Cross-cloud networking cost: the price of multi-cloud connectivity

Quick answer

Connecting workloads across clouds is expensive because data moving between clouds incurs egress on the source side (and sometimes ingress or processing on the destination), plus the cost of the interconnect (dedicated interconnect, VPN, or partner connection) that links them, and it adds latency. So cross-cloud data movement is effectively billed as egress on the sending cloud every time. The main lever is architectural: minimize data moving between clouds, colocate tightly-coupled workloads on one cloud, and only span clouds where the benefit justifies the transfer cost.

Multi-cloud architectures, running workloads across AWS, Azure, and GCP, sound flexible but carry a real networking cost: moving data between clouds is billed as egress on the source cloud, plus the interconnect linking them, plus added latency. So cross-cloud data movement is one of the more expensive networking patterns, and minimizing it is the main discipline.

Where cross-cloud cost comes from

Component	Cost
Source egress	Data leaving the source cloud (billed per GB)
Interconnect	Dedicated interconnect / VPN / partner link
Latency	Added round-trip between clouds

The dominant cost is source-side egress: every gigabyte leaving a cloud to reach another is billed at that cloud's egress rate. Add the interconnect (a dedicated connection, VPN, or partner interconnect linking the clouds) and the latency of traffic crossing between providers. So chatty cross-cloud communication is expensive on both cost and performance.

Minimize cross-cloud data movement

The main lever is architectural: colocate tightly-coupled workloads (services that talk to each other frequently, and their data) on one cloud so their traffic stays in-cloud (cheap or free), and only span clouds at boundaries where data movement is minimal. Replicating large datasets across clouds, or chatty inter-service calls across clouds, are the expensive antipatterns, keep those within one cloud.

Controlling cross-cloud networking cost

Minimize data moving between clouds (the biggest lever), colocate tightly-coupled workloads and their data on one cloud, span clouds only at low-traffic boundaries, avoid replicating large datasets across clouds, use interconnects that price cross-cloud traffic below public egress where the volume justifies them, and weigh the multi-cloud benefit against the transfer cost. Because cross-cloud movement is billed as egress every time, designing to keep data and chatty traffic within one cloud is the discipline, an extension of egress optimization.

FAQ

Why is cross-cloud networking expensive?

Because data moving between clouds incurs egress on the source cloud (billed per GB at that cloud's egress rate) every time, plus the cost of the interconnect (dedicated connection, VPN, or partner link) that links them, plus added latency. So cross-cloud data movement is effectively billed as egress on the sending cloud, making chatty cross-cloud communication expensive on both cost and performance.

How do I reduce cross-cloud networking cost?

Minimize data moving between clouds (the biggest lever), colocate tightly-coupled workloads and their data on one cloud so traffic stays in-cloud, span clouds only at low-traffic boundaries, avoid replicating large datasets across clouds, use interconnects that price cross-cloud traffic below public egress where volume justifies them, and weigh the multi-cloud benefit against the transfer cost.

What is the main cost of multi-cloud connectivity?

Source-side egress: every gigabyte leaving a cloud to reach another is billed at that cloud's egress rate, so cross-cloud data movement accrues egress charges continuously. Added to that is the interconnect linking the clouds and the latency of cross-provider traffic. The egress dominates, which is why minimizing cross-cloud data movement is the key lever.

Should I colocate workloads on one cloud?

For tightly-coupled workloads, yes. Services that talk to each other frequently, and their data, should be colocated on one cloud so their traffic stays in-cloud (cheap or free) rather than crossing clouds (billed as egress). Spanning clouds is best reserved for boundaries where data movement is minimal, avoiding chatty inter-service calls or large data replication across clouds.

Is multi-cloud worth the networking cost?

It depends on why you are multi-cloud. Genuine benefits (avoiding lock-in, using best-of-breed services, regulatory or resilience requirements) can justify the cross-cloud networking cost if you architect to minimize data movement between clouds. But multi-cloud adopted without minimizing cross-cloud traffic pays significant egress for little benefit, so weigh the benefit against the transfer cost.

Does C3X estimate cross-cloud networking cost?

C3X prices infrastructure across clouds from your Terraform, including interconnects and the resources on each cloud, so the fixed connectivity cost appears before deploy. Cross-cloud data transfer (egress) depends on how much data moves between clouds, which you provide as a usage assumption, since it is the dominant and most avoidable cost.

What to do next

Price your multi-cloud architecture before you build it. C3X reads your Terraform and prices your resources against a live catalog. Start with the quickstart.