docs: add Loki improvements plan
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Covers retention policy, limits config, Promtail label improvements (tier/role/level), and journal PRIORITY extraction. Also adds Alloy consideration to VictoriaMetrics migration plan. Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
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docs/plans/loki-improvements.md
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docs/plans/loki-improvements.md
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# Loki Setup Improvements
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## Overview
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The current Loki deployment on monitoring01 is functional but minimal. It lacks retention policies, rate limiting, and uses local filesystem storage. This plan evaluates improvement options across several dimensions: retention management, storage backend, resource limits, and operational improvements.
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## Current State
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**Loki** on monitoring01 (`services/monitoring/loki.nix`):
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- Single-node deployment, no HA
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- Filesystem storage at `/var/lib/loki/chunks`
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- TSDB index (v13 schema, 24h period)
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- No retention policy configured (logs grow indefinitely)
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- No `limits_config` (no rate limiting, stream limits, or query guards)
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- No caching layer
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- Auth disabled (trusted network)
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**Promtail** on all 16 hosts (`system/monitoring/logs.nix`):
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- Ships systemd journal (JSON) + `/var/log/**/*.log`
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- Labels: `host`, `job` (systemd-journal/varlog), `systemd_unit`
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- Hardcoded to `http://monitoring01.home.2rjus.net:3100`
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**Additional log sources:**
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- `pipe-to-loki` script (manual log submission, `job=pipe-to-loki`)
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- Bootstrap logs from template2 (`job=bootstrap`)
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**Context:** The VictoriaMetrics migration plan (`docs/plans/monitoring-migration-victoriametrics.md`) includes moving Loki to monitoring02 with "same configuration as current". These improvements could be applied either before or after that migration.
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## Improvement Areas
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### 1. Retention Policy
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**Problem:** No retention configured. Logs accumulate until disk fills up.
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**Options:**
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| Approach | Config Location | How It Works |
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|----------|----------------|--------------|
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| **Compactor retention** | `compactor` + `limits_config` | Compactor runs periodic retention sweeps, deleting chunks older than threshold |
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| **Table manager** | `table_manager` | Legacy approach, not recommended for TSDB |
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**Recommendation:** Use compactor-based retention (the modern approach for TSDB/filesystem):
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```nix
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compactor = {
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working_directory = "/var/lib/loki/compactor";
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compaction_interval = "10m";
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retention_enabled = true;
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retention_delete_delay = "2h";
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retention_delete_worker_count = 150;
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};
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limits_config = {
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retention_period = "30d"; # Default retention for all tenants
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};
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```
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30 days aligns with the Prometheus retention and is reasonable for a homelab. Older logs are rarely useful, and anything important can be found in journal archives on the hosts themselves.
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### 2. Storage Backend
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**Decision:** Stay with filesystem storage for now. Garage S3 was considered but ruled out - the current single-node Garage (replication_factor=1) offers no real durability benefit over local disk. S3 storage can be revisited after the NAS migration, when a more robust S3-compatible solution will likely be available.
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### 3. Limits Configuration
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**Problem:** No rate limiting or stream cardinality protection. A misbehaving service could generate excessive logs and overwhelm Loki.
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**Recommendation:** Add basic guardrails:
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```nix
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limits_config = {
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retention_period = "30d";
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ingestion_rate_mb = 10; # MB/s per tenant
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ingestion_burst_size_mb = 20; # Burst allowance
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max_streams_per_user = 10000; # Prevent label explosion
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max_query_series = 500; # Limit query resource usage
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max_query_parallelism = 8;
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};
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```
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These are generous limits that shouldn't affect normal operation but protect against runaway log generators.
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### 4. Promtail Label Improvements
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**Problem:** Label inconsistencies and missing useful metadata:
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- The `varlog` scrape config uses `hostname` while journal uses `host` (different label name)
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- No `tier` or `role` labels, making it hard to filter logs by deployment tier or host function
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**Recommendations:**
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1. **Fix varlog label:** Rename `hostname` to `host` for consistency with journal scrape config
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2. **Add `tier` label:** Static label from `config.homelab.host.tier` (`test`/`prod`) on both scrape configs
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3. **Add `role` label:** Static label from `config.homelab.host.role` on both scrape configs, only when set (10 hosts have no role, so omit to keep labels clean)
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No cardinality impact - `tier` and `role` are 1:1 with `host`, so they add metadata to existing streams without creating new ones.
