GCP Compute Engine SLA: Google Cloud's VM Uptime Guarantee

GCP Compute Engine SLA Overview

Google Cloud Platform's Compute Engine offers availability guarantees that reward multi-zone deployments, with a unique advantage: live migration for most maintenance events.

GCP Compute Engine SLA Tiers

Deployment Type	SLA	Monthly Downtime Allowed
Multi-zone (across zones)	99.99%	~4.4 minutes
Single Instance	99.5%	~3.6 hours

GCP's Live Migration Advantage

One of GCP's most distinctive features is live migration. During routine maintenance, GCP moves running VMs to other physical hosts without rebooting them. This means:

• Most maintenance events cause zero perceived downtime
• Your application processes continue running during migration
• Network connections are preserved (brief packet loss possible)
• Only certain maintenance events (security patches requiring reboot) cause actual downtime

What Counts as Downtime?

GCP measures instance-level availability. An instance is considered unavailable when it cannot be reached via its network interfaces. Scheduled maintenance events handled by live migration do not count as downtime.

Service Credits

Monthly Uptime %	Service Credit
99.0% - 99.99%	10% credit
95.0% - 99.0%	25% credit
< 95.0%	50% credit

Multi-Zone Architecture on GCP

For the 99.99% SLA, you need instances across multiple zones within a region:

Region: us-central1
├── Zone: us-central1-a  →  Instance Group A
├── Zone: us-central1-b  →  Instance Group B
└── Zone: us-central1-c  →  Instance Group C
    └── Cloud Load Balancer distributes traffic

GCP vs AWS vs Azure Comparison

Feature	GCP	AWS	Azure
Multi-zone SLA	99.99%	99.99%	99.99%
Single instance SLA	99.5%	99.5%	99.9% (Premium SSD)
Live migration	Yes	Limited	Limited
Max service credit	50%	100%	100%