Skip to main content

RabbitMQ–Using Alternate Exchanges to avoid loosing messages

A few days ago I blogged about a situation we had where some messages send to RabbitMQ got lost. I showed a possible solution when using MassTransit. We further investigated the issue and a colleague(thanks Stijn!) suggested another solution by using a specific RabbitMQ feature: Alternate Exchanges.

The documentation explains the feature like this:

It is sometimes desirable to let clients handle messages that an exchange was unable to route (i.e. either because there were no bound queues or no matching bindings). Typical examples of this are

  • detecting when clients accidentally or maliciously publish messages that cannot be routed
  • "or else" routing semantics where some messages are handled specially and the rest by a generic handler

Alternate Exchange ("AE") is a feature that addresses these use cases.

Whenever an exchange with a configured AE cannot route a message to any queue, it publishes the message to the specified AE instead. If that AE does not exist then a warning is logged. If an AE cannot route a message, it in turn publishes the message to its AE, if it has one configured. This process continues until either the message is successfully routed, the end of the chain of AEs is reached, or an AE is encountered which has already attempted to route the message.

That is exactly the kind of problem we had, so Alternate Exchanges sounds like the perfect solution for us.

You can specify an alternate exchange through the MassTransit configuration:

However the recommended way to configure this is through RabbitMQ policies. When using a policy we specify a pattern(through a regex) to define when the policy should apply and the exact rules of the policy.

Policies can be created directly from the commandline:

rabbitmqctl set_policy AE "^my-direct$" '{"alternate-exchange":"my-ae"}' --apply-to exchanges

Or through the Management plugin:

  • Go to the Management UI of your RabbitMQ cluster
  • