# l1-alb — Application Load Balancer primitive (multi-resource L1)

An L1 module for an Application Load Balancer (load balancer + target
group + listener). Substrate-agnostic (the IR types are
`aws:elbv2:loadbalancer`, `aws:elbv2:listener`, `aws:elbv2:targetgroup`,
not Terraform resource types). This is a multi-resource L1: the
interface declares the group's inputs/outputs plus a `resources` array
listing the IR types it emits. The IR instance (Phase 14/15) will have
multiple `resources` entries all with `module: "l1-alb@1.0.0"`.

## Interface (the IR-typed contract)

See `interface.json`: inputs `name` (string), `subnets` (string,
comma-separated, ref to l1-vpc), `security_group` (string), `port`
(number, default 80), `protocol` (string, default "HTTP"), `region`
(string); outputs `lb_arn` (arn) + `listener_arn` (arn) +
`target_group_arn` (arn); no NFRs.

The `resources` array lists the emitted IR types:

- `aws:elbv2:loadbalancer` — application load balancer in the VPC
  subnets.
- `aws:elbv2:targetgroup` — target group for the ECS service tasks.
- `aws:elbv2:listener` — listener forwarding the LB port to the target
  group.

## IR → Terraform mapping (performed by the adapter)

The Terraform adapter (`adapters/terraform/adapter.py`) translates each
emitted IR resource to Terraform:

| IR | Terraform |
|----|-----------|
| `resource.type = aws:elbv2:loadbalancer` | `resource "aws_lb" "<id>" { ... }` |
| `resource.inputs.name` | `name = <value>` arg |
| `resource.inputs.subnets` | `subnets = [<value>]` arg (comma-split) |
| `resource.inputs.security_group` | `security_groups = [<value>]` arg (comma-split) |
| `resource.outputs.lb_arn` | `output "lb_arn" { value = aws_lb.<id>.id }` |
| `resource.type = aws:elbv2:targetgroup` | `resource "aws_lb_target_group" "<id>" { ... }` |
| `resource.inputs.port` | `port = <value>` arg |
| `resource.inputs.protocol` | `protocol = <value>` arg |
| `resource.outputs.target_group_arn` | `output "target_group_arn" { value = aws_lb_target_group.<id>.arn }` |
| `resource.type = aws:elbv2:listener` | `resource "aws_lb_listener" "<id>" { ... }` |
| `resource.inputs.lb_arn` | `load_balancer_arn = <value>` arg (identity) |
| `resource.inputs.port` | `port = <value>` arg |
| `resource.inputs.protocol` | `protocol = <value>` arg |
| `resource.outputs.listener_arn` | `output "listener_arn" { value = aws_lb_listener.<id>.id }` |

The adapter is a thin layer (ARCHITECTURE.md §12.2); it does not own L1
content — it only translates.

## Versioning (W3.D)

`1.0.0` — interface MAJOR, behavior MINOR, lifecycle PATCH. MAJOR bumps
require a new registry entry (immutable publication); old entries enter
a 12-month deprecation window.