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docs(alloy): document the root journal-read cutover

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Alloy page rewritten to the shipped root design (why root, the two
mounts that make it work, deploy-pending status); Observability current
state marks the log pipeline fixed-in-code, awaiting deploy.
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2026-10-20 19:50:15 -07:00
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serverAppConfigs-docs/Infrastructure/Alloy.md
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description: "Alloy is Grafana's log and telemetry shipper."
tags:
- infrastructure
timestamp: 2026-09-11
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 is wired to forward container and journal logs to Loki, and every unit in the path is healthy — but as of 2026-10-18 it is delivering **zero** log lines. See "Delivery state" below.
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) — **Port:** 12345 (loopback) — **Docs:** https://grafana.com/docs/alloy/latest
**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 | `franksdank/alloy:latest` (local build: upstream + a static busybox for the healthcheck) |
| Published | `127.0.0.1:12345` → 12345 (its own UI/health port) |
| Unit | `dankclaw/observability/quadlet/alloy.container` → `alloy.service` |
| Config | `shared/alloy/config.alloy`, installed to `/opt/alloy/config/config.alloy` on every deploy (`scripts/deploy-remote.sh:281-284`) |
| Inputs | host journald socket, podman container logs, `/var/log` |
| Output | `http://loki:3100/loki/api/v1/push` (`shared/alloy/config.alloy:13-17`) |
| Successor to | Promtail (EOL 2026-03-02, https://grafana.com/docs/loki/latest/send-data/promtail/) |
| Boot persistence | `Restart=always`/`RestartSec=10` + `WantedBy=default.target` (`dankclaw/observability/quadlet/alloy.container:58-63`); installed at `~/.config/containers/systemd/alloy.container`, reporting `generated` + `active` (`systemctl --user is-enabled|is-active alloy` 2026-10-18) |
| Delivery | **Configured and healthy, currently delivering zero data** — see "Delivery state" |
| 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 Alloy and not Promtail
## Why root (the load-bearing decision)
Promtail reached end-of-life on 2026-03-02 and Grafana Labs directs new installs to Alloy. This stack uses Alloy from day one: no Promtail config or unit has ever existed in this repository (`git log -S promtail` over the whole history returns no commit that added one; the compose-era service of the same name was already Alloy — `dankclaw/observability/quadlet/alloy.container:6-7`).
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:
- Reads journald logs from the host's `/run/systemd/journal/socket`, labelled `job="systemd-journal"` (`shared/alloy/config.alloy:20-26`).
- Reads container logs from two globs: `/var/lib/containers/storage/overlay-containers/*/userdata/ctr.log` (`job="podman"`) and `/var/log/containers/*.log` (`job="containers"`) (`config.alloy:29-35`).
- Forwards everything to `http://loki:3100/loki/api/v1/push` by container name on `dankclaw_default` (`config.alloy:13-17`).
`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` |
| `/run/systemd/journal/socket` | host journald socket (read-only) |
| `/var/log` | host logs (read-only) |
| `/var/lib/containers` | podman storage (read-only) |
| `/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 port is published on purpose
## The UI stays on loopback
Alloy's UI listens on the container's own `127.0.0.1:12345` by default, and Alloy 1.x refuses to configure the `ui` service from a config block ("service ui does not support being configured", `shared/alloy/config.alloy:8-10`). Under compose that meant **no reachable health endpoint at all**: the homepage status card for alloy read `down` continuously and a deploy had nothing to wait on. The unit therefore passes `--server.http.listen-addr=0.0.0.0:12345` (`dankclaw/observability/quadlet/alloy.container:46`) and publishes `127.0.0.1:12345` (`alloy.container:47`, confirmed by `ss -ltnp` 2026-10-18) — same posture as the other three: reachable from the host and from Caddy's network, and from nothing off-host. Alloy has no authentication, which is exactly why it is not published wider. The homepage card probes that same loopback port (`shared/homepage/services.json:233`).
## Delivery state (2026-10-20): healthy, shipping nothing
The unit is `active`, the container reports `healthy`, the log says `Alloy is
ready`, and the pipeline carries no data at all.
