratively with state files. To complete this tutorial you will first need to install decK.
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:
-
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 ' | deck gateway apply -
To learn more about entities, you can read our entities documentation.
Enable the Rate Limiting plugin
Add a Rate Limiting plugin to the example-service
you created in the prerequisites:
echo '
_format_version: "3.0"
plugins:
- name: rate-limiting
service: example-service
config:
second: 5
minute: 30
policy: local
' | deck gateway apply -
Create a header transformation Lua function
The Post-Function plugin lets you execute Lua code. We’ll pass a function that renames the following headers:
-
Rate limiting headers: The Rate Limiting plugin returns headers such as
X-RateLimit-Remaining-{time}
andX-RateLimit-Limit-{time}
, where{time}
is the configured time span for the limit. -
Latency headers: Kong Gateway adds latency headers to responses, such as
X-Kong-Upstream-Latency
andX-Kong-Proxy-Latency
. While you can turn these headers on or off inkong.conf
, they have fixed names that can’t be configured.
Run the following command to create a rename-headers.lua
file:
cat <<EOF > rename-headers.lua
return function()
local kong_rl_headers = {}
kong_rl_headers["x-ratelimit-limit-second"]="X-Rlls"
kong_rl_headers["x-ratelimit-remaining-second"]="X-Rlrs"
kong_rl_headers["x-ratelimit-limit-minute"]="X-Rllm"
kong_rl_headers["x-ratelimit-remaining-minute"]="X-Rlrm"
kong_rl_headers["x-ratelimit-limit-hour"]="X-Rllh"
kong_rl_headers["x-ratelimit-remaining-hour"]="X-Rlrh"
kong_rl_headers["x-ratelimit-limit-day"]="X-Rlld"
kong_rl_headers["x-ratelimit-remaining-day"]="X-Rlrd"
kong_rl_headers["x-ratelimit-limit-month"]="X-Rlln"
kong_rl_headers["x-ratelimit-remaining-month"]="X-Rlrn"
kong_rl_headers["x-ratelimit-limit-year"]="X-Rlly"
kong_rl_headers["x-ratelimit-remaining-year"]="X-Rlry"
local headers = kong.response.get_headers()
for k, v in pairs(headers) do
if kong_rl_headers[k] ~= nil then
kong.response.set_header(kong_rl_headers[k], v)
kong.response.clear_header(k)
end
end
-- Add custom headers for latency
kong.response.set_header("My-Custom-Proxy-Latency", ngx.ctx.KONG_PROXY_LATENCY)
kong.response.set_header("My-Custom-Upstream-Latency", ngx.ctx.KONG_WAITING_TIME)
end
EOF
Add the rename-headers.lua
file as a decK environment variable so that you can pass this file to decK:
export DECK_RENAME_HEADERS="$(cat rename-headers.lua)"
Enable the Post-Function plugin
To change the header names, set up a Post-Function plugin instance that runs globally in the header_filter
phase, and pass the function as an environment variable:
echo '
_format_version: "3.0"
plugins:
- name: post-function
route: example-route
config:
header_filter:
- |
${{ env "DECK_RENAME_HEADERS" | indent 8 }}
' | deck gateway apply -
Validate
Let’s test that the response header names have changed:
curl -i "$KONNECT_PROXY_URL/anything"
curl -i "http://localhost:8000/anything"
The response should show the new header names.
Cleanup
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.
Destroy the Kong Gateway container
curl -Ls https://get.konghq.com/quickstart | bash -s -- -d