Scalability: using a pool of servers to receive, process and send message

I have a scenario where background service need to receive message, process the request and send back message to the requested client. I'd like to use a pool of servers for scalability. What is the architectural guidance to make sure that a message is processed only by one server in the pool?

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* ID: 1bbb2d1c-4dfe-3faf-d4b0-65ae1146961e
* Version Independent ID: 6b203f18-adfa-3a18-183d-b124325064c3
* Content: [Host ASP.NET Core SignalR in background services](https://docs.microsoft.com/en-us/aspnet/core/signalr/background-services?view=aspnetcore-2.2)
* Content Source: [aspnetcore/signalr/background-services.md](https://github.com/aspnet/AspNetCore.Docs/blob/master/aspnetcore/signalr/background-services.md)
* Product: **aspnet-core**
* Technology: **aspnetcore-signalr**
* GitHub Login: @bradygaster
* Microsoft Alias: **bradyg**