How to reference query parameters inside a Kong's plugin configuration? - query-string

Question

I want to implement a simple redirect using Kong's request-termination & response-transformer plugins. The plugins mostly works, but I have an issue with handling query parameters.
My configuration for the plugins is similar to this (note: I'm using Kong in DB-less mode):
services:
- name: my-redirects
url: http://localhost:8080/
routes:
- name: redirect-route
paths:
- /context$
- /$
plugins:
- name: request-termination
config:
status_code: 301
message: Redirect to main page...
- name: response-transformer
config:
add:
headers:
- Location:/context/
I want to obtain the following behaviour:
User visits http://localhost:8000/ -> redirected to /context/
User visits http://localhost:8000/context -> redirected to /context/
User visits http://localhost:8000/?param=value -> redirected to /context/?param=value
User visits http://localhost:8000/context?param=value -> redirected to /context/?param=value
Basically both / and /context requests should be redirected to /context/ (with a final slash) but query parameters should be preserved.
How can I modify the configuration:
add:
headers:
- Location:/context/
to include query parameters matched in the request? I expect to be able to do something like:
add:
headers:
- Location:/context/$query_params

Answer 1

What we are using to solve this on kong running in kubernetes is to use an ingress Exact rule coupled with a pre-function plugin. It should be easy to adapt it to the non-k8s yaml config:
apiVersion: networking.k8s.io/v1
kind: Ingress
metadata:
name: foo-ingress-redirect
konghq.com/plugins: foo-redirect
spec:
...
rules:
- host: myhost.example
http:
paths:
- path: /foo/bar # redirect /foo/bar to /foo/bar/ via plugin above
pathType: Exact
backend:
...
and then plugin:
apiVersion: configuration.konghq.com/v1
kind: KongPlugin
metadata:
name: foo-redirect
plugin: pre-function
config:
access:
- kong.response.exit(301, '', {['Location'] = '/foo/bar/'})
You can also play with kong.request interface if you need to e.g. pass the original query params on the redirect.
It's a bit convoluted but also did not find a simpler way.