Converting Citrix NetScaler Transform Policy to F5 BIG-IP LTM

Hiii Hamza

 

if i understand the policy of Citrix 

Requests to example.com are internally redirected to local.com, but the client continues to see example.com as the domain. Similarly, responses from local.com are transformed to appear as if they are coming from example.com. The cookies retain the original domain example.com, ensuring that clients do not experience any inconsistencies when accessing the service.

you have 2 ways, iRule or policy

 

example of iRule

when HTTP_REQUEST {
    if {[HTTP::host] contains "example.com"} {
        HTTP::header replace Host "local.com"
        set new_uri [string map {"example.com" "local.com"} [HTTP::uri]]
        HTTP::uri $new_uri
    }
}

when HTTP_RESPONSE {
    if {[HTTP::header value "Location"] contains "local.com"} {
        set new_location [string map {"local.com" "example.com"} [HTTP::header value Location]]
        HTTP::header replace Location $new_location
    }

    if {[HTTP::header exists "Set-Cookie"] && [HTTP::header value "Set-Cookie"] contains "local.com"} {
        set new_cookie [string map {"local.com" "example.com"} [HTTP::header value "Set-Cookie"]]
        HTTP::header replace "Set-Cookie" $new_cookie
    }
}

 

 

 

 

 

 

 

 

This seems like a good gen AI task, and it's seemed to output a realistic answer. You'll have to test this of course, but it should get you close.

 

Me <explain the task>.

 

GPT-4o:

Let's break down the transform rule and explain it from the perspective of HTTP RFC 2616, which defines the HTTP/1.1 protocol.

### Transform Profile and Policy

1. **Transform Profile and Policy Creation:**
   - `add transform profile x_transform_profile`
   - `add transform policy x_policy true x_transform_profile`

   This part creates a transform profile named `x_transform_profile` and a transform policy named `x_policy` that is always true (`true` condition). The policy is associated with the transform profile `x_transform_profile`.

### Transform Action

2. **Adding and Setting Transform Action:**
   - `add transform action x_action x_transform_profile 10`
   - `set transform action x_action -priority 10 -reqUrlFrom "example.com/(.*)" -reqUrlInto "local.com/$1" -resUrlFrom "local.com/(.*)" -resUrlInto "example.com/$1" -cookieDomainFrom example.com -cookieDomainInto example.com`

   This part adds a transform action named `x_action` to the transform profile `x_transform_profile` with a priority of 10. Then, it sets the details of the transform action. Let's break down these details:

### URL Transformation

3. **Request URL Transformation:**
   - `-reqUrlFrom "example.com/(.*)" -reqUrlInto "local.com/$1"`

   This rule states that for incoming HTTP requests, any URL matching the pattern `example.com/(.*)` will be transformed into `local.com/$1`. The `(.*)` is a regular expression that matches any sequence of characters, and `$1` refers to the first captured group in the regular expression.

   - For example, if the incoming request URL is `http://example.com/path/to/resource`, it will be transformed into `http://local.com/path/to/resource`.

4. **Response URL Transformation:**
   - `-resUrlFrom "local.com/(.*)" -resUrlInto "example.com/$1"`

   This rule states that for outgoing HTTP responses, any URL matching the pattern `local.com/(.*)` will be transformed into `example.com/$1`.

   - For example, if the outgoing response URL is `http://local.com/path/to/resource`, it will be transformed into `http://example.com/path/to/resource`.

### Cookie Domain Transformation

5. **Cookie Domain Transformation:**
   - `-cookieDomainFrom example.com -cookieDomainInto example.com`

   This rule specifies that cookies with the domain `example.com` should keep their domain as `example.com`. This seems redundant in this context, as it doesn't appear to change the cookie domain, but it might be part of a larger set of rules or a template where domains could vary.

### Summary

From an HTTP RFC 2616 perspective, this transform rule effectively:

- Modifies incoming request URLs from the format `http://example.com/...` to `http://local.com/...`.
- Modifies outgoing response URLs from the format `http://local.com/...` back to `http://example.com/...`.
- Ensures that cookies with the domain `example.com` remain unchanged.

This transformation can be useful in scenarios where a reverse proxy or load balancer is used to internally route requests to a different domain (`local.com`) while keeping the external-facing domain (`example.com`) consistent for the client. It ensures that users interacting with `example.com` see URLs and cookies that match this domain, even though the backend systems see and handle `local.com` URLs.

 

---------------

me:

Now we understand the policy. Take off your Netscaler hat and put on a BIG-IP hat and you are now an experienced F5 iRules network administrator. 
Write F5 BIG-IP iRules to implement the same thing as the Netscaler rules above.

---------------

GPT-4o:

We'll create an iRule that modifies the request URLs from example.com to local.com and the response URLs from local.com back to example.com. We'll also ensure that cookies with the domain example.com remain unchanged.

when HTTP_REQUEST {
    # Transform incoming request URLs
    if { [HTTP::host] equals "example.com" } {
        set new_url [string map {"example.com" "local.com"} [HTTP::uri]]
        HTTP::uri $new_url
    }
}

when HTTP_RESPONSE {
    # Transform outgoing response URLs
    if { [HTTP::header "Location"] ne "" } {
        set location_header [HTTP::header "Location"]
        if { $location_header contains "local.com" } {
            set new_location [string map {"local.com" "example.com"} $location_header]
            HTTP::header replace "Location" $new_location
        }
    }

    # Ensure cookies with the domain example.com remain unchanged
    foreach cookie [HTTP::cookie names] {
        if { [HTTP::cookie domain $cookie] equals "example.com" } {
            HTTP::cookie domain $cookie "example.com"
        }
    }
}

 

Explanation

1. HTTP_REQUEST Event:
   • The HTTP_REQUEST event is triggered when an HTTP request is received.
   • We check if the Host header equals example.com.
   • If it does, we modify the request URI by replacing example.com with local.com.
   • The HTTP::uri command is used to set the new request URI.
2. HTTP_RESPONSE Event:
   • The HTTP_RESPONSE event is triggered when an HTTP response is being sent.
   • We check if the Location header is present and contains local.com.
   • If it does, we replace local.com with example.com in the Location header.
   • The HTTP::header replace command is used to set the new Location header.
3. Cookie Domain Transformation:
   • We iterate over all cookies in the response.
   • If a cookie has the domain example.com, we ensure its domain remains example.com using the HTTP::cookie domain command.