Find a way to add extensions (e.g. callbacks) to moto

[retpolanne]

I have an environment where I want to test the whole EC2 creation flow, from the EC2 api request to a locally-simulated cloud VM with cloud-init.

I created this tool - https://github.com/retpolanne/cloud-vm-sim - that has an API endpoint that receives a userdata and creates a QEMU VM that can reach to this userdata and run cloud-init. I've extended the EC2 code to call this service on the mock and it works nicely :)

However, I wanted this to be cleaner - I don't want moto to have this code as this is useful just for me. I wanted to be able to specify a plugins directory and load them and call whatever is in my plugin before the EC2 response.

[retpolanne]

My code for cloud-sim call is here - 882e010

[bblommers]

Hi @retpolanne! Having an extensions/plugin system is quite the implementation/maintenance effort, and I'm not sure there would be enough usage to justify this.

As an alternative solution:
Would it work to use mock Moto, and extend the functionality that way? That looks like a simpler solution, and achieves the same result:

original_add_instance = InstanceBackend.add_instances
def add_instance_and_run_code(self, image_id, min_count, user_data, security_group_names, **kwargs):
    print("call vm as desired")
    return original_add_instance(self, image_id, min_count, user_data, security_group_names, **kwargs)


@mock_ec2
@mock.patch.object(InstanceBackend, "add_instances", add_instance_and_run_code)
def test_instance_launch_and_terminate():
    client = boto3.client("ec2", region_name="us-east-1")
    # whatever regular test you have...

[retpolanne]

@bblommers thanks! In my case, I'm using moto as a standalone server for apps running in another language, so that wouldn't really work :c

[bblommers]

Ah, I understand. That makes a bit more difficult.

I'll mark it as a feature request, let's see if we can come up with a solution for this.