Prometheus for Docker monitoring - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to start a Prometheus container with the official image.

Docker

docker run -d --name prometheus [1] prom/prometheus

Drag options to blanks, or click blank then click option'

A-p 9090:9090

B-p 8080:8080

C-p 3000:3000

D-p 80:80

Attempts:

3 left

💡 Hint

Common Mistakes

Mapping the wrong port like 8080 or 3000 which are not Prometheus default ports.

Forgetting to expose any port so you can't access Prometheus UI.

The Prometheus server listens on port 9090 by default, so we map port 9090 from the container to the host.

2fill in blank

medium

Complete the command to mount a local Prometheus configuration file into the container.

Docker

docker run -d --name prometheus -p 9090:9090 -v [1]:/etc/prometheus/prometheus.yml prom/prometheus

Drag options to blanks, or click blank then click option'

A/etc/prometheus/prometheus.yml

B/var/lib/prometheus/data

C/home/user/prometheus.yml

D/home/user/data

Attempts:

3 left

💡 Hint

Common Mistakes

Mounting a directory instead of the config file.

Using the wrong local path that does not exist.

You need to mount your local Prometheus config file (e.g., /home/user/prometheus.yml) to the container's expected config path.

3fill in blank

hard

Fix the error in the Prometheus scrape config to monitor Docker metrics.

Docker

scrape_configs:
  - job_name: 'docker'
    static_configs:
      - targets: ['[1]']

Drag options to blanks, or click blank then click option'

Alocalhost:9100

Blocalhost:2375

Clocalhost:8080

Dlocalhost:9090

Attempts:

3 left

💡 Hint

Common Mistakes

Using the Prometheus port 9090 as a target.

Using node exporter port 9100 which is unrelated to Docker metrics.

Docker metrics are exposed on the Docker daemon API port 2375 (if enabled). Prometheus scrapes this target.

4fill in blank

hard

Fill both blanks to configure Prometheus to scrape metrics from Docker and node exporter.

Docker

scrape_configs:
  - job_name: 'docker'
    static_configs:
      - targets: ['[1]']
  - job_name: 'node'
    static_configs:
      - targets: ['[2]']

Drag options to blanks, or click blank then click option'

Alocalhost:2375

Blocalhost:9100

Clocalhost:9090

Dlocalhost:8080

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing up ports for Docker and node exporter.

Using Prometheus port 9090 as a scrape target.

Docker metrics come from port 2375, node exporter metrics come from port 9100.

5fill in blank

hard

Fill all three blanks to create a Docker Compose service for Prometheus with port mapping and config volume.

Docker

services:
  prometheus:
    image: prom/prometheus
    ports:
      - '[1]:9090'
    volumes:
      - '[2]:/etc/prometheus/prometheus.yml'
    command:
      - '--config.file=[3]'

Drag options to blanks, or click blank then click option'

A9090

B/home/user/prometheus.yml

C/etc/prometheus/prometheus.yml

Dprometheus.yml

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong port numbers or paths.

Not specifying the config file path in the command.

Map host port 9090 to container 9090, mount local config file, and tell Prometheus where the config file is inside the container.

Practice

1. What is the main role of Prometheus when monitoring Docker containers?

easy

A. To run Docker containers automatically

B. To collect and store metrics from Docker containers

C. To build Docker images from Dockerfiles

D. To replace Docker Engine for container management

Solution

1. Step 1: Understand Prometheus purpose

   Prometheus is designed to collect and store metrics data from various sources, including Docker containers.

2. Step 2: Differentiate from other Docker tools

   Prometheus does not run containers, build images, or replace Docker Engine; it focuses on monitoring.

3. Final Answer:

   To collect and store metrics from Docker containers -> Option B

4. Quick Check:

   Prometheus = Metrics collection [OK]

Hint: Remember: Prometheus collects data, not runs containers [OK]

Common Mistakes:

• Confusing Prometheus with Docker Engine
• Thinking Prometheus builds images
• Assuming Prometheus runs containers

2. Which Docker command correctly starts cAdvisor to provide metrics for Prometheus?

easy

A. docker run --name cadvisor -p 8080:8080 gcr.io/cadvisor/cadvisor:latest

B. docker run --name cadvisor -p 8080:8080 google/cadvisor:latest

C. docker run --name cadvisor -p 9090:9090 prom/cadvisor:latest

D. docker run --name cadvisor -p 9090:8080 google/cadvisor:stable

Solution

1. Step 1: Identify correct cAdvisor image and port

   The official cAdvisor image is hosted at gcr.io/cadvisor/cadvisor:latest and listens on port 8080.

