Error when doing request from Event Handler

Question

In our SDL Web 8.5 environment we have an Event Handler, which does a POST request to a .NET Core API (hosted on another server).

The request results in the following error:

One or more errors occurred. An error occurred while sending the request. The underlying connection was closed: An unexpected error occurred on a send. Unable to read data from the transport connection: An existing connection was forcibly closed by the remote host. An existing connection was forcibly closed by the remote host

Component: Tridion.ContentManager Errorcode: 0 User: NT AUTHORITY\SYSTEM

The interesting thing is that when I do the same request via Postman from the same server, the requests succeeds.

My code in the Event Handler looks like this:

var client = new HttpClient
{
    BaseAddress = new Uri(endPoint),
    Timeout = new TimeSpan(0, 0, 20)
};

var x = client.PostAsync($"/api/{rootElementName}", content).Result;

Another interesting detail is that this does work on our development server.

Answer 1

These servers have restricted which TLS version can be used. Adding the following line of code fixed the issue:

System.Net.ServicePointManager.SecurityProtocol |= SecurityProtocolType.Tls11 | SecurityProtocolType.Tls12;