Prometheus exporter in Nginx - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a Prometheus exporter?

A Prometheus exporter is a tool that collects metrics from a system or application and exposes them in a format Prometheus can read.

beginner

Why do we need a Prometheus exporter for Nginx?

Nginx does not expose metrics in Prometheus format by default, so an exporter collects Nginx stats and converts them for Prometheus to scrape.

intermediate

Which Nginx module is commonly used to expose metrics for Prometheus?

The 'nginx-prometheus-exporter' or a sidecar exporter is commonly used to expose Nginx metrics in Prometheus format.

beginner

How does Prometheus get metrics from an exporter?

Prometheus periodically sends HTTP requests to the exporter's metrics endpoint to collect the current metrics data.

intermediate

What kind of metrics can the Nginx Prometheus exporter provide?

It can provide metrics like request counts, response statuses, connection states, and request durations.

What is the main role of a Prometheus exporter?

A To collect and expose metrics in Prometheus format

B To store metrics data permanently

C To visualize metrics in dashboards

D To send alerts based on metrics

Exporters collect metrics from applications and expose them so Prometheus can scrape them.

Which protocol does Prometheus use to scrape metrics from an exporter?

A FTP

B HTTP

C SSH

D SMTP

Prometheus scrapes metrics by sending HTTP requests to the exporter endpoint.

Why can't Prometheus directly scrape Nginx metrics without an exporter?

A Nginx metrics are encrypted

B Prometheus only works with databases

C Nginx blocks Prometheus IPs

D Nginx does not expose metrics in Prometheus format by default

Nginx needs an exporter to convert its stats into Prometheus format.

Which of these is NOT a typical metric provided by the Nginx Prometheus exporter?

A Request count

B Connection states

C CPU temperature

D Response status codes

CPU temperature is not provided by the Nginx exporter; it focuses on web server metrics.

How often does Prometheus scrape metrics from exporters by default?

A Every 15 seconds

B Every 1 second

C Every 1 hour

D Only once at startup

Prometheus usually scrapes metrics every 15 seconds by default.

Explain how a Prometheus exporter works with Nginx to provide monitoring data.

Think about how data flows from Nginx to Prometheus.

Describe the steps to set up a Prometheus exporter for Nginx.

Focus on installation, configuration, and scraping.

Practice

1. What is the main purpose of the stub_status module in nginx when used with Prometheus?

easy

A. To expose basic nginx metrics like active connections and requests

B. To serve static web pages faster

C. To block unauthorized IP addresses

D. To cache dynamic content for faster delivery

Solution

1. Step 1: Understand stub_status role

   The stub_status module provides a simple status page with metrics like active connections, accepts, handled, and requests.

2. Step 2: Connect stub_status to Prometheus

   Prometheus scrapes these metrics from the URL where stub_status is enabled to monitor nginx performance.

3. Final Answer:

   To expose basic nginx metrics like active connections and requests -> Option A

4. Quick Check:

   stub_status exposes metrics = C [OK]

Hint: stub_status shows nginx metrics, not content or blocking [OK]

Common Mistakes:

• Thinking stub_status caches content
• Confusing stub_status with IP blocking
• Assuming stub_status serves web pages

2. Which nginx configuration snippet correctly enables stub_status at the URL /metrics and restricts access to 127.0.0.1?

easy

A. location /metrics { stub_status on; allow all; }

B. location /metrics { stub_status; }

C. location /metrics { stub_status; allow 127.0.0.1; deny all; }

D. location /metrics { stub_status on; }

Solution

1. Step 1: Check stub_status syntax

   The correct directive is stub_status; without 'on'. It must be inside a location block.

2. Step 2: Verify access control

   To protect metrics, use allow 127.0.0.1; and deny all; inside the location.

3. Final Answer:

   location /metrics { stub_status; allow 127.0.0.1; deny all; } -> Option C

4. Quick Check:

   stub_status syntax + IP allow/deny = A [OK]

Hint: stub_status has no 'on'; protect with allow/deny [OK]

Common Mistakes:

• Using 'stub_status on;' which is invalid
• Not adding IP allow/deny rules
• Missing semicolon after stub_status

3. Given this nginx stub_status output scraped by Prometheus:

Active connections: 5
server accepts handled requests
 100 100 200
Reading: 1 Writing: 2 Waiting: 2

What is the value of 'Active connections' metric?

medium

A. 1

B. 100

C. 200

D. 5

Solution

1. Step 1: Identify Active connections line

   The first line shows 'Active connections: 5', so the active connections count is 5.

2. Step 2: Differentiate other numbers

   Numbers 100 and 200 relate to accepts, handled, and requests, not active connections.

3. Final Answer:

   5 -> Option D

4. Quick Check:

   Active connections = 5 [OK]

Hint: Active connections is the first number after label [OK]

Common Mistakes:

• Confusing accepts or requests with active connections
• Picking the largest number instead of the labeled one
• Ignoring the label and choosing Reading/Writing values

4. You configured nginx with stub_status at /metrics but Prometheus shows 'connection refused'. What is the most likely cause?

medium

A. nginx is not running or listening on the expected port

B. The stub_status directive is misspelled as stubstatus

C. Prometheus URL is missing the trailing slash

D. The location /metrics block is missing a root directive

Solution

1. Step 1: Understand 'connection refused' meaning

   This error means Prometheus cannot connect to nginx, likely because nginx is down or not listening on the port.

2. Step 2: Check other options

   Misspelling stub_status causes config errors but not connection refused. Missing slash or root directive won't cause connection refused.

3. Final Answer:

   nginx is not running or listening on the expected port -> Option A

4. Quick Check:

   Connection refused = nginx down or port closed [OK]

Hint: Connection refused means no server listening on port [OK]

Common Mistakes:

• Assuming URL slash causes connection refused
• Thinking config typos cause connection refused
• Believing root directive is required for stub_status

5. You want to expose nginx metrics at /metrics only to Prometheus server IP 10.0.0.5. Which configuration snippet correctly achieves this?

hard

A. location /metrics { stub_status on; allow 10.0.0.5; deny all; }

B. location /metrics { stub_status; allow 10.0.0.5; deny all; }

C. location /metrics { stub_status; allow all; deny 10.0.0.5; }

D. location /metrics { stub_status; deny all; allow 10.0.0.5; }

Solution

1. Step 1: Use correct stub_status syntax

   The directive is stub_status; without 'on'. It must be inside the location block.

2. Step 2: Apply IP allow/deny rules correctly

   To allow only 10.0.0.5, use allow 10.0.0.5; then deny all;. Order matters: allow first, then deny.

3. Final Answer:

   location /metrics { stub_status; allow 10.0.0.5; deny all; } -> Option B

4. Quick Check:

   Correct stub_status + allow IP then deny all = B [OK]

Hint: Allow IP first, then deny all; stub_status has no 'on' [OK]

Common Mistakes:

• Using 'stub_status on;' which is invalid
• Reversing allow and deny order
• Allowing all and denying the IP instead