Is Azure limiting outgoing connections

Question

I'm running a VM in Azure on which I have a service that makes a lot of outgoing http client calls. After a while (approx 10 minutes) when the service has made around 5000-10000 calls it suddenly starts to get Connection Refused as reponse to the requests.

When running the same service locally (tried in many environments and computers) it runs without any error. We are using the HttpClient class for the request. The requests are done in 3 tasks running concurrently.

Is there some limits on the amount of outgoing connections in Azure that I should be aware of?

Answer 1

There is a maximum connection limit per azure subscription.

You should reuse the connections instead of opening new ones.

Read more about it here: http://www.freekpaans.nl/2015/08/starving-outgoing-connections-on-windows-azure-web-sites/

Answer 2

We have hit similar issues in the past, and looks like the VMs have an outbound connection limit of 1024 to an external IP. Internal Azure IPs, when they are in the same data center won't have this limitation since internal routing tables are able to handle those connections.

There is a lot of relevant information here: https://docs.microsoft.com/en-us/azure/load-balancer/load-balancer-outbound-connections#snatexhaust

Summarizing key points:

1. Try assigning a public IP to your VM if it doesn't have one. This is only viable if you are running a handful of VMs.
2. Try adding multiple IPs to your VNET/Load balancer if you are running behind one. Each external IP will multiply your connection limit.
3. Try optimizing your connection usage, i.e. keep connections alive for longer for efficient pipe-lining.