Question: I am a developer who is used to being able to test and debug code. 

Occasionally I have to make changes to our load balancer configuration. As far as I can see, if I mess this up it could stop the whole site working, but we don't have a way to test it off-line.

How do people test such things? I was hoping there would be some sort of emulator that I could use. Or is it possible to have a second configuration for testing?

I would like to be as confident in the changes I make to the load balancer as I am to the changes I make to my code. Does anyone have a test suite they use for testing their load balancer?

**update**

We are in the process of moving from one back end to another, and we are redirecting users based on the url.

Answer: 
You can get a time (and some functionality) limited virtual edition of LTM that will run in vmware:

<https://www.f5.com/trial/>

Or a test virtual server on the production unit(s) is a good alternative.
Having a test environment is the first answer.

I recommend to automate testing with any HTTP scenario injection tool.

Then comes the question how to keep your environments in sync, and I recommend to give up manual setup on production environment from admin interface.

Proposals to automate BigIP setup the DevOps way are:

* iApp created by F5 <https://clouddocs.f5.com/api/iapps/>
* Ansible modules <https://www.ansible.com/integrations/networks/f5>
* Terraform ressources <https://www.terraform.io/docs/providers/bigip/index.html>
* design your own iApp

Or course applications created from iApp (either from F5 or your own) must be deployed thanks to either Ansible or Terraform.

At the time of writing this, neither Ansible modules nor Terraform ressources cover all BigIP configuration entities yet.