06 Monitoring - C# Mastery Hub

📖 What is Monitoring?

Monitoring means watching your system all the time. You collect data about CPU, memory, errors, and speed. If something goes wrong, you get an alert.

💡 Simple Example:
Think of a hospital patient. The heart monitor beeps if something is wrong. Monitoring is the heart monitor for your app.

🤔 Why Monitor?

Find problems early — Before users complain.
Understand performance — See what is slow and why.
Plan for growth — Know when to add more servers.
Prove reliability — Show uptime to clients.

🌍 Real Client Example

Client: An online learning platform with 50,000 students.

Problem: Every Monday morning, the site becomes very slow. Students complain. The client does not know why.

Solution with Monitoring:

Set up Prometheus to collect CPU, memory, and request data.
Set up Grafana dashboards to see the data visually.
Add alerts that send an email if CPU goes above 80%.
Found the problem: a nightly report was running during peak hours.

Result: We moved the report to 3 AM. The site is fast on Monday mornings. Students are happy.

🛠️ Key Monitoring Tools

Prometheus

Collects numbers (metrics) from your app. Stores them over time.

Grafana

Shows the numbers in beautiful dashboards.

ELK Stack

Collects and searches log files.

Alertmanager

Sends alerts by email, Slack, or SMS.

📈 Example: Key Metrics to Watch

Metric	What It Means	Good Value
CPU Usage	How busy the CPU is	Below 70%
Memory Usage	How much RAM is used	Below 80%
Response Time	How long a request takes	Below 500 ms
Error Rate	Percentage of failed requests	Below 1%
Uptime	Time the system is online	Above 99.9%

✍️ Your First Alert Rule

This Prometheus rule sends an alert if CPU is too high for 5 minutes:

groups:
- name: example
  rules:
  - alert: HighCpuUsage
    expr: cpu_usage > 80
    for: 5m
    labels:
      severity: warning
    annotations:
      summary: "CPU usage is above 80% for 5 minutes"

What this does:

expr — The condition (CPU above 80%).
for — Must be true for 5 minutes.
labels — Mark the alert type.
annotations — A message to send.

✅ What You Learned

Monitoring watches your system all the time.
Prometheus collects numbers. Grafana shows them.
Alerts tell you when something is wrong.
Good to watch: CPU, memory, response time, errors, uptime.

📊 Monitoring