Merge pull request 'traefik: add log rotation for access.log / traefik.log' (#23) from fix/traefik-log-rotation into main

Reviewed-on: #23
https://ai.bryanmail.net/c/5d375026-71a6-444a-a406-55fd55ad1f73

traefik/logrotate/README.md

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+# Traefik Log Rotation
+
+## Why this exists
+
+`traefik/traefik.yaml` runs Traefik with:
+- `--accesslog.filePath=/traefik/logs/access.log`
+- `--log.filePath=/traefik/logs/traefik.log`
+- `--log.level=DEBUG`
+
+Neither file has any built-in rotation -- Traefik has no native rotate-on-size
+nor a SIGUSR1/reopen handler. Docker's `json-file` log-driver rotation
+(`max-size`/`max-file`) only applies to stdout, not to files Traefik writes
+directly via `--accesslog.filePath`/`--log.filePath`. Result: `access.log` grew
+to **~15.5GB unrotated** before this was caught, on a CephFS volume
+(`/volume1/docker-root`) already at 82-84% used. Both the disk pressure and
+the ongoing write latency of appending to a 15GB file on a network filesystem
+on every request through Traefik were flagged as a real risk factor during
+troubleshooting (Uptime Kuma WebSocket flapping investigation, Sep 2026).
+
+**Note:** during that investigation, the actual root cause of the WebSocket
+flapping turned out to be Uptime Kuma monitor misconfigurations (a Postgres
+monitor throwing a null-reference error, and several monitors failing TLS
+validation against self-signed/internal-IP certs) -- not this log file. This
+rotation fix is still worth doing as general disk/IO hygiene, just not
+causally tied to that incident.
+
+## Architecture constraint this design accounts for
+
+`traefik_reverse-proxy` runs Swarm *`mode: global`* -- one instance on **each**
+of docker-1, docker-2, docker-3. All three write to the **same physical file**
+via the shared CephFS bind mount `/volume1/docker/traefik -> /traefik`
+(identical mount, visible identically from any node). That rules out:
+
+- **Signal-based rotation** (classic `create` + `postrotate` sending SIGUSR1):
+  Traefik doesn't implement a reopen signal, and even if it did, you'd need to
+  signal 3 separate per-node containers in lockstep.
+- **Running logrotate on just one node**: works until that node is down, then
+  rotation silently stops with no alert.
+
+So this setup uses:
+1. **`copytruncate`** (see `traefik-logs.conf`) -- all three Traefik processes
+   keep writing to the same inode, no signaling needed. Tradeoff: a few log
+   lines written in the exact copy/truncate instant can be lost -- fine for
+   diagnostic logs.
+2. **Cron on all three nodes**, coordinated via a shared `flock` + shared
+   logrotate state file, both also on the CephFS mount (see
+   `traefik-logrotate.sh`). Whichever node's cron fires first grabs the lock,
+   rotates if due, and updates the shared state so the other two nodes' cron
+   runs see it's already done. No single node is a rotation SPOF.
+3. **Size-triggered** (`size 250M`) rather than calendar-triggered (`daily`) --
+   this file can grow fast under bursts (see incident background above); a
+   purely daily interval would still let it balloon between runs. Cron checks
+   every 15 minutes, so it cannot grow much past the 250M threshold in practice.
+
+## Install (one-time, per node)
+
+Must run on **all three** docker LXCs -- this is host-level cron/logrotate
+config, not something `stack-deploy.sh` can reach (it only touches Swarm
+services, not host cron jobs).
+
+```bash
+# On each of docker-1 (192.168.4.31), docker-2 (192.168.4.32), docker-3 (192.168.4.33):
+ssh root@<192.168.4.31|.32|.33>
+cd /volume1/docker/compose-files
+bash deploy/git-guard.sh         # confirm sync first, as always
+sudo bash traefik/logrotate/install.sh
+```
+
+Verify on each node:
+```bash
+cat /etc/cron.d/traefik-logrotate
+logrotate -d /etc/logrotate.d/traefik-logs   # dry-run, confirms syntax
+```
+
+## Bootstrapping -- shrinking the *existing* oversized log file
+
+**Not done automatically by `install.sh`.** The new size-triggered config only
+prevents *future* unbounded growth -- it won't touch the current 15.5GB file
+until the next time it crosses 250M (i.e. never, since it's already well past
+that and logrotate only acts on crossing the threshold going forward from its
+recorded size at last check).
+
+`copytruncate` always copies the full current file before truncating it --
+that's inherent to how it works, not a bug. Forcing a rotation of the current
+15.5GB file would momentarily need roughly another 15-GB-sized chunk of free
+space -- and `/volume1/docker-root` only had **~14G free** at last check.
+Doing this blindly could tip the volume to 100% mid-operation.
+
+**Recommended manual step (operator-run, on any one node -- it's the same
+CephFS file from all three)**: these are diagnostic access/debug logs, not
+something worth preserving in full, so just truncate directly rather than
+compress-then-truncate:
+
+```bash
+# Optional: keep a small tail sample for reference before truncating
+tail -c 50000000 /volume1/docker/traefik/logs/access.log > \
+  /volume1/docker/traefik-access-log-archive-$(date +%Y%m%d).log
+
+# Then truncate in place (safe -- Traefik's existing file handles on all 3
+# nodes stay valid, same as copytruncate's own mechanism):
+: > /volume1/docker/traefik/logs/access.log
+: > /volume1/docker/traefik/logs/traefik.log
+
+# Confirm:
+df -h /volume1/docker-root
+ls -la /volume1/docker/traefik/logs/
+```
+
+After this one-time bootstrap, the cron+logrotate setup keeps it bounded
+(rotates at 250M, keeps 48 compressed generations, prunes anything over 14
+days old) going forward without needing any further manual intervention.
+
+## Related, NOT included in this change (follow-up to consider separately)
+
+`traefik.yaml` currently runs `--log.level=DEBUG` -- verbose debug logging in
+production, which is a meaningful contributor to how fast these files grow.
+Lowering to `INFO` would reduce volume significantly but requires a real
+modification + redeploy of the high-blast-radius `traefik` stack (all
+HTTP/HTTPS routing depends on it), so it's intentionally left out of this PR
+and should be its own reviewed change if wanted.

