add(redirect): how to

* ref to redirects
* how to in NAIS

Co-authored-by: Sindre Rødseth Hansen <[email protected]>
Co-authored-by: Carl Hedgren <[email protected]>

docs/workloads/application/explanations/expose.md

@@ -53,3 +53,12 @@ This allows for routing traffic to only specific parts of your application, or a
 :dart: Learn how to [expose your application with an ingress](../how-to/expose.md).
 
 :books: See the [ingress reference](../reference/ingress.md) for technical details and options.
+
+## Ingress redirects
+
+In some cases, you may want to redirect traffic from one domain to another.
+This can be useful if you have changed the domain of your application, or if you want to redirect users from an old domain to a new one.
+
+:dart: Learn how to [redirect traffic with an ingress](../how-to/redirect.md).
+
+:books: See the [ingress reference](../reference/ingress.md#ingress-redirects) for technical details and options.

docs/workloads/application/how-to/redirect.md

@@ -0,0 +1,55 @@
+---
+tags: [ application, how-to, redirect ]
+---
+
+# Redirect a client
+
+To redirect traffic from one domain to another, you need to define an ingress for the old domain that redirects to the
+new domain, with [`.spec.redirects[]`](../reference/application-spec.md#redirects).
+
+The `redirects` field specifies URL redirects. It is structured as a mapping from a source URL to a target URL.
+
+A successful redirect will return a `302 Moved Temporarily` HTTP status code with location header set to the target URL.
+
+!!! note "Status code"
+    The status code can not be overridden. 
+
+### Structure
+
+```yaml hl_lines="4-5" title=".nais/app.yaml"
+apiVersion: nais.io/v1alpha1
+kind: Application
+spec:
+  ingress:
+    - https://<MY-SUBDOMAIN-OLD>.<ENVIRONMENT-DOMAIN>
+  redirects:
+    - from: https://<MY-SUBDOMAIN-OLD>.<ENVIRONMENT-DOMAIN>
+      to: https://<MY-SUBDOMAIN>.<ENVIRONMENT-DOMAIN>
+```
+
+### Parameters
+
+- **from**: *(string)* The source URL to be redirected. This is the URL where requests originate.
+- **to**: *(string)* The target URL for the redirection. This is the URL where requests will be forwarded.
+
+### Usage Example
+
+```yaml hl_lines="4-5" title=".nais/app.yaml"
+apiVersion: nais.io/v1alpha1
+kind: Application
+spec:
+  ingress:
+    - https://example-old.com
+  redirects:
+    - from: "http://example-old.nais.io"
+      to: "http://example.nais.io"
+```
+
+!!! warning "Redirect restrictions"
+
+    The `from` and `to` URLs must be valid URLs.
+    The `from` URL must be a valid URL that is exposed by the application.
+
+In this example:
+
+- Requests to `http://example-old.nais.io` are redirected to `http://example.nais.io`. 

docs/workloads/application/reference/ingress.md

@@ -25,6 +25,12 @@ spec:
 
 In the example above, only `path1` and `path2` are routed to the application including any sub-paths. All other paths may return a `404` error. Please keep in mind that no path stripping is done as part of the routing and the full path is passed to the application.
 
+## Ingress redirects
+
+[ingress redirects](../explanations/expose.md#ingress-redirects) is a way to perform redirects in NAIS.
+
+Ingress redirects are used to redirect traffic from one domain to another. This can be useful when you want to change the domain of an application or when you want to redirect traffic from an old domain to a new one.
+
 ## Ingress customization
 
 Ingresses are automatically created for your application when you specify them in your [application manifest](application-spec.md).
@@ -267,4 +273,4 @@ Here are some suggestions depending on what http status code you might recieve f
         nginx.ingress.kubernetes.io/proxy-body-size: "256M"     # copied from annotations
         nginx.ingress.kubernetes.io/proxy-buffer-size: "8k"     # copied from annotations
         nginx.ingress.kubernetes.io/proxy-read-timeout: "300"   # copied from annotations
-    ```
+    ```