Add .NET Kafka webserver

[RayCoulstock]

Motivation

• Provide a simple ASP.NET Core webserver option so C# students can interact with Kafka from a familiar stack.
• Keep the server intentionally minimal with one page to send keyed string messages and one page to view recently consumed messages so it can be edited during class.
• Make the service runnable in the existing course environment via Docker Compose and a dedicated topic to avoid interfering with existing examples.

Description

• Add a minimal ASP.NET Core app (webserver-dotnet/Program.cs) exposing /produce to send messages and /consume to view recent messages, using Confluent.Kafka for production and a background consumer.
• Add a .NET project file (webserver-dotnet/webserver-dotnet.csproj) and a Dockerfile (webserver-dotnet/Dockerfile) for containerized runs, plus .dockerignore.
• Register a webserver-dotnet service in docker-compose.yml (mapped to host port 3005) and add creation of the dotnet-messages topic to the create-topics service.
• Update README.md with instructions on how to start the .NET webserver and where to access the produce and consume pages.

Testing

• Ran git diff --check to validate there are no trivial whitespace or diff errors and it completed successfully.
• Parsed docker-compose.yml with a small YAML check (ruby -e 'require "yaml"; ...') to confirm the webserver-dotnet service and its port are present and the check succeeded.
• Attempted to run the ./dotnet-install.sh and dotnet build steps but they could not complete because the environment lacked a local .NET SDK and the installer was blocked by the network/proxy, so the build could not be verified here.
• Attempted to run docker compose config / docker-compose config to validate the Compose file but this environment does not have Docker installed, so compose validation could not be performed here.

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[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Wait for topic creation before starting the .NET server

In the documented docker-compose up -d zookeeper kafka create-topics webserver-dotnet flow, this short-form depends_on only orders container startup; Docker's startup-order docs state it does not wait for a dependency to be ready or for a one-shot job to complete. Because Kafka has auto topic creation disabled and dotnet-messages is created later by create-topics, the .NET consumer/producer can start against a missing topic and fail or return produce errors on a fresh environment, unlike the existing webservers that explicitly wait for their topic/schema before running.

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