You now have a queuing system that works and generates pdfs which are sent to users as per RabbitMQ and PHP Part 1 of this article. A week later after launching the queuing system you get one or two queries from users who claim to have made a request to get the pdf report but it never arrived. Okay, what could have happened ? well you go through the application log files and as suspected - An Exception was thrown by one your classes as the consumer was trying to create the pdf and that is why it was never sent. Now this compromises the queuing system Totally, But wait there is a way to help prevent such.

He shows how to make your queues "durable", meaning they'll survive a broker restart and they require a response from the consumer before being removed. He shows how (via the php-ampq functionality) to add the "AMPQ_DURABLE" flag to the queue definition. He also includes some code showing how to send back the acknowledgement so the entry can be removed from the queue. He also includes an update to the code that calls "publish" to make the messages persistent too.

There are times when you have to make certain features of your PHP application to work asynchronously, and there are times when you do not have to - I will explain this better by introducing every day scenarios.

His two scenarios have a common thread - the need for asynchronous processing, especially for something that can scale as the user base grows. With the help of RabbitMQ he shows you how to install the MW server, get the php-ampq extension for PHP installed and two sample scripts - one to send a message to the broker, the other to receive and parse the result of a job.