Here's an example:
TYPE : TOPIC
exchange.v1 -> queue.order
exchange.v2 -> queue.log
so when the apps running it's must configure the exchange first right? and in a single service only can have 1 exchange?
I have 1 service for logging and 1 service for ordering. all proses will be sent into logging service and then forward another event. in this case to queue.order
So it's possible to publish an event from a different exchange? or I miss something? please let me know :(
Exchanges are not tied to “services”, much less in a 1:1 manner.
Exchanges in RabbitMQ are message sinks. Any existing exchanges can be published to by any number of applications (“services”) with adequate permissions.
Exhanges can either be pre-deployed or created automatically by an application. Pre-deployment is usually more common. This may or may not be outside the lifecycle of a single “service”.
Exchanges (depending on type) may also route to any number of queues on the same vhost.
Now, with all of that out of the way..
It is very possible to forward a message from a queue to another exchange: read from queues (stores), publish to exchanges (sinks). This can be done in code or even from a tool like the Shovel plugin - the “correct” approach depends significantly based on semantics, just as the choice of routing.
Personally, I recommend keeping RabbitMQ processing chains to as limited a scope as allowed by the application domain.
Related
Let's consider a system where thousands of clients data is published to a RabbitMQ exchange (client_id is known at this stage). Exchange routes them to a single queue. Finally, messages are consumed by a single application. Works great.
However, over time, the consuming application becomes a bottleneck and needs to be scaled horizontally. The problem is the system requires that messages considering particular client are consumed by the same instance of the application.
I can create lots of queues: either one per client or use a topic exchange and route it based on some client_id prefix. Still, I don't see an elegant way how to design the consumer application so that it can be scaled horizontally (as it requires stating queues that it consumes explicitly).
I'm looking for RabbitMQ way for solving this problem.
RabbitMQ has x-consistent-hash and x-modulus-hash exchanges that can be used to solve the problem. When these exchanges are used, messages get partitioned to different queues according to hash values of routing keys. Of course, there are differences between x-consistent-hash and x-modulus-hash in the way how partitioning is implemented, but main idea stays the same - messages with the same routing key (client_id) will be distributed to the same queue and eventually should be consumed by the same application.
For example, the system can have the following topology: every application can define an exclusive queue (used by only one connection and the queue will be deleted when that connection closes) that is binded to the exchange (x-consistent-hash or x-modulus-hash).
In my opinion, it is a good idea to have a distributed cache layer in this particular scenario, but RabbitMQ provides the plugins to tackle this kind of problems.
I'm working with a product suite which uses RabbitMQ as a back end for service bus messaging. Many of the clients use software (NeuronESB) which is supposed to automatically configure exchanges, queues and channels as needed. Somewhere in the system exchanges in Rabbit are being deleted and not re-created, resulting in unexpected issues. Because of the size of the system and closed source nature of at least one of the service bus clients, an audit of code has been unsuccessful in determining the source of the deletion of these exchanges.
I have tried using the firehose functionality of Rabbit, but that only provides the messages being sent through Rabbit, not the internal activities I need.
What methods are available for logging the creation and deletion of exchanges in RabbitMQ? Ideally I would like to know the date, time and client IP of the deleter, but even just getting the date and time would allow me to narrow my search of logs to help find the offender.
Try Events Exchange plugin that should do the trick.
If not working for some reason, the last resort I can think of:
Get a test environment with less clients/messages if you app is busy, then analyse your traffic with wireshark (it can understand amqp) to filter out requests to delete exchange.
We have multiple web and windows applications which were deployed to different servers that we are planning to integrate using NservierBus to let all apps can pub/sub message between them, I think we using pub/sub pattern and using MSMQ transport will be good for it. but one thing I am not clear if it is a way to avoid hard code to set sub endpoint to MSMQ QueueName#ServerName which has server name in it directly if pub is on another server. on 6-pre I saw idea to set endpoint name then using routing to delegate to transport-level address, is that a solution to do that? or only gateway is the solution? is a broker a good idea? what is the best practice for this scenario?
When using pub/sub, the subscriber currently needs to know the location of the queue of the publisher. The subscriber then sends a subscription-message to that queue, every single time it starts up. It cannot know if it subscribed already and if it subscribed for all the messages, since you might have added/configured some new ones.
The publisher reads these subscriptions messages and stores the subscription in storage. NServiceBus does this for you, so there's no need to write code for this. The only thing you need is configuration in the subscriber as to where the (queue of the) publisher is.
I wrote a tutorial myself which you can find here : http://dennis.bloggingabout.net/2015/10/28/nservicebus-publish-subscribe-tutorial/
That being said, you should take special care related to issues regarding websites that publish messages. More information on that can be found here : http://docs.particular.net/nservicebus/hosting/publishing-from-web-applications
In a scale out situation with MSMQ, you can also use the distributor : http://docs.particular.net/nservicebus/scalability-and-ha/distributor/
As a final note: It depends on the situation, but I would not worry too much about knowing locations of endpoints (or their queues). I would most likely not use pub/sub just for this 'technical issue'. But again, it completely depends on the situation. I can understand that rich-clients which spawn randomly might want this. But there are other solutions as well, with a more centralized storage and an API that is accessed by all the rich clients.
I'm in the process of implementing various remote methods/RPCs on the top of AMQP (RabbitMQ in particular). When a worker (or a client) comes online, it could, in theory, declare (create) a queue on the exchange. The other approach is to just start using a queue and assume that it already exists on the exchange.
Which approach is more common? Creating queues manually has a higher administrative cost, maybe; however, it can result in a more consistent environment if we decouple queue management from queue usage.
It depends what is the requirement. If you have a fixed number of queues and dont need it to be generated dynamically, then go for manual. Example : It is a integration application and I know I have 3 consumers A,B,C then I will manually create 3 queues. Another example in a chat application for every logged in user I want to create a queue, in that case queues should be created programatically. And in case manual creation, you have more control to implement permissions and ACLs.
Meanwhile I found out that according to RabbitMQ applications should take care of managing the queues they use.
I have to implement this scenario:
An external application publish message to rabbitmq.
This message has a client_id property. We can place this id to routing key or message header or some other property.
I have to implement sharding in a exchange routng logic - the message should be delivered to specific queue based on the client_id range.
Is it possible to implement in a standard exchanges?
If not what exchange should I take as the base?
How to dynamicly change client_id ranges?
Take a look at the rabbitmq plugin. It's included in the RabbitMQ distribution from v3.6.0 onwards.
Just have your producer put enough info into the routing key that causes the message to go into the right queue on the other side of the Exchange.
So for example, create two queues called 1 and 2 and bind them with routing keys matching the names. Then have your producer decide which routing key to use when producing the event message. Customers with names starting with letters a-m go to 1, n-z go to 2, you get the idea. It pushes the sharding to the producer but that might be OK for your application.
AMQP doesn't have any explicit implementation of sharding, but its architecture should help you to do that.
Spreading messages to several queues is just a rabbitmq challenge (and part of amqp specification), and with routing, way you can attach hetereogeneous consumers to handle specific messages routed via the same exchange. Therefore, producer should push a specific key to be consumed by specific queue/consumer...
You can decide to make a static sharding, perhaps you have 10 queues with one consumer per queue. You could implement a consistent hashing function such that key is CLIENT_ID % 10.
Another ways and none static solutions could be propoused, and you can try to over this architecture.