Allow Existing ALB to be used

I have been following along and using the ALB events and provisioning PR #1807 that was just merged in by @PeteW and @youcandanch.

I was using those changes and integrating my Lambda’s into an existing ALB provisioned via terraform

I have some proposed zappa settings and code changes to allow the use of an existing ALB, multiple Zappa projects can then be deployed onto the same ALB

When using an existing ALB, there is an assumption of the Listener existing also, So instead of creating these resources Listener Rules need to be created https://boto3.amazonaws.com/v1/documentation/api/latest/reference/services/elbv2.html#ElasticLoadBalancingv2.Client.create_rule

These can be defiend in the zappa_settings like :

"alb_vpc_config": {
    "LoadBalancerArn": "arn:aws:acm:us-east-1:[your-account-id]:loadbalancer/app/[alb-name]/[f851177b4d4eb840]",
    "alb_listener_rule_conditions": {
        "Field": "path-pattern|host-header",
        "Values": ["api/*"|"api.example.com"]
    },
    "alb_listener_rule_priority": 1
}

[alex-lampila]

This feature is also critical for me. Another related feature would be to expose settings to allow invocation without Zappa managing any of the ALB resources. In otherwords, Zappa would add lambda:InvokeFunction permission, but would not touch the ALB resources. The rationale for this would be centralized management of the ALB, listeners, and rules.

Is there anything that can be done to help move this PR forward? I am happy to help.

[ssilverm]

Bump for us as well.