Multicloud Networking: Connecting OCI to Azure

A large share of enterprises run their Oracle databases where Oracle runs best, on OCI, while their applications, analytics and developer platforms live on Azure. That split is deliberate and it works well, but it only works if the network between the two clouds is fast, private and predictable. This guide covers the ways to connect OCI and Azure, the trade offs, and how to design routing across the boundary.

Why this pattern exists

The OCI and Azure combination grew out of a partnership between the two providers that produced a direct, low latency interconnect between specific regions. For organisations that already invested in Azure for their application estate but want Oracle databases on the infrastructure engineered for them, the pattern gives the best of both. The database tier sits on OCI, the application tier sits on Azure, and the interconnect carries the traffic between them at latency low enough for many production workloads.

The decision to adopt it is rarely purely technical. Licensing, existing commitments and team skills all weigh in. The networking job is to make the chosen split perform as if it were one estate.

The connection options

Where it is available, the Oracle Interconnect for Azure is the cleanest option because it is a purpose built private path between paired regions with no third party in the middle. When the regions you need are not paired, the equivalent result comes from provisioning FastConnect on the OCI side and ExpressRoute on the Azure side and meeting them at a shared partner. VPN over the internet remains the fast to deploy fallback for low volume or test traffic, with the usual caveats about variable latency.

A design framework for OCI to Azure

Latency is the deciding factor

The thing that makes or breaks this pattern is the conversation between the application and the database. A workload that issues many small queries per request amplifies any latency between the tiers, so even a fast cross region link can hurt if the application was written assuming the database was a millisecond away. Geographically paired regions keep that latency to a minimum, which is why the supported region pairs matter so much. Where the application is chatty, consider reducing round trips at the application layer in addition to optimising the link. The principles in network performance tuning apply directly here.

Routing and address planning

Routing across two clouds follows the same discipline as connecting to on premises. Advertise only the ranges that need to cross, keep address space from overlapping between the OCI VCN and the Azure virtual network, and prefer dynamic routing so failover between redundant paths is automatic. If many OCI networks need to reach Azure, terminate the interconnect on a single DRG and use transit routing so every spoke shares the path. The same private connectivity discipline covered in private connectivity patterns applies across the cloud boundary.

Security and operations

Treat the other cloud as an external but trusted network. Use network security groups on the OCI side and the equivalent controls on Azure so that only the specific application subnets can reach only the specific database ports. Encrypt sensitive traffic at the application or transport layer, since a private interconnect is private but not necessarily encrypted. Monitor both ends, because a problem on the Azure side can present as an OCI database timeout and waste hours of investigation if you only watch one cloud.

Designing the application for the split

The cleanest cross cloud networking cannot rescue an application that was written assuming its database is on the same machine. When the application tier on Azure and the database tier on OCI are separated by even a few milliseconds, every avoidable round trip is multiplied across the link. An application that fetches a row, then fetches a related row, then another, in a tight loop, will feel the separation badly. One that batches its work into fewer, larger calls will barely notice. So part of designing for this pattern is reviewing how the application talks to the database, and reducing the number of round trips where you can, through batching, caching read heavy data near the application, and avoiding patterns that issue many tiny queries per request.

This is why the pattern suits some workloads far better than others. A reporting or analytics application that issues a modest number of substantial queries is an excellent fit. A legacy application built around thousands of small interactions per page is a harder one, and may need refactoring before the split performs acceptably. Be honest about which kind of workload you have before committing the architecture, because the network can only do so much for a chatty design.

Observability across two clouds

Operating a workload that spans OCI and Azure means you cannot rely on either provider's tools alone to see the whole picture. A database timeout reported on OCI might originate in an Azure network event, and an application error on Azure might trace back to an OCI side problem. Without observability on both ends and a way to correlate them, an incident becomes a finger pointing exercise between two consoles. Instrument both sides, capture metrics and logs from the interconnect, and make sure that when something goes wrong you can follow a single request across the boundary rather than guessing which cloud is at fault.

The same applies to change. A routing or security change on the Azure side can break connectivity to OCI just as easily as a change on the OCI side, so the two clouds need to be operated as one system with coordinated change control. Treating them as separate estates that happen to be connected is how a routine change in one cloud becomes an unexplained outage in the other.

When the direct interconnect is not available

Not every pair of regions supports the purpose built interconnect, and when yours does not, the meet in the middle approach using FastConnect on the OCI side and ExpressRoute on the Azure side gives an equivalent private path. The extra consideration is the partner or colocation facility where the two circuits meet, which becomes part of your path and part of your resilience story. Choose a partner with the reach and reliability your workload needs, design for redundancy across that meeting point if the workload demands it, and remember that you now have three parties in the path rather than two, which is more to monitor and more to coordinate during an incident.

Making multicloud feel like one estate

A well built OCI to Azure connection disappears into the background. The application on Azure reaches the database on OCI at predictable latency, the address plans never collide, and security at the boundary is tight. Achieving that is a matter of confirming region pairing, choosing the right link, planning addresses across both clouds, and measuring latency against the application's real behaviour. For how this fits the wider network design, see the complete OCI networking guide. When a multicloud estate has to perform and stay secure across the boundary, our OCI networking solution covers the design and validation end to end.