2. Step 2: Check port mapping and image name

   docker run --name cadvisor -p 8080:8080 gcr.io/cadvisor/cadvisor:latest correctly maps port 8080:8080 and uses the official image name.

3. Final Answer:

   docker run --name cadvisor -p 8080:8080 gcr.io/cadvisor/cadvisor:latest -> Option A

4. Quick Check:

   cAdvisor image and port = docker run --name cadvisor -p 8080:8080 gcr.io/cadvisor/cadvisor:latest [OK]

Hint: Official cAdvisor image is gcr.io/cadvisor/cadvisor:latest [OK]

Common Mistakes:

• Using wrong image repository
• Mapping wrong ports
• Using outdated or incorrect image tags

3. Given this Prometheus scrape config snippet for Docker monitoring:

scrape_configs:
  - job_name: 'cadvisor'
    static_configs:
      - targets: ['localhost:8080']

What will Prometheus do when started with this config?

medium

A. Fail to start due to invalid config syntax

B. Scrape metrics from Docker Engine API on port 8080

C. Scrape metrics from all Docker containers directly

D. Scrape metrics from cAdvisor running on localhost port 8080

Solution

1. Step 1: Analyze scrape_configs job_name and targets

   The job 'cadvisor' targets 'localhost:8080', which is the default cAdvisor port.

2. Step 2: Understand Prometheus scraping behavior

   Prometheus will scrape metrics from the specified target, not Docker Engine API or all containers directly.

3. Final Answer:

   Scrape metrics from cAdvisor running on localhost port 8080 -> Option D

4. Quick Check:

   Prometheus scrapes targets listed = Scrape metrics from cAdvisor running on localhost port 8080 [OK]

Hint: Targets in scrape_configs define where Prometheus scrapes [OK]

Common Mistakes:

• Confusing cAdvisor with Docker Engine API
• Assuming Prometheus scrapes containers directly
• Thinking config syntax is invalid

4. You started Prometheus and cAdvisor with Docker Compose, but Prometheus shows no metrics from cAdvisor. What is the likely cause?

medium

A. Prometheus cannot scrape metrics from port 9090

B. Prometheus config has wrong job_name

C. cAdvisor container is not exposing port 8080 to Prometheus

D. Docker Compose file is missing image tags

Solution

1. Step 1: Check port exposure between cAdvisor and Prometheus

   If cAdvisor does not expose port 8080 or network is misconfigured, Prometheus cannot scrape metrics.

2. Step 2: Verify other options

   Wrong job_name or missing image tags usually cause errors but not silent no metrics; port 9090 is Prometheus default, not cAdvisor.

3. Final Answer:

   cAdvisor container is not exposing port 8080 to Prometheus -> Option C

4. Quick Check:

   Port exposure needed for scraping = cAdvisor container is not exposing port 8080 to Prometheus [OK]

Hint: Check port mapping between containers first [OK]

Common Mistakes:

• Ignoring port exposure issues
• Assuming job_name mismatch causes no metrics
• Confusing Prometheus and cAdvisor ports

5. You want to monitor multiple Docker hosts with Prometheus and cAdvisor. Which setup is best?

hard

A. Run cAdvisor on each host exposing metrics, configure Prometheus to scrape all hosts

B. Run one cAdvisor container on a central host to monitor all hosts

C. Run Prometheus on each host and aggregate metrics manually

D. Use Docker Compose to run a single cAdvisor and Prometheus on one host only

Solution

1. Step 1: Understand cAdvisor scope

   cAdvisor monitors containers on the host it runs on; to monitor multiple hosts, run cAdvisor on each host.

2. Step 2: Configure Prometheus for multi-host scraping

   Prometheus can scrape metrics from multiple cAdvisor instances by listing all hosts in its config.

3. Step 3: Evaluate other options

   Central cAdvisor cannot monitor other hosts; running Prometheus on each host complicates aggregation; single host setup misses other hosts.

4. Final Answer:

   Run cAdvisor on each host exposing metrics, configure Prometheus to scrape all hosts -> Option A

5. Quick Check:

   One cAdvisor per host + Prometheus scrape all = Run cAdvisor on each host exposing metrics, configure Prometheus to scrape all hosts [OK]

Hint: One cAdvisor per host, Prometheus scrapes all [OK]

Common Mistakes:

• Thinking one cAdvisor can monitor all hosts
• Running multiple Prometheus instances unnecessarily
• Ignoring multi-host scraping config