traefik/logrotate/install.sh

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+#!/usr/bin/env bash
+# One-time installer for Traefik log rotation.
+#
+# MUST be run manually, once, on EACH of docker-1, docker-2, docker-3.
+# This is intentionally NOT part of stack-deploy.sh / the Woodpecker
+# pipeline: it installs a host-level cron.d entry and /etc/logrotate.d
+# config, and `docker stack deploy` has no mechanism to reach outside the
+# Swarm/container boundary onto host cron. See README.md for why this needs
+# to run on all three nodes.
+#
+# Usage (from a checkout of this repo, on each node):
+#   sudo bash traefik/logrotate/install.sh
+set -euo pipefail
+
+if [[ $EUID -ne 0 ]]; then
+  echo "Run as root (sudo)." >&2
+  exit 1
+fi
+
+REPO_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
+
+echo "Installing logrotate config..."
+install -m 0644 "$REPO_DIR/traefik-logs.conf" /etc/logrotate.d/traefik-logs
+
+echo "Installing rotation wrapper..."
+install -m 0755 "$REPO_DIR/traefik-logrotate.sh" /usr/local/sbin/traefik-logrotate.sh
+
+echo "Installing cron.d schedule (every 15 minutes)..."
+cat > /etc/cron.d/traefik-logrotate << 'EOF'
+# Managed by homelab/compose-files traefik/logrotate/install.sh -- do not
+# hand-edit; update traefik/logrotate/*.{conf,sh} in Gitea and re-run
+# install.sh instead.
+*/15 * * * * root /usr/local/sbin/traefik-logrotate.sh
+EOF
+chmod 0644 /etc/cron.d/traefik-logrotate
+
+echo "Verifying logrotate config syntax..."
+logrotate -d /etc/logrotate.d/traefik-logs
+
+echo "Done. First rotation check runs on the next cron tick (up to 15 min)."
+echo "This only rotates going forward once the file crosses the size threshold."
+echo "To shrink the EXISTING already-large log file, see README.md -- that is"
+echo "a separate, deliberate manual step (not done by this script) because it"
+echo "needs disk headroom awareness first."

