Understanding Prometheus Metric Types

const client = require('prom-client');

const httpRequests = new client.Counter({
  name: 'http_requests_total',
  help: 'Total number of HTTP requests',
  labelNames: ['method', 'code']
});

// Increment the counter
httpRequests.inc({ method: 'GET', code: '200' });

const client = require('prom-client');

const requests = new client.Counter({
  name: 'requests_total',
  help: 'Total number of requests by method and status',
  labelNames: ['method', 'status']
});

// Increment with labels
requests.inc({ method: 'POST', status: 'success' });
requests.inc({ method: 'GET', status: 'error' });

const client = require('prom-client');

const gauge = new client.Gauge({
  name: 'nodejs_heap_used_bytes',
  help: 'The number of bytes of the Node.js heap used'
});

gauge.set(1024 * 1024); // Set to 1MB

const client = require('prom-client');

const gauge = new client.Gauge({
  name: 'active_users',
  help: 'Number of active users'
});

gauge.inc(5); // Increment by 5

const client = require('prom-client');

const gauge = new client.Gauge({
  name: 'active_users',
  help: 'Number of active users'
});

gauge.dec(2); // Decrement by 2

groups:
- name: http
  rules:
  - alert: HighRequestLatency
    expr: histogram_quantile(0.95, sum(rate(http_request_duration_seconds_bucket[5m])) by (le))
    for: 10m
    labels:
      severity: page
    annotations:
      summary: "High request latency"

histogram_quantile(0.95, sum(rate(http_request_duration_seconds_bucket[5m])) by (le))

const client = require('prom-client');

const httpRequestDuration = new client.Summary({
  name: 'http_request_duration_seconds',
  help: 'Duration of HTTP requests in seconds',
  percentiles: [0.5, 0.9, 0.99],
});

// Observing a request duration
httpRequestDuration.observe(123.45);

http_requests_total
node_cpu_seconds_total
process_start_time_seconds

up{job="node_exporter", environment="production"}

const httpRequestCounter = new client.Counter({
  name: "http_requests_total",
  help: "Total number of HTTP requests",
  labelNames: ["method", "status"]
});

httpRequestCounter.inc({ method: "GET", status: "200" });

# TYPE http_requests_total counter
http_requests_total{method="get",code="200"} 123
http_requests_total{method="post",code="200"} 45

# TYPE request_duration_seconds histogram
request_duration_seconds_bucket{le="0.05"} 10
request_duration_seconds_bucket{le="0.1"} 25
request_duration_seconds_bucket{le="0.5"} 40
request_duration_seconds_bucket{le="1"} 45
request_duration_seconds_bucket{le="+Inf"} 50
request_duration_seconds_sum 12.3
request_duration_seconds_count 50

const client = new PrometheusClient();

// Counter with custom timestamp
client.registerCounter({
  name: 'http_requests_total',
  help: 'Total number of HTTP requests',
  labelNames: ['method', 'code'],
  values: {
    method: 'GET',
    code: '200'
  },
  timestamp: new Date('2023-10-01T12:00:00Z')
});

// Gauge with custom timestamp
client.registerGauge({
  name: 'memory_usage_bytes',
  help: 'Memory usage in bytes',
  value: 1024 * 1024,
  timestamp: new Date('2023-10-01T12:05:00Z')
});

# HELP http_requests_total Total number of HTTP requests handled by the server
# TYPE http_requests_total counter
http_requests_total{method="GET",code="200"} 1234

http_request_duration_seconds_bucket{le="0.05",method="GET"} 123
http_request_duration_seconds_bucket{le="0.1",method="GET"} 234
http_request_duration_seconds_bucket{le="0.5",method="GET"} 345
http_request_duration_seconds_count{method="GET"} 456
http_request_duration_seconds_sum{method="GET"} 123.45

http_request_duration_seconds{quantile="0.5",method="GET"} 0.03
http_request_duration_seconds{quantile="0.9",method="GET"} 0.07
http_request_duration_seconds{quantile="0.99",method="GET"} 0.12
http_request_duration_seconds_count{method="GET"} 456
http_request_duration_seconds_sum{method="GET"} 123.45

// Simulate counter reset using a gauge to track the last value
const client = require('prom-client');

// Create a counter
const counter = new client.Counter({
  name: 'requests_total',
  help: 'Total number of requests',
});

// Simulate reset logic using a gauge
const lastValue = new client.Gauge({
  name: 'last_request_value',
  help: 'Last known counter value before reset'
});

// Function to simulate a reset
function simulateReset() {
  const currentValue = counter.get();
  lastValue.set(currentValue);
  counter.reset(); // Reset the counter to zero
}

// Example usage:
counter.inc();
simulateReset();

// The gauge now holds the previous value for reference
console.log('Last counter value:', lastValue.get());