**Root cause, proven: a rootless container cannot read the host journal.** The
journal files are `root:systemd-journal 0640` (with `group:adm`, `other::---`).
`/var/log` is bind-mounted so the files are *visible*, but a rootless container
spawns with no supplementary groups, so it is denied. Proven directly:
`podman run --rm -v /var/log/journal:/var/log/journal:ro busybox cat
/var/log/journal/*/system.journal` → `DENIED`. `loki.source.journal` opens via
`sd_journal_open`, so it silently sees an empty view — no error logged, counter
frozen at `loki_source_journal_target_lines_total 0` (`system.journal` and
`user-1000.journal` are both present and non-trivial, 2026-10-20).
**Second, independent gap:** the rootless Quadlet containers log to the *user*
journal (`user-1000.journal`), and `loki.source.journal` reads the *system*
journal only — a fixed system read would still miss them. Container stdout is
not in a `ctr.log` here either: the file globs point at root storage
(`/var/lib/containers/storage/.../ctr.log`, `/var/log/containers/*.log`) that
rootless does not use, refused at start with `stat …: permission denied` / `no
such file or directory`, `loki_source_file_files_active_total 0`.
Downstream: Loki holds zero streams (`GET /loki/api/v1/labels` → no `data`) —
see [[Loki]].
**Closing it is a permission/architecture decision, not a config edit.** The
unit, config and push endpoint are correct as written; rootless Podman simply
cannot grant the journal group. The viable shapes: run Alloy as a *system*
service (root, in `adm`/`systemd-journal`) instead of a rootless Quadlet; grant
the container's mapped uid journal read via a tmpfiles/ACL rule; or have
journald forward to a path the container can read. Each trades rootless posture
for reach — decide deliberately. Re-check `loki_source_journal_target_lines_total`
and the Loki label query to confirm a fix, never `/healthy`: health is exactly
what hides this failure.
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
- The journald socket mount is required for journal scraping.
- Container log paths differ between docker (`/var/lib/docker/containers`) and podman (`/var/lib/containers/storage/...`); point the config at the right one per host.
- One Alloy per host; do not run a single instance that tries to reach both hosts' logs.
- The unit `Wants=`/`After=` `loki.service`: without a reachable Loki the write client fails and the pipeline backs up.
- **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
serverAppConfigs-docs/Infrastructure/Observability.md
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installed from `shared/grafana/provisioning/`. The Loki datasource is how
you read logs: Loki has no web UI of its own, so Grafana Explore is the
human surface (the guarded `loki.franksdank.cloud` vhost serves only the API).
* **Logs: configured, empty.** Alloy ships zero lines and Loki holds zero
streams (`GET /loki/api/v1/labels` returns no label names; no chunk files on
disk). The cause is source-side access, now proven, not a config bug: a
rootless container cannot read the journal files (`system.journal` is
`root:systemd-journal 0640`/`adm` and a rootless read of it returns DENIED),
and the container-log globs point at a root-storage path that does not exist
under rootless. Closing it is a permission/architecture decision, not an
edit — see [[Alloy]] → Delivery state and [[Loki]] → Contents.
* **Logs: fixed in code, awaiting deploy.** The pipeline shipped nothing because
a rootless Alloy cannot read the `0640` journal files, and the container-log
globs point at a root-storage layout that does not exist here. The fix is built
and tested in-repo (2026-10-20): Alloy is now a **root system service on
`Network=host`**, reading `system.journal` + `user-*.journal` and pushing to
Loki's `127.0.0.1:3100` loopback publish — a throwaway root probe read 31,825
lines and pushed 26,966 with zero drops. The **live** instance is still the old
rootless unit until `deploy.sh dankclaw --service alloy` runs. Detail in
[[Alloy]] → Why root; Loki's store state in [[Loki]] → Contents.
* **Not configured:** no blackbox exporter (the structural downs have no real
uptime signal) and no Alertmanager vhost. The log pipeline is provisioned
but carries no data (see *Logs* above).
uptime signal) and no Alertmanager vhost. The log pipeline's fix is in code but
not yet deployed (see *Logs* above).
## Citations