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World O2: Counters

Exporters: node and blackbox

You will learn: how exporters translate a machine or a web page into numbers Prometheus can scrape.

Checked with Prometheus 3 on 1 Nov 2026

The problem

The stove cannot speak Prometheus. How do you get its temperature onto a screen?

Watch

Tap the line that explains free disk space.

0 of 1 found

An exporter: A translator: it reads numbers from something (a machine, a database) and shows them at /metrics. translates. Node exporter reads a machine: CPU, memory, disk, load. These lines are real.

Try it

What share of memory is free on each machine? Divide available by total.

Add / node_memory_MemTotal_bytes, then Run.

Metrics in this data (tap to add):

Time 0 is when the data starts. The query looks back from the eval time.

Watch

bash
curl -s 'localhost:9115/probe?target=http://prometheus:9090/-/ready&module=http_2xx' | grep -E 'probe_success|probe_http_status_code'
# HELP probe_http_status_code Response HTTP status code
# TYPE probe_http_status_code gauge
probe_http_status_code 200
# HELP probe_success Displays whether or not the probe was a success
# TYPE probe_success gauge
probe_success 1

Blackbox exporter knocks on a page from outside, like a customer. probe_success 1 means the door opened. This output is real.

Try it

Which shop page fails its knock at 12m?

Show only failed probes: type probe_success == 0 and Run.

Metrics in this data (tap to add):

Time 0 is when the data starts. The query looks back from the eval time.

Predict

At 12m, blackbox’s own up is 1. But probe_success for the home page is 0. Why?

Try it

Inside view or outside view? Sort each check.

Drag a card into a box. Or tap the card, then tap the box.

      You did it!

      You can now explain exporters and read node and blackbox numbers.

      Go deeper (optional)

      Many exporters exist: databases, Redis, message queues. Your own app can also show /metrics with a client library. Real rep: add blackbox to your kedai-watch stack. Add this service to compose.yaml, and this job to prometheus.yml.

        blackbox-exporter:
    image: quay.io/prometheus/blackbox-exporter:v0.29.1
    ports:
      - "9115:9115"
        - job_name: blackbox
    metrics_path: /probe
    params:
      module: [http_2xx]
    static_configs:
      - targets: ["http://prometheus:9090/-/ready"]
    relabel_configs:
      - source_labels: [__address__]
        target_label: __param_target
      - source_labels: [__param_target]
        target_label: instance
      - target_label: __address__
        replacement: blackbox-exporter:9115

      Real mission

      2. docker compose up -d
      3. curl -s 'localhost:9115/probe?target=http://prometheus:9090/-/ready&module=http_2xx' | grep -E 'probe_success|probe_http_status_code'
      5. docker compose down

      0 of 5 steps done · Your ticks are saved.