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incus-contrib/notes/observability-guide.md

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Observability Stack — Prometheus, Grafana, Loki on Incus

A lightweight observability stack deployed as Incus containers on the lab cluster. Provides metric collection (Prometheus), dashboards (Grafana), and log aggregation (Loki) for Incus nodes, HAProxy load balancers, and host-level resources.

The stack runs entirely on OVN and is managed by the deploy-observability script. All containers use the monitoring-allow ACL to permit scrape traffic on the shared network.

Architecture

flowchart TD
    lan(["LAN 192.168.103.0/24"])

    subgraph fwd["OVN Forward · 192.168.103.201"]
        fwd_grafana[":3000 → Grafana"]
        fwd_prom[":9090 → Prometheus"]
    end

    subgraph mon["monitoring · 10.10.10.70 · oc-node-02"]
        prometheus["Prometheus :9090"]
        grafana["Grafana :3000"]
        loki["Loki :3100<br/>gRPC :9096"]
        promtail["Promtail"]
    end

    subgraph targets["Scrape Targets"]
        incus["Incus nodes :8443<br/>.140 · .141 · .142"]
        haproxy["HAProxy :8404<br/>.50 · .51"]
        ne["node-exporters :9100<br/>.71 · .72 · .73"]
    end

    lan --> fwd
    fwd --> mon
    prometheus -->|"client cert"| incus
    prometheus --> haproxy
    prometheus --> ne

    classDef external fill:#f5f5f5,color:#333,stroke:#999
    classDef network fill:#0072B2,color:#fff,stroke:#005a8e
    classDef mgmt fill:#CC79A7,color:#fff,stroke:#a36088
    classDef instance fill:#56B4E9,color:#fff,stroke:#3a8fbf
    classDef node fill:#009E73,color:#fff,stroke:#007a5e

    class lan external
    class fwd_grafana,fwd_prom network
    class prometheus,grafana,loki,promtail mgmt
    class incus,haproxy,ne instance

    style fwd fill:#e0eef8,stroke:#0072B2
    style mon fill:#f5e6f0,stroke:#CC79A7
    style targets fill:#e0f2fe,stroke:#56B4E9

Components

Prometheus 2.54

Metric collection engine. Scrapes all targets at a 15-second interval.

  • Stores metrics locally in the monitoring container
  • Client certificate authentication for Incus /1.0/metrics endpoints (uses cluster client cert + key)
  • Plain HTTP scrape for HAProxy stats (:8404/metrics) and node-exporters (:9100/metrics)

Grafana 12.4

Dashboard and visualization frontend.

  • Default credentials: admin / admin
  • Pre-provisioned datasources for Prometheus and Loki
  • Three dashboards deployed automatically (see Dashboards section)
  • Accessible from LAN via OVN network forward

Loki 3.6

Log aggregation backend.

  • HTTP API on port 3100
  • gRPC on port 9096 (not the default 9095 -- avoids conflict with Promtail's own metrics port)
  • 7-day retention policy
  • Receives logs from Promtail running in the same container

Promtail 3.6

Log shipping agent, co-located with Loki in the monitoring container.

  • Pushes logs to Loki via gRPC on localhost:9096
  • Scrapes container logs and system journal

node_exporter

Host-level metrics via privileged Alpine containers.

  • One container per cluster node, pinned with --target placement
  • Privileged containers with host filesystem bind-mounts:
    • /proc (host) -> /host/proc (read-only)
    • /sys (host) -> /host/sys (read-only)
    • / (host) -> /host/rootfs (read-only)
  • Exposes standard node_exporter metrics on :9100
  • Uses monitoring-allow ACL for network access

Access

Service URL Credentials
Grafana http://192.168.103.201:3000 admin / admin
Prometheus http://192.168.103.201:9090 None (open)

Both services are accessible from the LAN through an OVN network forward on IP 192.168.103.201. The forward maps external ports directly to the monitoring container's internal ports (no translation).

Prometheus and Loki are not exposed externally by default. They are accessible only from within the OVN network or through the Grafana datasource proxy.

Dashboards

Three dashboards are provisioned automatically during deployment.

Incus Cluster Overview

Visualizes metrics scraped from the Incus /1.0/metrics endpoint on each cluster node.

  • Instance CPU usage (per-instance, per-node)
  • Memory usage and allocation
  • Network I/O (bytes in/out per interface)
  • Disk I/O (reads/writes, latency)
  • Instance count and state

HAProxy Traffic

Visualizes metrics from the HAProxy stats endpoint (:8404/metrics).

  • Request rate (frontend and backend)
  • Backend health status (UP/DOWN per server)
  • Active sessions and session rate
  • Traffic volume (bytes in/out)
  • HTTP response codes (2xx, 4xx, 5xx)
  • Connection errors and retries

Host Resources

Visualizes metrics from node_exporter on each cluster node.

