# Audit / log collector (receive side)

An **rsyslog** container that receives logs forwarded by booted diskless hosts
and writes them to durable, per-source-host files. Diskless hosts run on an
immutable erofs root with a **RAM-only volatile overlay**, so their local
`/var/log/audit/audit.log` is lost on every reboot — this gives auditd somewhere
permanent to offload to. It implements the remote-audit-offload that STIG
deviation #6 (`docs/stig-deviations.md`) lists as future hardening.

```
booted host                              serving host
┌───────────────────────────┐           ┌──────────────────────────────┐
│ auditd → audisp-syslog     │  TCP/514  │ audit (this container)        │
│      → rsyslog (forward)   ├──────────►│ rsyslogd → /var/log/remote/   │
│         to ${AUDIT_HOST}   │  syslog   │   <sender-ip>/audit.log       │
└───────────────────────────┘           │   <sender-ip>/messages.log    │
                                         └──────────────────────────────┘
```

## What this provides (the receiver)

- Listens on **TCP/514** (plain syslog). Disk-assisted queue so bursts / brief
  stalls don't drop records.
- Writes per **sender IP** (not the claimed hostname): audit records →
  `audit.log`, everything else → `messages.log`, under
  `./logs/<ip>/` (bind-mounted, inspectable on the host).
- Host-networked, so hosts reach it at `${AUDIT_HOST}` (resolved to the serving
  host by the stack's dnsmasq), matching the boot/NVMe DNS pattern.

Run it with the rest of the stack:

```bash
cd serving
docker compose build audit
docker compose up -d audit
docker compose logs -f audit          # startup + connection messages
tail -F audit-collector/logs/*/audit.log
```

Quick self-test (send a line as if from a host):

```bash
logger -n 127.0.0.1 -P 514 -T -t audispd "test audit record"
ls audit-collector/logs/                 # a 127.0.0.1/ dir appears
```

## What's still needed (the sender — in the image)

This container only **receives**. To make hosts actually send, the hardened
image needs (not yet wired — keep `no per-host state`, use the generic
`${AUDIT_HOST}` name, never a per-host address):

1. **auditd → syslog**: enable the `audisp-syslog` plugin
   (`/etc/audit/plugins.d/syslog.conf`: `active = yes`), so audit events also go
   to the local syslog socket.
2. **rsyslog forward rule**: a drop-in (e.g. `/etc/rsyslog.d/60-fleet-remote.conf`)
   forwarding to the collector with a disk-assisted action queue, so a network
   blip doesn't drop records:

   ```rsyslog
   *.* action(type="omfwd" target="audit.fleet.lab" port="514" protocol="tcp"
              queue.type="LinkedList" queue.fileName="fwdq"
              queue.maxDiskSpace="256m" queue.saveOnShutdown="on"
              action.resumeRetryCount="-1")
   ```
3. Bake `audit.fleet.lab` (the generic name) — DNS resolves it per environment.

Once the sender is wired, flip STIG deviation #6 in `docs/stig-deviations.md`
from "local-only" to "offloading to ${AUDIT_HOST}" and the
`rsyslog_remote_loghost` rule should pass.

## Production hardening (lab simplifications to revisit)

The lab stack is **plaintext TCP**, mirroring the HTTP-boot/no-TLS posture. For
a secured fleet:

- **TLS**: rsyslog `gtls` driver (mutual auth with the boot-infra CA), or
  **RELP + TLS** (`imrelp`/`omrelp`) for guaranteed, acknowledged delivery.
- **Restrict senders** by subnet (`$AllowedSender`) or firewall :514 to the
  boot LAN.
- Add log rotation/retention (logrotate sidecar or rsyslog `outchannel`) and
  ship to long-term storage / SIEM.