Applications cannot always expose Prometheus metrics natively. Exporters act as translators: they query third-party systems, databases, or operating systems and expose metrics in the standard Prometheus text exposition format.
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The Prometheus Text Exposition Format
When you run curl http://localhost:9100/metrics, you see the OpenMetrics standard format:
text
# HELP node_cpu_seconds_total Seconds the CPUs spent in each mode.
# TYPE node_cpu_seconds_total counter
node_cpu_seconds_total{cpu="0",mode="idle"} 438291.12
node_cpu_seconds_total{cpu="0",mode="system"} 1284.90
node_cpu_seconds_total{cpu="0",mode="user"} 8421.43
# HELP node_memory_MemAvailable_bytes Memory information field MemAvailable_bytes.
# TYPE node_memory_MemAvailable_bytes gauge
node_memory_MemAvailable_bytes 1.4827163648e+10
Each metric contains:
# HELP: Human-readable documentation.# TYPE: Metric type (counter,gauge,histogram,summary).- Metric Name + Key/Value Labels.
- Float64 Value.
1. Node Exporter: Deep Linux Host Metrics
Node Exporter gathers deep operating system hardware metrics from /proc and /sys.
Key Metric Families:
node_cpu_seconds_total: CPU breakdown by core and mode (idle, user, system, iowait, steal).node_memory_*: Memory utilization, buffers, cached, available RAM.node_disk_*: Disk read/write operations, bytes transferred, disk queue time (I/O saturation).node_network_*: Inbound/outbound bytes, dropped packets, interface errors.node_filesystem_*: Free disk space and total inodes.
2. cAdvisor: Container Metrics
cAdvisor (Container Advisor) by Google auto-discovers all running Docker containers and measures CPU, memory, filesystem, and network usage per container.
Key Metric Families:
container_memory_working_set_bytes: Actual memory used (matches the Linux OOM Killer threshold).container_cpu_usage_seconds_total: Total CPU consumed by container.container_cpu_cfs_throttled_periods_total: Count of times container hit its CPU limit and was throttled!
Complete Multi-Service Stack Configuration
Here is the complete docker-compose.yml to run Prometheus, Node Exporter, and cAdvisor:
yaml
version: "3.8"
services:
prometheus:
image: prom/prometheus:v2.52.0
container_name: prometheus
volumes:
- ./prometheus.yml:/etc/prometheus/prometheus.yml:ro
ports:
- "9090:9090"
restart: unless-stopped
node-exporter:
image: prom/node-exporter:v1.8.1
container_name: node-exporter
pid: host
restart: unless-stopped
volumes:
- /proc:/host/proc:ro
- /sys:/host/sys:ro
- /:/rootfs:ro
command:
- "--path.procfs=/host/proc"
- "--path.sysfs=/host/sys"
- "--path.rootfs=/rootfs"
- "--collector.filesystem.mount-points-exclude=^/(sys|proc|dev|host|etc)($$|/)"
ports:
- "9100:9100"
cadvisor:
image: gcr.io/cadvisor/cadvisor:v0.49.1
container_name: cadvisor
restart: unless-stopped
privileged: true
volumes:
- /:/rootfs:ro
- /var/run:/var/run:ro
- /sys:/sys:ro
- /var/lib/docker/:/var/lib/docker:ro
- /dev/disk/:/dev/disk:ro
ports:
- "8080:8080"
Start the containers:
bash
docker compose up -d