Metrics and Instrumentation.

What are metrics, and what are the many types of metrics?

Metrics ek prakaar ka numerical data hai jo kisi system, application, ya process ki state, performance, aur behavior ko track karta hai. Jaise:

"Jo data hume batata hai ki system kaisa perform kar raha hai, use Metrics kehte hain."

Metrics = Measurable numbers jo system ki health, performance aur resource usage ko monitor karne ke liye use hote hain.

• CPU usage (%)
• Memory consumption (MB)
• HTTP requests count
• Error rates
• Network traffic, etc.

Time Series Data:-

Data ko time series form mein convert kar ke store karta hai Metrics.
Har time series data ka structure hota hai:

 For example:-

<metric_name>{labels} => value @ timestamp

http_requests_total{method="GET", handler="/home"}  10245  @  1627540200

  metric_name: http_requests_total

  labels: method="GET", handler="/home"

  value: 10245

  timestamp: 1627540200 (Unix time)

yeh format me metric storage hota hai .

metric_name{label="value"} value timestamp

http_requests_total{status="200"} 150 1712800000

Types of Metrics in Prometheus

1.Counter

Sirf increment hota hai (reset ho sakta hai restart pe)

Events count karne ke liye use hota hai. jaise ki "Total HTTP requests"

http_requests_total{method="POST"} 3456

2.Gauge(गेज)

Increase aur decrease dono ho sakta hai

Example: memory_usage_bytes, temperature_celsius

memory_usage_bytes 2048000000

3.Histogram(हिस्टोग्राम)

Values ko buckets (like 0.5s, 1s, 2s...)  mein divide karta hai (distribution ke liye)

Response time, file size, temperature distribution jaise values ke liye useful hai

Example: Request duration

http_request_duration_seconds_bucket{le="1"} 542

http_request_duration_seconds_count 1000

http_request_duration_seconds_sum 780

1000 requests aaye

Total time = 780 seconds

542 requests ≤ 1s ke andar complete ho gaye

4.Summary

Percentile values deta hai, jaise: 50%, 95%, 99% response time

Histogram jaise hi, lekin quantile-based output deta hai

http_request_duration_seconds{quantile="0.95"} 1.3

95% requests 1.3 second ke andar complete hue

Metric Type	Definition	Use in PromQL	Example
Counter	Only increases (can reset to zero, e.g., after app restart)	- To calculate growth rate - To count errors, requests, or events	rate(http_requests_total[5m]) (request rate over 5 min)
Gauge	Can increase or decrease	- To check current values - To measure resource usage	node_memory_Active_bytes (current RAM usage)
Histogram	Splits observations into buckets (e.g., how long requests took to complete in milliseconds)	- To calculate latency distribution - To see how many requests fall into each bucket	rate(http_request_duration_seconds_bucket[5m])
Summary	Similar to Histogram, but directly provides quantiles (percentiles) (e.g., 95th percentile latency)	- To calculate request latency percentiles - Useful when approximate percentiles are needed	http_request_duration_seconds{quantile="0.95"}

What is a Label?

• A label is a key–value pair attached to a metric to differentiate time series.

Example:

http_requests_total{method="GET", status="200"}

method="GET" and status="200" are labels.

The metric name is http_requests_total.

yeh topic add hoge.

1. Label प्रयोग और cardinality implications
2. Best practices in naming metrics
3. Client libraries (Go, Python, Java, etc.) से application instrumentation
4. Custom metrics बनाना और expose करना