Prometheus for metrics collection in Kubernetes - Step-by-Step Execution

Process Flow - Prometheus for metrics collection

Start Prometheus

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Scrape Targets Configured

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Send HTTP Requests to Targets

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Targets Respond with Metrics

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Prometheus Stores Metrics

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Query Metrics via PromQL

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Visualize or Alert Based on Data

Prometheus starts, scrapes configured targets by HTTP, stores metrics, and allows querying or alerting.

Execution Sample

Kubernetes

scrape_configs:
  - job_name: 'example'
    static_configs:
      - targets: ['localhost:9090']

This config tells Prometheus to scrape metrics from localhost on port 9090 under job 'example'.

Process Table

Step	Action	Target	Request Sent	Response Received	Metrics Stored
1	Start Prometheus	-	No	No	No
2	Load scrape configs	localhost:9090	No	No	No
3	Send HTTP request	localhost:9090	Yes	No	No
4	Receive metrics response	localhost:9090	Yes	Yes	No
5	Store metrics data	localhost:9090	Yes	Yes	Yes
6	Wait for next scrape interval	-	No	No	Yes

💡 Prometheus continuously scrapes targets at configured intervals; this trace shows one scrape cycle.

Status Tracker

Variable	Start	After Step 2	After Step 4	After Step 5	Final
Prometheus State	Stopped	Running	Running	Running	Running
Scrape Targets	None	localhost:9090	localhost:9090	localhost:9090	localhost:9090
Metrics Data	Empty	Empty	Received	Stored	Stored

Key Moments - 3 Insights

Why does Prometheus send HTTP requests to targets?

Prometheus scrapes metrics by sending HTTP requests to targets as shown in step 3 of the execution_table to collect their current metrics.

What happens if a target does not respond with metrics?

If no response is received (step 4), Prometheus cannot store metrics for that scrape cycle, so metrics data remains unchanged as shown in the execution_table.

Does Prometheus store metrics permanently after one scrape?

Prometheus stores metrics after each successful scrape (step 5), but it continuously updates data over time, not permanently after one scrape.

Visual Quiz - 3 Questions

Look at the execution_table, at which step does Prometheus receive metrics from the target?

A Step 2

B Step 3

C Step 4

D Step 5

💡 Hint

Check the 'Response Received' column in the execution_table to find when metrics arrive.

According to variable_tracker, what is the state of 'Metrics Data' after step 5?

A Stored

B Empty

C Received

D None

💡 Hint

Look at the 'Metrics Data' row under 'After Step 5' in variable_tracker.

If the target at localhost:9090 did not respond, which step in execution_table would show 'No' under 'Response Received'?

A Step 3

B Step 4

C Step 5

D Step 6

💡 Hint

The 'Response Received' column shows 'Yes' or 'No' at each step; check step 4.

Concept Snapshot

Prometheus scrapes metrics by sending HTTP requests to configured targets.
Targets expose metrics on HTTP endpoints.
Prometheus stores scraped metrics for querying and alerting.
Scrape configs define which targets and how often to scrape.
PromQL queries allow extracting insights from stored metrics.

Full Transcript

Prometheus is a tool that collects metrics by regularly sending HTTP requests to configured targets. It starts by loading its scrape configuration, which lists the targets to monitor. Then it sends HTTP requests to these targets to get their current metrics. When targets respond, Prometheus stores the metrics data. This process repeats continuously at set intervals. If a target does not respond, Prometheus skips storing new data for that cycle. The stored metrics can be queried or used for alerts. This visual trace shows one full scrape cycle from start to storing metrics.