MODULE 3 - EC2 Troubleshooting

Overview

This module is dedicated to troubleshooting EC2 instances. You will learn to diagnose and resolve common issues related to the creation and operation of instances.

Learning Objectives

By the end of this module, you will be able to:

• Identify common instance creation errors
• Apply the diagnostic method: symptom → hypotheses → tests → fix
• Read and interpret EC2 states and events
• Resolve connectivity issues (SSH, HTTP)
• Analyze basic logs and metrics

Week Content

1. Instance Creation Errors

• InsufficientInstanceCapacity
• InstanceLimitExceeded
• Security Group Errors
• Subnet and VPC Issues

2. Diagnostic Method

┌─────────────────────────────────────────────────────────────┐
│              DIAGNOSTIC METHOD                              │
├─────────────────────────────────────────────────────────────┤
│                                                              │
│   1. SYMPTOM                                                 │
│      └── What exactly is not working?                       │
│                                                              │
│   2. HYPOTHESES                                              │
│      └── What are the possible causes?                      │
│          (Network? Security? Instance? Application?)        │
│                                                              │
│   3. TESTS                                                   │
│      └── How to verify each hypothesis?                     │
│          (ping, curl, logs, metrics)                        │
│                                                              │
│   4. FIX                                                     │
│      └── What action resolves the issue?                    │
│                                                              │
│   5. DOCUMENTATION                                           │
│      └── Note the solution for future reference             │
│                                                              │
└─────────────────────────────────────────────────────────────┘

3. Common Issues and Solutions

Problem	Probable Cause	Solution
Cannot SSH	Security Group port 22	Add SSH rule
Instance "pending" long time	Region capacity	Change AZ or type
Instance stops immediately	AMI/EBS issue	Check system logs
No public IP	Subnet without auto-assign	Enable or use EIP
HTTP not responding	Service not started	Check application

4. Reading EC2 States

States and their meaning:

pending     → Starting up (normal < 2 min)
running     → Instance operational
stopping    → Stopping in progress
stopped     → Stopped (no compute billing)
terminated  → Permanently deleted

System status codes (Status Checks):
- System Status: AWS issue (network, hardware)
- Instance Status: Your config issue (OS, instance network)

Troubleshooting Exercises

Exercise 1: Cannot SSH

Scenario:
You launched an EC2 instance but cannot connect via SSH.
The command `ssh -i key.pem ec2-user@IP` times out.

Questions:
1. What are your top 3 hypotheses?
2. How do you verify them?
3. What is the most probable cause?

Exercise 2: Website Inaccessible

Scenario:
Your Apache web server is installed on EC2.
You can SSH but http://IP does not respond.

Questions:
1. Is the issue network or application related?
2. What commands do you use to diagnose?
3. Propose 3 possible solutions.

Deliverables

Mini-Troubleshooting Report

For 2 failure scenarios (given in class), document:

• The observed symptom
• The formulated hypotheses
• The tests performed
• The applied fix
• The lessons learned

Evaluation

Type: Formative (0%)

• Guided troubleshooting exercise in class
• Scenario analysis

Navigation

1. Common Errors - Creation issues
2. Diagnostic Method - Structured approach
3. Validation Quiz - 30 questions to validate your knowledge
4. Lab: Failure Scenarios - Practical exercises

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Next week: MODULE 4 - EBS Storage