We have recently setup a virtual network that consists of one virtual machine (A3) running MSSQL, and one cloud service (Medium) running a web role.

Our web role will connect to the database using the internal network IP which works fine.

The issue were having is when we try load testing the app the network traffic being sent to the database is high and will fluctuate between 6-9 Mbps but will never go any higher. We are running Wireshark so can monitor when the requests that come into the web role which have no latency but the database requests are taking to long to send over the network.

If we run two instances of the web role we can send roughly double the network traffic to the database vm with out any issues.

Our app is using Entity Framework and our target is to process 25 requests per second with about 10 database calls per request.

Q1: Is there a max bandwidth rate between web roles and a vm using TCP on Azure?

Q2: How can we increase throughput between the cloud service and the database?


Since you're using a web role, I would assume that it is connected to your VNet by means of using a VPN gateway and a Point-to-Site tunnel, as stated here: https://azure.microsoft.com/en-us/blog/azure-websites-virtual-network-integration/

Here's the problem, the published information from Microsoft about their network speeds are as follow:

  1. They never reveled the speed of their inter VNet communication.
  2. They never reveled the speed of their Point-to-Site speed assuming that you're connected from a web app.
  3. The only piece of information you can live with is that the VPN gateway throughput is 100 Mbps, said here: https://azure.microsoft.com/en-us/documentation/articles/vpn-gateway-about-vpngateways/

Now, since (again assuming) that your app is connected using a Point-to-Site connection, the Azure documentation doesn't give any clue or SLA to how much bandwidth you should be getting, or if there is any way to improve the speed of your communication as stated in the Azure VPN FAQ from here: https://azure.microsoft.com/en-us/documentation/articles/vpn-gateway-vpn-faq/

Q: How much throughput can I expect through site-to-site or point-to-site connections?

A: It's difficult to maintain the exact throughput of the VPN tunnels. IPsec and SSTP are crypto-heavy VPN protocols. Throughput is also limited by the latency and bandwidth between your premises and the Internet.

The only possible way for this to be answered is for you to ask the Azure support team directly.

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