Prometheus is an open-source monitoring and alerting toolkit designed for reliability and scalability. Key differences from traditional monitoring systems:

• Pull-based model: Prometheus scrapes metrics from targets rather than receiving pushed data
• Time-series database: Built-in TSDB optimized for metric storage
• Multi-dimensional data model: Metrics identified by metric name and key-value pairs (labels)
• Powerful query language: PromQL for flexible data analysis
• Service discovery: Automatic target discovery from various sources
• No external dependencies: Self-contained system

Traditional systems often use push-based models, require external databases, and have less flexible data models.

Prometheus architecture consists of several key components:

• Prometheus Server: Core component that scrapes and stores metrics, serves queries
• Client Libraries: For instrumenting application code to expose metrics
• Pushgateway: For short-lived jobs that can't be scraped directly
• Exporters: Proxy metrics from third-party systems (node_exporter, blackbox_exporter)
• Alertmanager: Handles alerts sent by Prometheus, manages routing, grouping, and notifications
• Service Discovery: Mechanisms to automatically discover targets
• Grafana: Common visualization layer (though separate project)

Prometheus supports four core metric types:

1. Counter: Cumulative metric that only increases (or resets to zero). Used for requests served, errors occurred, etc.
2. Gauge: Metric that can go up and down. Used for temperature, memory usage, concurrent requests
3. Histogram: Samples observations and counts them in configurable buckets. Also provides sum and count
4. Summary: Similar to histogram but calculates configurable quantiles over a sliding time window

Example:

# Counter
http_requests_total{method="GET",status="200"} 1234

# Gauge  
memory_usage_bytes 8589934592

# Histogram
http_request_duration_seconds_bucket{le="0.1"} 100
http_request_duration_seconds_bucket{le="0.5"} 150

Multiple installation methods:

Binary Installation:

# Download and extract
wget https://github.com/prometheus/prometheus/releases/download/v2.45.0/prometheus-2.45.0.linux-amd64.tar.gz
tar xvfz prometheus-*.tar.gz
cd prometheus-*

# Create user and directories
sudo useradd --no-create-home --shell /bin/false prometheus
sudo mkdir /etc/prometheus /var/lib/prometheus
sudo chown prometheus:prometheus /var/lib/prometheus

# Copy binaries and config
sudo cp prometheus promtool /usr/local/bin/
sudo cp -r consoles/ console_libraries/ /etc/prometheus/
sudo cp prometheus.yml /etc/prometheus/
sudo chown -R prometheus:prometheus /etc/prometheus/

Package Manager:

# Ubuntu/Debian
sudo apt update && sudo apt install prometheus

# RHEL/CentOS
sudo yum install prometheus

Docker:

docker run -p 9090:9090 prom/prometheus