traefik/logrotate/traefik-logrotate.sh

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+#!/usr/bin/env bash
+# Wrapper invoked by cron on docker-1/docker-2/docker-3 to rotate the shared
+# Traefik access/error logs (see traefik-logs.conf for the "full why").
+#
+# Because /volume1/docker/traefik/logs is the SAME physical CephFS path on
+# all three nodes, and cron on all three nodes runs this independently, we
+# use a shared flock (also on the CephFS mount, so it's visible cluster-wide)
+# to guarantee only one node actually executes logrotate at a time, and a
+# SHARED state file so whichever node runs it knows the true last-rotated
+# time regardless of which node rotated it last. If a node is down, the
+# other two still cover the schedule -- none of this relies on a specific
+# node being up.
+set -euo pipefail
+
+LOCK_DIR="/volume1/docker/traefik/logrotate-state"
+LOCK_FILE="$LOCK_DIR/rotate.lock"
+STATE_FILE="$LOCK_DIR/status"
+CONF_FILE="/etc/logrotate.d/traefik-logs"
+
+mkdir -p "$LOCK_DIR"
+touch "$STATE_FILE"
+
+exec 200>"$LOCK_FILE"
+if ! flock -n 200; then
+  # Another node already holds the lock this cycle -- normal, not an error.
+  exit 0
+fi
+
+/usr/sbin/logrotate -s "$STATE_FILE" "$CONF_FILE"

traefik/logrotate/traefik-logs.conf

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+# Traefik access/error log rotation
+#
+# CONTEXT: traefik_reverse-proxy runs in Swarm `mode: global` (traefik.yaml),
+# meaning one instance runs on EACH of docker-1/docker-2/docker-3. All three
+# write to the SAME physical file via the shared CephFS bind mount
+# /volume1/docker/traefik/logs -> /traefik (identical path from any node --
+# see infra context: /volume1/docker is a shared CephFS mount).
+#
+# `copytruncate` is REQUIRED here (not the default create+signal approach):
+# Traefik has no SIGUSR1/SIGHUP "reopen log file" handling, and even if it
+# did, coordinating a reopen signal across 3 independent per-node containers
+# writing to one shared inode is unnecessary complexity. copytruncate keeps
+# every writer's existing file descriptor valid (truncates in place) so all
+# three Traefik processes keep appending to the same inode with zero
+# signaling. Tradeoff: a handful of log lines written in the exact
+# copy/truncate instant can be lost -- acceptable for diagnostic access/error
+# logs, not used for anything transactional.
+#
+# Size-triggered (not calendar-triggered) on purpose: this file can grow fast
+# under bursts (see incident that prompted this -- 15.5GB accumulated with
+# --log.level=DEBUG set). `size` is checked every time the wrapper script runs
+# (cron, every 15 minutes -- see install.sh), so it cannot balloon unbounded
+# between checks the way a plain `daily` interval would.
+#
+# Installed via install.sh on ALL THREE docker LXCs (docker-1, docker-2,
+# docker-3) -- see README.md. This is a HOST-level cron/logrotate config,
+# outside the Woodpecker/stack-deploy.sh pipeline (docker stack deploy has no
+# mechanism to touch host cron), so it must be applied manually once per node,
+# not via a stack redeploy.
+
+/volume1/docker/traefik/logs/*.log {
+    size 250M
+    rotate 48
+    maxage 14
+    compress
+    delaycompress
+    missingok
+    notifempty
+    copytruncate
+    dateext
+    dateformat -%Y%m%d-%H%M%S
+    su root root
+}