How to post messages to RabbitMQ from SQL Server?

Short disclaimer: I am aware of the title of the question, but based on what you wrote in the comments (as well of course in the question itself), it seems that what you need is a RabbitMQ client that is able to send and receive many messages.

You don't need to write anything, there is RabbitMQ has this already. You can find it here, it's a java client called PerfTest (in the link there are also examples, but of course run it with --help) and (as name ever so obviously suggests) it is used for performance testing. You can define number of consumers, producers, messages, size of the messages etc. I have used it and still use it occasionally and it works great. Since you are (I'm assuming) new to RabbitMQ, just be vary how you pass the amqp uri parameter (here is the spec).

You can create a SQLClr to comunicate with a RabbitMQ, like in this post.

I don't believe it's a nice solution, but it seems to work.