Bridging the Gap: Choosing Your Highway to Google Cloud
In the world of Hybrid Cloud, the “Last Mile” isn’t just about distance—it’s about reliability, speed, and security. When connecting your on-premises data center to Google Cloud Platform (GCP), architects are faced with a critical decision: Cloud VPN or Cloud Interconnect?
For many startups, Cloud VPN is the entry point. It’s quick to set up and uses the public internet to create an encrypted tunnel. However, as enterprises scale, the unpredictability of the public internet becomes a bottleneck. This is where HA VPN (High Availability VPN) shines, offering a 99.99% SLA by mandating two interfaces and two tunnels.
But what if you need more than just encryption? What if you need consistent 100Gbps throughput and low-latency “line-rate” performance? Enter Cloud Interconnect. Whether you choose Dedicated Interconnect (a physical wire from your router to Google’s) or Partner Interconnect (leveraging a provider like Equinix), you are essentially extending your private network into the cloud, bypassing the public internet entirely.
In this guide, we will break down the architectural nuances that separate a “good” hybrid setup from an “enterprise-grade” powerhouse.
Study Guide: GCP Hybrid Connectivity
The Analogy
Imagine you need to move goods between two offices across a busy city.
- Cloud VPN: Is like driving an armored truck on the public highway. It’s secure (encrypted), but you’re at the mercy of traffic jams (internet congestion).
- Dedicated Interconnect: Is like building a private underground subway line between your two buildings. No traffic, maximum speed, but very expensive to build.
- Partner Interconnect: Is like renting space on an existing private railway owned by a third party.
Detailed Explanation
1. Cloud HA VPN
HA VPN is the modern standard for VPNs in GCP. It requires a Cloud Router and provides two public IP addresses. To achieve the 99.99% SLA, you must configure two tunnels from your on-prem gateway to these two GCP interfaces. It uses IPsec for encryption and BGP (Border Gateway Protocol) for dynamic routing.
2. Dedicated Interconnect
This provides a direct physical connection between your on-premises network and Google’s network. You must meet Google at a specific colocation facility. It offers 10 Gbps or 100 Gbps circuits. It does not encrypt traffic by default (though you can layer HA VPN over Interconnect for “MACsec” or IPsec encryption).
3. Partner Interconnect
Ideal for organizations whose data centers are not in a Google colocation facility. You connect to a supported service provider, who handles the physical link to Google. Bandwidth is flexible, ranging from 50 Mbps to 50 Gbps.
Real-World Scenarios
- Scenario A: A small retail company needs to sync daily backups to GCS. Solution: HA VPN. Cost-effective and sufficient for bursty traffic.
- Scenario B: A high-frequency trading firm requires sub-5ms latency and 40Gbps throughput. Solution: Dedicated Interconnect.
- Scenario C: A branch office in a remote region needs to access VPC resources but isn’t near a Google Point of Presence (PoP). Solution: Partner Interconnect.
Comparison Table
| Feature | HA VPN | Dedicated Interconnect | Partner Interconnect | AWS Equivalent |
|---|---|---|---|---|
| Medium | Public Internet | Private Fiber | Service Provider | – |
| Bandwidth | Up to 3 Gbps/tunnel | 10 Gbps or 100 Gbps | 50 Mbps to 50 Gbps | Direct Connect / Site-to-Site VPN |
| SLA | 99.99% | 99.9% or 99.99% | 99.9% or 99.99% | Varies |
| Encryption | IPsec (Standard) | None (Optional MACsec) | None (Optional IPsec) | AWS DX (No encryption by default) |
Interview Questions & Answers
- Q: What is the minimum number of tunnels required for HA VPN SLA?
A: Two tunnels are required to achieve the 99.99% availability SLA. - Q: Does Cloud Interconnect encrypt data in transit?
A: No, it provides a private circuit but not encryption. For encryption, you must use HA VPN over Interconnect. - Q: When would you choose Partner Interconnect over Dedicated?
A: When your physical data center is not in a Google colocation facility or when you need less than 10 Gbps. - Q: What routing protocol is required for HA VPN and Interconnect?
A: BGP (Border Gateway Protocol) is required for dynamic routing. - Q: What is a VLAN Attachment?
A: It is a logical connection (virtual circuit) between your on-prem network and a single region in your VPC via Interconnect. - Q: How do you scale VPN bandwidth beyond 3 Gbps?
A: By creating multiple tunnels and using ECMP (Equal-Cost Multi-Path) routing. - Q: Can HA VPN connect to a non-GCP cloud?
A: Yes, it is commonly used for Multi-cloud connectivity (e.g., GCP to AWS). - Q: What is the “MTU” issue often discussed with VPNs?
A: IPsec overhead reduces the effective MTU (usually to 1460 bytes). If not accounted for, packets may be dropped. - Q: What is the difference between Layer 2 and Layer 3 Partner Interconnect?
A: Layer 2 requires you to configure BGP on your on-prem router; Layer 3 means the partner handles BGP for you. - Q: What is the “99.99% topology” for Interconnect?
A: It requires two connections in one metro (City A) and two connections in a different metro (City B).
- The “BGP” Gotcha: Always mention that Cloud Router is a control-plane element only; it doesn’t handle the data traffic, but it manages the BGP sessions.
- Cost Trade-off: VPN has low upfront cost but high egress costs. Interconnect has high fixed costs but significantly lower data egress rates.
- IPv6: HA VPN supports IPv6, but ensure your on-premise gateway supports IKEv2.
Visual Architecture: Hybrid Connectivity
Cloud Router: Mandatory for BGP exchange.
Cloud Armor: Can be used to protect hybrid endpoints.
Shared VPC: Connect multiple projects to one Interconnect.
- VPN: 3 Gbps per tunnel. Scale with more tunnels.
- Dedicated: 10G or 100G per link. Max 8 links per bundle (800Gbps).
- Latency: Interconnect provides deterministic “predictable” latency.
- VPN: $0.05/hr per tunnel + standard egress rates.
- Interconnect: High monthly port fee + lower “Interconnect Egress” rates.
- Tip: Use Interconnect if moving >10TB data monthly to save on egress.
Production Use Case
Global Media Streaming: A company uses Dedicated Interconnect at their primary production studio for massive 4K video uploads (100Gbps) and HA VPN as a failover/backup path. They use Cloud Router with Global Dynamic Routing to ensure traffic automatically reroutes to the VPN if the fiber is cut.