Kubernetes rewrite-target paths for appending path to match - kubernetes

Question

I'm using the OSS ingress-nginx Ingress controller and trying to create a rewrite-target rule such that I can append a path string before my string match.
If I wanted to create a rewrite rule with regex that matches /matched/path and rewrites that to /prefix/matched/path, how might I be able to do that?
I've tried something like the following but it's no good, and I'm just confused about the syntax of this ingress definition:
metadata:
annotations:
kubernetes.io/ingress.class: nginx
nginx.ingress.kubernetes.io/rewrite-target: /$2
spec:
rules:
- path: /(/prefix/)(/|$)(/matched/path)(.*)
backend:
serviceName: webapp1

Answer 1

If I wanted to create a rewrite rule with regex that matches
/matched/path and rewrites that to /prefix/matched/path, how might
I be able to do that?
In order to achieve this you have add /prefix into your rewrite-target.
Here's a working example with ingress syntax from k8s v1.18:
apiVersion: networking.k8s.io/v1beta1
kind: Ingress
metadata:
name: example-ingress-v118
annotations:
nginx.ingress.kubernetes.io/rewrite-target: /prefix/$1
spec:
rules:
http:
paths:
- path: /(matched/path/?.*)
backend:
serviceName: test
servicePort: 80
Since the syntax for the new ingress changed in 1.19 (see release notes and some small info at the end) I`m placing also an example with it:
apiVersion: networking.k8s.io/v1
kind: Ingress
metadata:
name: example-ingress-v119
annotations:
nginx.ingress.kubernetes.io/rewrite-target: /prefix/$1
spec:
rules:
- http:
paths:
- path: /(matched/path/?.*)
pathType: Prefix
backend:
service:
name: test
port:
number: 80
Here is a test with http echo server:
➜ ~ curl 172.17.0.4/matched/path
{
"path": "/prefix/matched/path",
"headers": {
"host": "172.17.0.4",
"x-request-id": "011585443ebc6adcf913db1c506abbe6",
"x-real-ip": "172.17.0.1",
"x-forwarded-for": "172.17.0.1",
"x-forwarded-host": "172.17.0.4",
"x-forwarded-port": "80",
"x-forwarded-proto": "http",
"x-scheme": "http",
"user-agent": "curl/7.52.1",
"accept": "*/*"
},
This rule will also ignore the / at the end of the request:
➜ ~ curl 172.17.0.4/matched/path/
{
"path": "/prefix/matched/path/",
"headers": {
"host": "172.17.0.4",
"x-request-id": "0575e9022d814ba07457395f78dbe0fb",
"x-real-ip": "172.17.0.1",
"x-forwarded-for": "172.17.0.1",
"x-forwarded-host": "172.17.0.4",
"x-forwarded-port": "80",
"x-forwarded-proto": "http",
"x-scheme": "http",
"user-agent": "curl/7.52.1",
"accept": "*/*"
},
Worth to mention some notable differences/changes in the new ingress syntax:
spec.backend -> spec.defaultBackend
serviceName -> service.name
servicePort -> service.port.name (for string values)
servicePort -> service.port.number (for numeric values) pathType no longer has a default value in v1; "Exact", "Prefix", or
"ImplementationSpecific" must be specified Other Ingress API updates
backends can now be resource or service backends
path is no longer required to be a valid regular expression (#89778,
#cmluciano) [SIG API Machinery, Apps, CLI, Network and Testing]