One question I’ve been asked quite a lot, is ‘why?’. Why am I building a .NET API when one is already available; the C# AMQP client from RabbitHQ? Think of AMQP as the HTTP of messaging. It’s a relatively low-level protocol. You typically wouldn’t build a web application directly against a low-level HTTP API such as System.Net.WebRequest, instead you would use a higher level toolkit such as WCF or ASP.NET MVC. Think of EasyNetQ as the ASP.NET MVC of AMQP.
AMQP is designed to be cross platform and language agnostic. It is also designed to flexibly support a wide range of messaging patterns based on the Exchange/Binding/Queue model. It’s great having this flexibility, but with flexibility comes complexity. It means that you will need to write a significant amount of code in order to implement a RabbitMQ client. Typically this code would include:
- Implementing messaging patterns such as Publish/Subscribe or Request/Response. Although, to be fair, the .NET client does provide some support here.
- Implement a routing strategy. How will you design your exchange-queue bindings, and how will you route messages between producers and consumers?
- Implement message serialization/deserialization. How will you convert the binary representation of messages in AMQP to something your programming language understands?
- Implement a consumer thread for subscriptions. You will need to have a dedicated consumer loop waiting for messages you have subscribed to. How will you deal with multiple subscribers, or transient subscribers, like those waiting for responses from a request?
- Implement a versioning strategy for your messages. What happens when your message schema needs to change in response to business requirements?
- Implement subscriber reconnection. If the connection is disrupted or the RabbitMQ server bounces, how do you detect it and make sure all your subscriptions are rebuilt?
- Understand and implement quality of service settings. What settings do you need to make to ensure that you have a reliable client.
- Implement an error handling strategy. What should your client do if it receives a malformed message, or if an unexpected exception is thrown?
- Implement monitoring tools. How will you monitor your client applications so that you are alerted if there are any problems?