What is Prometheus, and why is it used?

Prometheus is an open-source monitoring and alerting system used to collect metrics from applications and infrastructure. It is widely used because of its pull-based model, powerful query language (PromQL), and time-series database capabilities.

Example Use Case:

• Monitoring CPU, memory, and network usage
• Collecting application performance metrics
• Alerting on high error rates or latency

How does Prometheus collect data?

Prometheus pulls metrics from target endpoints exposed via HTTP at /metrics. The targets can be defined in a static configuration or discovered dynamically (e.g., Kubernetes service discovery).

Example scrape configuration (prometheus.yml):

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

What is PromQL?

PromQL (Prometheus Query Language) is used to query and analyze metrics stored in Prometheus. It enables users to create alerts, dashboards, and graphs.

Example Queries:

• CPU usage:

  node_cpu_seconds_total{mode="user"} / sum(node_cpu_seconds_total) * 100

• Request rate:

  rate(http_requests_total[5m])

What are Prometheus exporters?

Exporters are agents that collect and expose metrics from various applications and systems.

Common Exporters:

• Node Exporter (system metrics)
• Blackbox Exporter (network probes)
• MySQL Exporter (database metrics)

How do you set up an alert in Prometheus?

Alerts are configured in alerting_rules.yml and evaluated by the Alertmanager.

Example Rule:

groups:
  - name: instance_down
    rules:
      - alert: InstanceDown
        expr: up == 0
        for: 5m
        labels:
          severity: critical
        annotations:
          description: "Instance {{ $labels.instance }} is down."

What is Grafana?

Grafana is an open-source analytics and visualization tool used to create interactive dashboards for monitoring data from Prometheus, ELK, and other sources.

How do you connect Grafana to Prometheus?

1. Login to Grafana (http://localhost:3000).
2. Navigate to "Configuration" → "Data Sources".
3. Select Prometheus as the data source.
4. Enter Prometheus URL (http://localhost:9090).
5. Click Save & Test.

What are Grafana Panels?

Panels are visual components in Grafana used to display data in various formats:

• Graph Panel: Time-series data visualization
• Single Stat Panel: Displays a single numeric value
• Table Panel: Tabular data display

How do you create alerts in Grafana?

1. Select a panel.
2. Click "Edit" → "Alert".
3. Define a condition using PromQL queries.
4. Set the evaluation interval (e.g., every 1m).
5. Configure the alert notification (Slack, Email, etc.).

How do you configure a Grafana dashboard using JSON?

Export and import dashboards using JSON files.

Example JSON snippet:

{
  "panels": [
    {
      "type": "graph",
      "title": "CPU Usage",
      "targets": [
        { "expr": "node_cpu_seconds_total", "format": "time_series" }
      ]
    }
  ]
}

What is the ELK Stack?

The ELK Stack consists of:

• Elasticsearch (search and analytics engine)
• Logstash (log processing pipeline)
• Kibana (visualization tool)

What is the role of Elasticsearch in ELK?

Elasticsearch is a NoSQL, distributed search engine used to store, search, and analyze log data.

How does Logstash work?

Logstash processes logs using a pipeline:

• Input: Reads logs (from files, databases, Kafka, etc.)
• Filter: Transforms logs (parse JSON, remove sensitive data)
• Output: Sends logs to Elasticsearch or other storage

Example Logstash Configuration:

input { file { path => "/var/log/syslog" } }
filter { grok { match => { "message" => "%{SYSLOGTIMESTAMP:timestamp}" } } }
output { elasticsearch { hosts => ["localhost:9200"] } }

What is Kibana used for?

Kibana is used to visualize and explore log data stored in Elasticsearch. It provides features like:

• Dashboards: Custom data visualizations
• Discover: Search raw logs
• Alerts: Set up log-based alerts

How do you install the ELK stack?

Install Elasticsearch, Logstash, and Kibana:

# Install Elasticsearch
sudo apt install elasticsearch

# Install Logstash
sudo apt install logstash

# Install Kibana
sudo apt install kibana