HTTP Redirect

This document discusses FSM Gateway’s request redirection, covering host name, prefix path, and full path redirects, with examples of each method.

Request redirection is a common network application function that allows the server to tell the client: “The resource you requested has been moved to another location, please go to the new location to obtain it.”

The HTTPRoute resource utilizes HTTPRequestRedirectFilter to redirect client to the specified new location.

Prerequisites

  • Kubernetes cluster version v1.21.0 or higher.
  • kubectl CLI
  • FSM Gateway installed via guide doc.

Demonstration

We will follow the sample in HTTP Routing.

In our backend server, there are two paths /headers and /get. The previous one responds all request headers as body, and the latter one responds more information of client than /headers.

To facilitate testing, it’s better to add records to local hosts.

echo $GATEWAY_IP foo.example.com bar.example.com >> /etc/hosts
-bash: /etc/hosts: Permission denied
curl foo.example.com/headers
{
  "headers": {
    "Accept": "*/*",
    "Connection": "keep-alive",
    "Host": "foo.example.com",
    "User-Agent": "curl/7.68.0"
  }
}
curl bar.example.com/get
{
  "args": {},
  "headers": {
    "Accept": "*/*",
    "Connection": "keep-alive",
    "Host": "bar.example.com",
    "User-Agent": "curl/7.68.0"
  },
  "origin": "10.42.0.87",
  "url": "http://bar.example.com/get"
}

Host Name Redirect

The HTTP status code 3XX are used to redirect client to another address. We can redirect all requests to foo.example.com to bar.example.com by responding 301 status and new hostname.

apiVersion: gateway.networking.k8s.io/v1
kind: HTTPRoute
metadata:
  name: http-route-foo
spec:
  parentRefs:
  - name: simple-fsm-gateway
    port: 8000
  hostnames:
  - foo.example.com
  rules:
  - matches:
    - path:
        type: PathPrefix
        value: /
    filters:
    - type: RequestRedirect
      requestRedirect:
        hostname: bar.example.com
        port: 8000
        statusCode: 301
    backendRefs:
    - name: httpbin
      port: 8080

Now, it will return the 301 code and bar.example.com:8000 when requesting foo.example.com.

curl -i http://foo.example.com:8000/get
HTTP/1.1 301 Moved Permanently
Location: http://bar.example.com:8000/get
content-length: 0
connection: keep-alive

By default, curl does not follow location redirecting unless enable it by assign opiton -L.

curl -L http://foo.example.com:8000/get
{
  "args": {},
  "headers": {
    "Accept": "*/*",
    "Connection": "keep-alive",
    "Host": "bar.example.com:8000",
    "User-Agent": "curl/7.68.0"
  },
  "origin": "10.42.0.161",
  "url": "http://bar.example.com:8000/get"
}

Prefix Path Redirect

With path redirection, we can implement what we did with URL Rewriting: redirect the request to /status/{n} to /stream/{n}.

apiVersion: gateway.networking.k8s.io/v1
kind: HTTPRoute
metadata:
  name: http-route-foo
spec:
  parentRefs:
  - name: simple-fsm-gateway
    port: 8000
  hostnames:
  - foo.example.com
  rules:
  - matches:
    - path:
        type: PathPrefix
        value: /status
    filters:
    - type: RequestRedirect
      requestRedirect:
        path:
          type: ReplacePrefixMatch
          replacePrefixMatch: /stream
        statusCode: 301
    backendRefs:
    - name: httpbin
      port: 8080
  - matches:
    backendRefs:
    - name: httpbin
      port: 8080

After update rull, we will get.

curl -i http://foo.example.com:8000/status/204
HTTP/1.1 301 Moved Permanently
Location: http://foo.example.com:8000/stream/204
content-length: 0
connection: keep-alive

Full Path Redirect

We can also change full path during redirecting, such as redirect all /status/xxx to /status/200.

apiVersion: gateway.networking.k8s.io/v1
kind: HTTPRoute
metadata:
  name: http-route-foo
spec:
  parentRefs:
  - name: simple-fsm-gateway
    port: 8000
  hostnames:
  - foo.example.com
  rules:
  - matches:
    - path:
        type: PathPrefix
        value: /status
    filters:
    - type: RequestRedirect
      requestRedirect:
        path:
          type: ReplaceFullPath
          replaceFullPath: /status/200
        statusCode: 301
    backendRefs:
    - name: httpbin
      port: 8080
  - matches:
    backendRefs:
    - name: httpbin
      port: 8080      

Now, the status of requests to /status/xxx will be redirected to /status/200.

curl -i http://foo.example.com:8000/status/204
HTTP/1.1 301 Moved Permanently
Location: http://foo.example.com:8000/status/200
content-length: 0
connection: keep-alive

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