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Costs are always a factor to consider in the cloud. For organizations adopting Azure as their cloud service provider, tools such as Azure calculator and Azure Migrate can help develop fairly accurate Azure cost management projections. However, network data transfer costs are not often factored in during resource planning.
Network charges can occur in different scenarios based on Azure resource placement as well as inter-component communication in the application. If you haven’t planned your Azure usage with these charges in mind, it could impact your monthly cloud bill significantly, especially in large-scale organizations with sprawling deployments in Azure.
This blog will focus on helping readers identify the hidden data transfer charges on Azure, which could otherwise be missed. We’ll also see how customers can leverage Cloud Volumes ONTAP to reduce these hidden Azure data transfer costs.
Data Transfer Costs in Azure: What Is Chargeable?
“Inbound data transfer to Azure data center is free,” reads the Azure bandwidth pricing website. This statement, though true for ingress traffic from the internet, causes many organizations to miss the big picture. There are other types of data transfers that will be reflected in your monthly bill; i.e. those charges for transfers between regions, availability zones, services, etc. Azure data transfer costs vary depending on the Azure zones from which the traffic originates. There are five such zones: Zone 1, Zone 2, Zone 3, DE Trustee, and US Gov. You can see all the regions mapped under each zone here.
Let’s now dive into the specifics of data transfer for various deployment scenarios.
Data transfers between Azure regions: There are no data transfer charges when services in the same region communicate with each other. However, the outbound data transfer charges kick in when an Azure service in one region communicates with an Azure service in another region.
The charges will depend on the Zone from which the traffic originates. The incoming traffic to the target service is still considered free. For example, a web server in Zone 1 Azure region communicating with a SQL Server deployed in a Zone 2 region will be charged at the rate of $0.087 per GB for data transfers up to 10 TB/month. For the next data transfer slab, i.e. up to 40 TB/month, the cost incurred will be $0.083 per GB.
Data transfers between Azure availability zones: Resources are deployed in availability zones to protect them from Azure data center-level outages. Azure offers an SLA of 99.99% for resources deployed in Azure availability zones, and hence is a preferred configuration while designing highly available architectures.
There are no data transfer charges when resources that are deployed in the same VNET and availability zone communicate with each other. The same is the case when the resources communicate to an Azure public endpoint in the same region. However, the data transferred between resources in different availability zones is chargeable, even if they are deployed in the same VNET. Note that both ingress and egress traffic is chargeable in this case.
Inter-network data transfer: When two Azure networks are connected through Azure VNET peering, both ingress and egress data transfers are chargeable even though the transfer happens within Azure’s backbone network.
VNET peering can be done in two ways: either between different networks within a single region or between networks that reside in different regions, the latter of which is referred to as Global VNET peering. The inbound and outbound data transfer charges are also different for these two VNET peering types. The Global VNET peering charges are dependent on the zone where the VNETs are provisioned. For example, if a VM in a VNET in Zone 1 initiates a data transfer to a VM in Zone 2, outbound charges for Zone 1 and inbound charges for Zone 2 will be applicable.
Outbound data transfer: The first 5 GB per month of outbound data transfer is free for all Azure zones, but following that the Azure pricing tiers will kick in based on various slabs (5–10 TB, then 40TB, 100TB, 350TB, and then everything above 500 TB).
This charge should be considered if the applications deployed in Azure are accessed over the internet. For example, when downloading data from Azure storage accounts or websites, accessing VMs over RDP and SSH will incur charges as data is being transferred out of an Azure data center.
Another scenario where these charges will be applied is with hybrid connectivity through VPN or ExpressRoute. For VPNs, the outbound data from the VPN Gateways will be billed at outbound data charge rates. For ExpressRoute, outbound data transfers are chargeable for metered data plans, and the cost will vary based on the selected plan.
Optimizing Your Network Data Transfer Charges
Azure cost optimization for network data transfer should be planned out well before the workload deployments. The crux of the process is understanding the various cost components that we discussed in the earlier section and tweaking the data flow to compensate without impacting application performance or availability.
Resource Placement
Data transfer costs come into the picture mainly when resources are dispersed across multiple regions or availability zones. Within the same region and availability zone, the data flow is free of cost. Also, the charges vary across different regions and zones. Unless mandated by compliance or security requirements, choose the Azure region that offers lowest data transfer rates. For DR and Azure high availability scenarios for production workloads, it might be required to deploy resources across multiple regions or availability zones. However, for other environments the network traffic charges can be minimized by deploying resources in the same region and availability zone.
Leverage the Azure Pricing Calculator
Once the resource placement has been done to implement a route with lower network data transfer cost, you can add the details to the Azure pricing calculator to get a near accurate projection of the monthly cloud bill. Continuous monitoring of the charges through the Azure cost management service is also recommended to identify additional optimization opportunities.
Limit Egress Through Private IPs
It is recommended to reduce the number of public IP addresses in an architecture, which is beneficial both from a cost as well as security perspective. Using private IPs ensures that the traffic remains within a VNET and other networks connected to it. By avoiding outbound data transfers to the internet as much as possible in the deployment, the egress data charges can be avoided.
Azure CDN for Large-Scale Data Transfers
As a content delivery network, Azure Content Delivery Network (Azure CDN) helps deliver content to users faster. Azure CDN does this by caching high-bandwidth content on edge servers that are located closer to the users than the primary storage location is. This makes it a good option for large-scale data transfers.
Data transfers from Azure services to Azure CDN are free of charge. Customers can consider Azure CDN for applications with higher outbound data transfer requirements, such as streaming services, for example. The cost of outbound transfer from Azure CDN is dependent on the Azure zone, and the cost benefit would vary accordingly.
For example, direct outbound data transfer of 10–50 TB/month can cost $0.087 per GB, whereas the same slab would cost you only $0.075 per GB in Zone 1 while using Azure Content Delivery Network Standard SKU.
Implementing Cost Control with Cloud Volumes ONTAP
Cloud Volumes ONTAP brings the capabilities of trusted ONTAP storage platform to Azure. With advanced data management capabilities, Cloud Volumes ONTAP gives applications a distinctive edge when compared to traditional cloud storage services. Cloud Volumes ONTAP delivers a truly hybrid storage deployment experience that helps you manage on-premises as well as cloud storage through a single management pane.
How can this benefit when it comes to data transfers? Cloud Volumes ONTAP implements storage economy through proprietary features like thin provisioning, deduplication and compression that reduces cloud data storage costs and footprint by 50-70%. With the more compact data size, the lower the transfer costs. This also extends to the SnapMirror® data replication feature, which enables seamless Azure migration with minimal storage overhead.
These storage efficiency features offered by Cloud Volumes ONTAP helps to reduce the data moving across Azure deployments or to on-premises during events like snapshot restore or DR. You can confidently migrate data across environments, without worrying about huge data egress costs that might otherwise add up and become a major concern.
Conclusion
Customers can rein in Azure data transfer costs by implementing the right optimization solutions as discussed in this blog. Advanced storage management capabilities offered by Cloud Volumes ONTAP complements this effort and helps to effectively lower the hidden network transfer charges in your monthly cloud bill. 
