create a working example of vector internal metrics monitoring

Signed-off-by: Jérémie Drouet <[email protected]>

internal-metrics-monitoring/README.md

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+# Vector internal metrics monitoring
+
+This demo shows how to monitor Vector's [internal metrics](https://vector.dev/docs/reference/configuration/sources/internal_metrics/) using [Prometheus](https://prometheus.io/).
+
+## How to start it
+
+To start it, you first need to clone this repository, go into the `internal-metrics-monitoring` folder and run `docker-compose up`.
+

internal-metrics-monitoring/docker-compose.yml

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+version: '3.9'
+
+services:
+  vector:
+    image: timberio/vector:latest-alpine
+    environment:
+      - LOG=info
+    networks:
+      - backend
+    volumes:
+      - ./vector:/etc/vector:ro
+
+  prometheus:
+    image: bitnami/prometheus:latest
+    networks:
+      - backend
+    ports:
+      - 9090:9090
+    volumes:
+      - ./prometheus/prometheus.yml:/opt/bitnami/prometheus/conf/prometheus.yml:ro
+
+networks:
+  backend: {}
+

internal-metrics-monitoring/prometheus/prometheus.yml

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+# my global config
+global:
+  scrape_interval:     10s # Set the scrape interval to every 15 seconds. Default is every 1 minute.
+  evaluation_interval: 15s # Evaluate rules every 15 seconds. The default is every 1 minute.
+  # scrape_timeout is set to the global default (10s).
+
+  # Attach these labels to any time series or alerts when communicating with
+  # external systems (federation, remote storage, Alertmanager).
+  external_labels:
+      monitor: 'vector-monitor'
+
+# Load rules once and periodically evaluate them according to the global 'evaluation_interval'.
+rule_files:
+  # - "first.rules"
+  # - "second.rules"
+
+# A scrape configuration containing exactly one endpoint to scrape:
+# Here it's Prometheus itself.
+scrape_configs:
+  # The job name is added as a label `job=<job_name>` to any timeseries scraped from this config.
+  - job_name: 'activity'
+
+    # metrics_path defaults to '/metrics'
+    # scheme defaults to 'http'.
+
+    static_configs:
+      - targets: ['vector:9090']

internal-metrics-monitoring/vector/vector.toml

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+[sources.random]
+type = "demo_logs"
+format = "json"
+
+[sinks.blackhole]
+type = "blackhole"
+inputs = ["random"]
+
+[sources.internal_metrics]
+type = "internal_metrics"
+
+[sinks.prometheus]
+type = "prometheus_exporter"
+inputs = ["internal_metrics"]
+address = "0.0.0.0:9090"