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This enables queries like:
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- `{tier="prod"} |= "error"` - all errors on prod hosts
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- `{role="dns"}` - all DNS server logs
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- `{tier="test", job="systemd-journal"}` - journal logs from test hosts
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### 5. Journal Priority → Level Label
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**Problem:** Loki 3.6.3 auto-detects a `detected_level` label by parsing log message text for keywords like "INFO", "ERROR", etc. This works for applications that embed level strings in messages (Go apps, Loki itself), but **fails for traditional Unix services** that use the journal `PRIORITY` field without level text in the message.
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Example: NSD logs `"signal received, shutting down..."` with `PRIORITY="4"` (warning), but Loki sets `detected_level="unknown"` because the message has no level keyword. Querying `{detected_level="warn"}` misses these entirely.
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**Recommendation:** Add a Promtail pipeline stage to the journal scrape config that maps the `PRIORITY` field to a `level` label:
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| PRIORITY | level |
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|----------|-------|
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| 0-2 | critical |
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| 3 | error |
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| 4 | warning |
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| 5 | notice |
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| 6 | info |
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| 7 | debug |
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This can be done with a `json` stage to extract PRIORITY, then a `template` + `labels` stage to map and attach it. The journal `PRIORITY` field is always present, so this gives reliable level filtering for all journal logs.
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**Cardinality impact:** Moderate. Adds up to ~6 label values per host+unit combination. In practice most services log at 1-2 levels, so the stream count increase is manageable for 16 hosts. The filtering benefit (e.g., `{level="error"}` to find all errors across the fleet) outweighs the cost.
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This enables queries like:
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- `{level="error"}` - all errors across the fleet
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- `{level=~"critical|error", tier="prod"}` - prod errors and criticals
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- `{level="warning", role="dns"}` - warnings from DNS servers
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### 6. Monitoring CNAME for Promtail Target
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**Problem:** Promtail hardcodes `monitoring01.home.2rjus.net:3100`. The VictoriaMetrics migration plan already addresses this by switching to a `monitoring` CNAME.
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**Recommendation:** This should happen as part of the monitoring02 migration, not independently. If we do Loki improvements before that migration, keep pointing to monitoring01.
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## Priority Ranking
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| # | Improvement | Effort | Impact | Recommendation |
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|---|-------------|--------|--------|----------------|
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| 1 | **Retention policy** | Low | High | Do first - prevents disk exhaustion |
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| 2 | **Limits config** | Low | Medium | Do with retention - minimal additional effort |
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| 3 | **Promtail label fix** | Trivial | Low | Quick fix, do with other label changes |
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| 4 | **Journal priority → level** | Low-medium | Medium | Reliable level filtering across the fleet |
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| 5 | **Monitoring CNAME** | Low | Medium | Part of monitoring02 migration |
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## Implementation Steps
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### Phase 1: Retention + Limits (quick win)
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1. Add `compactor` section to `services/monitoring/loki.nix`
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2. Add `limits_config` with 30-day retention and basic rate limits
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3. Update `system/monitoring/logs.nix`:
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- Fix `hostname` → `host` label in varlog scrape config
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- Add `tier` static label from `config.homelab.host.tier` to both scrape configs
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- Add `role` static label from `config.homelab.host.role` (conditionally, only when set) to both scrape configs
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- Add pipeline stages to journal scrape config: `json` to extract PRIORITY, `template` to map to level name, `labels` to attach as `level`
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4. Deploy to monitoring01, verify compactor runs and old data gets cleaned
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5. Verify `level` label works: `{level="error"}` should return results, and match cases where `detected_level="unknown"`
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### Phase 2 (future): S3 Storage Migration
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Revisit after NAS migration when a proper S3-compatible storage solution is available. At that point, add a new schema period with `object_store = "s3"` - the old filesystem period will continue serving historical data until it ages out past retention.
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## Open Questions
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- [ ] What retention period makes sense? 30 days suggested, but could be 14d or 60d depending on disk/storage budget
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- [ ] Do we want per-stream retention (e.g., keep bootstrap/pipe-to-loki longer)?
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## Notes
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- Loki schema changes require adding a new period entry (not modifying existing ones). The old period continues serving historical data.
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- The compactor is already part of single-process Loki in recent versions - it just needs to be configured.
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- S3 storage deferred until post-NAS migration when a proper solution is available.
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