---
type: reference
description: "Alloy is Grafana's log and telemetry shipper."
tags:
  - infrastructure
timestamp: 2026-10-20
---

# Alloy

Alloy is Grafana's log and telemetry shipper. It replaces Promtail (end of life
as of 2026-03-02, https://grafana.com/docs/loki/latest/send-data/promtail/). It
forwards the host journal — including the rootless Quadlet containers' logs —
to Loki. Unlike its observability siblings it runs as a **root system service on
the host network**, because a rootless container cannot read the journal (see
*Why root* below).

**Host:** Dankclaw (one instance per host) — **UI/health:** 127.0.0.1:12345
(loopback) — **Docs:** https://grafana.com/docs/alloy/latest

## Facts

| Item | Value |
|------|-------|
| Image | `localhost/franksdank/alloy:latest` — built rootless, then mirrored into the root image store by the deployer (a root build fails on DNS in this host's build container) |
| Unit | `dankclaw/observability/quadlet/alloy.container` → system `alloy.service`, installed at `/etc/containers/systemd/` (root manager) |
| Config | `shared/alloy/config.alloy` → `/opt/alloy/config/config.alloy` on every deploy |
| Network | `host` — required so it can reach Loki's `127.0.0.1:3100` publish |
| UI | `--server.http.listen-addr=127.0.0.1:12345` (loopback; nothing off-host reaches it) |
| Inputs | host journal: `system.journal` + `user-*.journal` (root reads both) |
| Output | `http://127.0.0.1:3100/loki/api/v1/push` |
| Boot persistence | `Restart=always`/`RestartSec=10` + `WantedBy=multi-user.target`; boot persistence is the `[Install]` section (generated system units cannot be `enable`d here) |
| Successor to | Promtail (EOL 2026-03-02) |
| Deploy status | root cutover built and tested in-repo (2026-10-20); the **live** instance is still the old rootless unit until `./scripts/deploy.sh dankclaw --service alloy` runs |

## Why root (the load-bearing decision)

A rootless Alloy delivered **zero** lines, silently and with a green health
check. Two independent causes, both proven on the host 2026-10-20:

1. **The journal is not readable by a rootless container.** The files are
   `root:systemd-journal 0640` (`group:adm`, `other::---`). Even bind-mounted, a
   rootless container has no supplementary groups, so opening them returns
   `DENIED`. `loki.source.journal` then sees an empty view and the counter just
   sits at 0 — no error logged.
2. **Container logs live in the *user* journal, not `ctr.log`.** The rootless
   Quadlet containers log via the journald driver into `user-1000.journal`; the
   old file globs (`/var/lib/containers/.../ctr.log`, `/var/log/containers/*.log`)
   point at a root-storage layout that does not exist here.

**Root fixes both at once.** As root the container opens every journal file
under the machine-id directory — `system.journal` *and* `user-1000.journal` —
so a single `loki.source.journal` carries host services and the rootless
containers' logs together. Validated with a throwaway root probe before writing
the unit: **31,825 journal lines read, 26,966 pushed to Loki in 20 s, zero
drops**, and Loki's label set went from empty to populated.

### The two mounts that make it work

- **`/etc/machine-id` (ro) — load-bearing.** `sd_journal` locates the journal
  directory by the *local* machine id. Without it the container opens nothing and
  the journal source reads exactly 0 lines — silently, health green. This single
  mount is the whole difference between a working and an empty pipeline; do not
  remove it. (A root probe without it reads 0; with it, 31,825.)
- **`Network=host`.** Loki publishes `127.0.0.1:3100` (loopback only). No bridge
  container — rootless or root — can reach the host's loopback, so Alloy must
  share the host network to push to `127.0.0.1:3100`. Consequence: the UI binds
  `127.0.0.1` directly (no `PublishPort`), so it stays loopback-only as before.

## Configuration

`shared/alloy/config.alloy` is the source of truth — one `loki.source.journal`
(labelled `job="systemd-journal"`) forwarding to the loopback `loki.write`
endpoint. There is deliberately **no** container-file source: container stdout is
in the journal.

## Volumes

| Container path | Host path |
|----------------|-----------|
| `/etc/alloy` | `/opt/alloy/config` (ro) |
| `/etc/machine-id` | host machine id (ro) — **required** |
| `/run/systemd/journal/socket` | host journald socket (ro) |
| `/var/log/journal` | persistent journal files (ro) |
| `/run/log/journal` | runtime journal files (ro) |

## The UI stays on loopback

Alloy 1.x refuses to configure the `ui` service from a config block, so the UI
address is set on the command line instead. Under the old rootless unit that
meant `0.0.0.0` inside the container plus a published `127.0.0.1:12345`; under
`Network=host` the listen-addr is `127.0.0.1:12345` directly — the host's
loopback, reachable from the host and from nothing off-host. Alloy has no
authentication, which is exactly why it is never published wider. The homepage
card and the deploy health gate both dial `http://127.0.0.1:12345/-/healthy`.

## Gotchas

- **No `/etc/machine-id` mount ⇒ silent zero.** The health check still passes.
  This is the failure mode that hid the broken pipeline; check
  `loki_source_journal_target_lines_total` and the Loki label query, never
  `/healthy`.
- **`After=loki.service` is gone.** Alloy is on the system manager; Loki is a
  rootless user unit — a system unit cannot order against a user unit. Alloy
  retries its push until Loki answers, so ordering is unnecessary.
- **The image must be in the ROOT store.** The deployer builds rootless and
  mirrors (`mirror_image_to_root`); a `Pull=never` root quadlet with only a
  rootless tag fails at create.
- One Alloy per host; do not run a single instance that tries to reach both
  hosts' logs.

## See Also

- [[Loki]] — the log backend
- [[Observability]] — the full stack, including what is still unconfigured