Prometheus for Docker monitoring - Practice Problems & Coding Challenges

Challenge - 5 Problems

💻 Command Output

intermediate

Prometheus Docker container startup output

You run the following command to start Prometheus in Docker with a custom configuration file. What is the expected output in the Docker logs indicating Prometheus started successfully?

Docker

docker run -d --name prometheus -p 9090:9090 -v /home/user/prometheus.yml:/etc/prometheus/prometheus.yml prom/prometheus

A level=warn ts=... msg="Deprecated flag used" ...

B Error: failed to load config file: open /etc/prometheus/prometheus.yml: no such file or directory

C level=info ts=... msg="Starting Prometheus" ...

D level=error ts=... msg="Failed to bind to port 9090" ...

💡 Hint

Look for a log message that confirms Prometheus started without errors.

When Prometheus starts successfully, it logs an info level message with 'Starting Prometheus'. Errors about config file or port binding indicate startup failure.

❓ Configuration

intermediate

Prometheus scrape config for Docker containers

Which Prometheus scrape configuration snippet correctly scrapes metrics from Docker containers exposing metrics on port 9100?

A

scrape_configs:
  - job_name: 'docker'
    static_configs:
      - targets: ['localhost:9100']

B

scrape_configs:
  - job_name: 'docker'
    docker_sd_configs:
      - host: 'unix:///var/run/docker.sock'
        port: 9100

C

scrape_configs:
  - job_name: 'docker'
    file_sd_configs:
      - files: ['/etc/prometheus/docker_targets.yml']

D

scrape_configs:
  - job_name: 'docker'
    kubernetes_sd_configs:
      - role: pod

💡 Hint

Docker service discovery uses the Docker socket and port configuration.

Option B uses docker_sd_configs with the Docker socket and port 9100, which is the correct way to discover Docker containers exposing metrics.

❓ Troubleshoot

advanced

Prometheus cannot scrape Docker container metrics

You configured Prometheus to scrape Docker containers on port 9100, but no metrics appear in Prometheus UI. Which is the most likely cause?

A Docker containers do not expose metrics on port 9100

B Prometheus configuration file has invalid YAML syntax

C Prometheus port 9090 is blocked by firewall

D Prometheus container lacks access to Docker socket

💡 Hint

Prometheus needs permission to access Docker socket for service discovery.

Without access to the Docker socket, Prometheus cannot discover containers to scrape metrics from, even if containers expose metrics correctly.

🔀 Workflow

advanced

Steps to monitor Docker containers with Prometheus

What is the correct order of steps to set up Prometheus monitoring for Docker containers exposing metrics on port 9100?

A 1,2,3,4

B 2,1,3,4

C 1,3,2,4

D 3,2,1,4

💡 Hint

Think about starting containers first, then Prometheus, then configuration, then verification.

You must first run containers exposing metrics, then start Prometheus with access to Docker socket, configure scraping, and finally verify in UI.

✅ Best Practice

expert

Best practice for Prometheus Docker monitoring security

Which option is the best practice to securely run Prometheus monitoring Docker containers without exposing the Docker socket to Prometheus container?

A Use a Prometheus exporter sidecar container per Docker container

B Mount the Docker socket read-only into Prometheus container

C Run Prometheus on the host machine with full Docker socket access

D Disable Docker socket access and scrape metrics via container IPs only

💡 Hint

Consider isolation and minimal permissions for security.

Using a sidecar exporter per container avoids giving Prometheus direct access to the Docker socket, improving security by isolating permissions.