F5 Lab 1.13: Fallback Host

As I mentioned on my last article here about configuring priority group activation, there is also an option to redirect the request to an URL when the pool of servers is not available. But please take a note that this feature only available for virtual server which using HTTP profile so only HTTP based application only.

I haven't mention about profiles on my article, basically profile is a container of configured parameter which used by F5 for recognizing and customizing the application behavior. Many profiles can be choose by user to fulfill application use cases by its protocol.

On this lab, I will try to test fallback host feature for MARKETING_WEB virtual server. The fallback host is https://198.51.100.250/.

When all members of MARKETING_WEB_POOL are down, then the HTTP request to the VS will be redirected to fallback host.

Let's dive in:

1. Navigate to Local Traffic => Virtual Servers => Profiles

2. Create new profiles.

3. Configure new profile. To edit the parameter using our defined value, tick the custom box on the right side. Then click "Finished".

• Name: The name of profile
• Proxy Mode: Determines whether the virtual server operates in reverse, explicit, or transparent mode. On this case, I choose Reverse.
• Parent Profile: The parent of the profile. F5 has been create the parent profile and it can't be deleted. Choose HTTP.
• Basic Auth Realm: Indicates the realm that is sent to the client when basic HTTP authentication to the virtual server fails. Leave it blank.
• Fallback Host: Define the URL/host for F5 to redirect the request when all members of the targeted pool are unavailable. I choose to redirect the request to an URL on IP Address 198.51.100.250 It can be another URL like google or other URL.
• Fallback on Error Codes: Indicates the HTTP error codes from server responses that should trigger a redirection to the fallback host. It can be one HTTP error code or multiple error code. In my case, I'm not specified the HTTP error code.

4. Verify newly created profile.

5. Assign newly created HTTP Profile (Client) to MARKETING_WEB virtual server.

6. Test mark down all pool members by changing pool health monitor to UDP.

7. Test access to MARKETING_WEB virtual server again. It will be redirected to fallback host https://198.51.100.250.

If we check deeply to packet capture on external interface of the F5, there's redirection request from the F5 VIP to the client.

HTTP redirection packet sourced from F5 VIP 198.51.100.2 to client 198.51.100.251 with HTTP status code 302: Redirection Found which redirect the HTTP request to new page https://198.51.100.25.

Reference:

• F5-HTTP Profile
• F5-Fallback Host Behavior