☁️ Availability and High Availability on Google Cloud Platform

🔍 What is Availability?

Availability is a simple yet crucial metric:

Is your application accessible when users need it?

It’s defined as the percentage of time your app delivers the operations expected from it.
For example:

• 99.99% availability → app is down < 4.5 minutes per month
• 99.999% → just 26 seconds of downtime per month!

These are known as “four nines” or “five nines” availability.

📉 Availability Table Example

🤯 Why Availability Is Hard

If your app requires 99.95% availability but you release 5 times a month, each taking 5 minutes…
That’s 25 minutes of downtime.
🚫 You already broke the SLA.

🏗️ High Availability on GCP

To achieve high availability, you must think beyond frontend:

Your app = frontend + backend + APIs + DB + services
All must be up to meet availability targets.

🧱 Strategy 1: Regional Instance Groups

Distribute your Compute Engine VMs across zones in a region to survive zonal failures.

🌍 Strategy 2: Global Load Balancing

Create instance groups in multiple regions
→ Use Global HTTPS Load Balancer
→ Distributes load automatically across regions

🩺 Strategy 3: Health Checks

• Auto-detect and replace failing instances
• Use health checks at instance group level and LB level

🔄 Strategy 4: Live Migration

Enable live migration in Compute Engine
→ VM updates don’t require downtime

✅ GCP Makes It Easier

• Google’s Load Balancer is fully managed
• Auto healing happens with no manual action
• Services scale automatically with traffic

💡 Real World Benefit

This kind of setup can survive:

• 🔥 Zonal outages
• ⚡ Regional failures
• 🧑‍💻 Updates and patches without interrupting users

❓ Interactive Quiz