# checker-alias

CNAME / DNAME / ALIAS chain checker for [happyDomain](https://www.happydomain.org/).

Walks the alias chain of a name, validates hop count, TTLs, target
resolvability, apex coexistence (RFC 1912 §2.4, RFC 1034 §3.6.2,
RFC 2181 §10.1), DNAME substitutions, and DNSSEC signing of the CNAME
RRset.

## Usage

### Standalone HTTP server

```bash
# Build and run
make
./checker-alias -listen :8080
```

The server exposes:

- `GET /health`: health check
- `POST /collect`: collect alias observations (happyDomain external checker protocol)

### Docker

```bash
make docker
docker run -p 8080:8080 happydomain/checker-alias
```

### happyDomain plugin

```bash
make plugin
# produces checker-alias.so, loadable by happyDomain as a Go plugin
```

The plugin exposes a `NewCheckerPlugin` symbol returning the checker
definition and observation provider, which happyDomain registers in its
global registries at load time.

### Versioning

The binary, plugin, and Docker image embed a version string overridable
at build time:

```bash
make CHECKER_VERSION=1.2.3
make plugin CHECKER_VERSION=1.2.3
make docker CHECKER_VERSION=1.2.3
```

### happyDomain remote endpoint

Set the `endpoint` admin option for the alias checker to the URL of the
running checker-alias server (e.g., `http://checker-alias:8080`).
happyDomain will delegate observation collection to this endpoint.

## Options

| Id                        | Type | Default | Description                                                                 |
|---------------------------|------|---------|-----------------------------------------------------------------------------|
| `maxChainLength`          | uint | `8`     | Above this number of hops the chain is reported as critical.                |
| `minTargetTTL`            | uint | `60`    | Hops with a TTL below this threshold are flagged as a warning.              |
| `requireResolvableTarget` | bool | `true`  | When enabled, a final target with no A/AAAA is critical (otherwise warning).|
| `allowApexCNAME`          | bool | `false` | When enabled, a CNAME at apex is only a warning (RFC 1912 forbids it).      |
| `recognizeApexFlattening` | bool | `true`  | Recognize provider-side ALIAS/ANAME flattening as informational.            |

## Rules

Each rule emits a finding code. Severity can be affected by the options above.

| Code | Default severity | Condition |
|------|-----------------|-----------|
| `apex_lookup` | critical | Zone apex (SOA) cannot be located for the queried name. |
| `chain_loop` | critical | A CNAME/DNAME cycle is detected in the resolution chain. |
| `chain_length` | critical | The chain exceeds `maxChainLength` hops. |
| `chain_query_error` | warning | A DNS query fails while walking the chain (network error, timeout). |
| `chain_rcode` | critical (mid-chain) / warning (final) | A non-NOERROR response code is encountered during chain resolution or the final A/AAAA lookup. |
| `hop_ttl` | warning | A CNAME/DNAME hop has a TTL below `minTargetTTL`. |
| `cname_at_apex` | critical / warning with `allowApexCNAME` | A CNAME exists at the zone apex, conflicting with SOA/NS (RFC 1912 §2.4). |
| `apex_flattening` | info | A/AAAA records coexist with SOA/NS at the apex without a CNAME, provider-side ALIAS/ANAME flattening. Only reported when `recognizeApexFlattening` is enabled. |
| `cname_coexistence` | critical / warning with `allowApexCNAME` at apex | Other RRsets (beyond A/AAAA) coexist at a CNAME owner, violating RFC 1034 §3.6.2 / RFC 2181 §10.1. |
| `cname_dnssec` | critical | The zone is DNSSEC-signed but the CNAME RRset at the queried name lacks an RRSIG. |
| `target_resolvable` | critical / warning with `requireResolvableTarget=false` | The final target of the chain has no A or AAAA record. |
| `multiple_records` | critical | An owner in the chain carries more than one CNAME/DNAME record (malformed). |

## License

Licensed under the **MIT License** (see `LICENSE`).