  • CPU utilization (%)
  • Memory utilization (%)
  • Disk usage and I/O
  • Network throughput per interface
  • System load averages
  • Filesystem free space

ACL Configuration

Aether automatically creates per-instance ACLs with default-deny rules for all containers on shared OVN networks. The observability stack needs careful ACL configuration to allow scrape traffic.

How Aether ACLs work

When Aether deploys a container, it creates ACLs with reject rules:

Direction Priority Action Effect
Egress 111 reject Blocks all outbound by default
Ingress 100 reject Blocks all inbound by default

These are OVN ACL rules enforced at the logical switch port level.

monitoring-allow ACL

The observability containers use a monitoring-allow ACL with default.*.action=allow set on all directions. This creates allow rules at priority 111 which matches or exceeds the Aether reject rules, effectively overriding the default-deny policy.

All observability containers (monitoring, node-exp-01/02/03) have this ACL applied.

HAProxy scrape access

HAProxy containers are managed by Aether and have their own ACLs with default-deny. For Prometheus to scrape HAProxy metrics on :8404, the HAProxy Aether ACLs need explicit ingress rules allowing TCP traffic from the monitoring container (10.10.10.70) to port 8404.

Without this, Prometheus targets for HAProxy will show as DOWN.

NIC state after ACL changes

Changing security.acls on a container NIC can cause the NIC to go down. After modifying ACLs, you may need to bring the NIC back up manually or restart the container.

Resource Budget

Container Image RAM Disk Placement
monitoring Debian/12 2 GiB 20 GiB oc-node-02
node-exp-01 Alpine 128 MiB — oc-node-01
node-exp-02 Alpine 128 MiB — oc-node-02
node-exp-03 Alpine 128 MiB — oc-node-03

Totals:

  • RAM: ~2.4 GiB (2 GiB + 3 x 128 MiB)
  • Disk: 20 GiB (only the monitoring container needs significant storage)
  • OVN forward IPs: 1 (192.168.103.201)
  • OVN network IPs: 4 (10.10.10.70-73)

Management

The deploy-observability script handles the full lifecycle.

Deploy the stack

incusos/deploy-observability --deploy

Creates the monitoring container and all node-exporter containers, installs and configures Prometheus, Grafana, Loki, and Promtail, provisions dashboards, sets up the OVN network forward, and configures ACLs.

Check status

incusos/deploy-observability --status

Shows the state of all containers, scrape target health, Grafana accessibility, and OVN forward configuration.

Clean up

incusos/deploy-observability --cleanup

Removes all observability containers, the OVN network forward, and associated ACLs. Does not affect monitored targets (Incus nodes, HAProxy).

Health check

incusos/deploy-observability --doctor

Verifies prerequisites, checks container health, validates Prometheus targets are UP, confirms Grafana datasources are working, and reports any ACL issues.

Troubleshooting

Targets show as DOWN in Prometheus

  1. Check ACL rules on the target containers. Aether's default-deny ACLs block all ingress including Prometheus scrapes.
  2. Verify the NIC is up. Changing security.acls can bring the NIC down. Check with incus exec <container> -- ip link and bring it up if needed.
  3. For Incus node targets: verify the client certificate and key are correctly placed in the Prometheus config directory and that the cert is trusted by the cluster.

Grafana can't reach Prometheus

Check that Prometheus is running and listening on localhost:9090 from inside the monitoring container:

incus exec monitoring -- curl -s http://localhost:9090/-/healthy

If Prometheus is not running, check its service status:

incus exec monitoring -- systemctl status prometheus

No node metrics

  1. Verify the node-exporter containers are running and privileged: 
    incus list node-exp
  2. Check that host filesystem mounts are in place: 
    incus exec node-exp-01 -- ls /host/proc/stat
  3. Verify node_exporter is listening: 
    incus exec node-exp-01 -- wget -qO- http://localhost:9100/metrics | head

HAProxy metrics show as invalid or empty

HAProxy needs the prometheus-exporter service enabled in its stats configuration. The stats section in haproxy.cfg must include:

frontend stats
    bind *:8404
    http-request use-service prometheus-exporter if { path /metrics }
    stats enable
    stats uri /stats

Without the use-service prometheus-exporter directive, the /metrics path returns HTML stats instead of Prometheus-format metrics.

Loki not receiving logs

Verify Promtail can reach Loki on the gRPC port:

incus exec monitoring -- curl -s http://localhost:3100/ready

Note that Loki uses gRPC port 9096 in this deployment (not the default 9095) to avoid conflicts with Promtail's metrics port.