Module 4: Keeping Systems Reliable

Overview

Master reliability concepts, high availability, load balancing, auto-scaling, and disaster recovery in Azure.

Lesson 4.1: What is Reliability? (SLI, SLO, SLA)

• SLA: Service Level Agreement (promise to customers)
• SLO: Service Level Objective (internal reliability target)
• SLI: Service Level Indicator (actual measurement)
• Analogy: Pizza delivery service (SLA/SLO/SLI)
• Demo: Create a slide or graphic explaining SLA/SLO/SLI

Lesson 4.2: High Availability in Azure

• Availability Zones and Sets
• Demo: Create VM in Availability Set

az vm availability-set create --resource-group DemoGroup --name DemoAvailSet
az vm create --resource-group DemoGroup --name DemoVM1 --availability-set DemoAvailSet --image UbuntuLTS --admin-username azureuser --generate-ssh-keys

Lesson 4.3: Load Balancers & Auto-Scaling

• Load Balancer, Traffic Manager, Auto-Scaling
• Demo:

az network lb create --resource-group DemoGroup --name DemoLB --sku Basic --frontend-ip-name DemoFrontEnd --backend-pool-name DemoBackEndPool
az vmss create --resource-group DemoGroup --name DemoScaleSet --image UbuntuLTS --upgrade-policy-mode automatic

Lesson 4.4: Backup & Disaster Recovery (DR)

• Azure Backup and Site Recovery
• Demo:
  • Enable Azure Backup for a VM
  • Restore deleted file from backup

Assessment

• Quiz and reliability scenario lab

Troubleshooting Tips & Common Mistakes

• Always use Availability Sets for VMs to avoid single points of failure.
• If load balancing fails, check backend pool configuration and health probes.
• Common mistake: Not enabling backup before data loss occurs.
• Test disaster recovery regularly, not just once.

Visual Guide

Sample high availability architecture.

Quick Quiz

1. What is the difference between SLA, SLO, and SLI?
2. How does Azure Load Balancer improve reliability?
3. Why is disaster recovery important?

Discuss your answers in the course forum or with your instructor.

Community & Discussion

• Join the Azure SRE Learners Forum to ask questions, share projects, and connect with peers.

Goal: Apply reliability concepts to a simple Azure deployment.

Tasks:

1. Deploy two VMs in an Availability Set.
2. Set up a Load Balancer to distribute traffic between the VMs.
3. Enable Azure Backup for one VM and perform a backup.
4. Simulate a failure by stopping one VM and observe load balancing.
5. Restore a deleted file from backup.

Submission:

• Provide screenshots and a brief report on how reliability was achieved.

Hands-On Assignment

Scenario: You are designing a reliable web service for a client.

Instructions:

1. List three strategies to ensure high availability and disaster recovery.
2. Explain how you would use Azure services to implement these strategies.
3. Share your plan in the course forum or with your instructor.

Resources

• Azure Reliability Documentation
• Azure Backup
• Azure Site Recovery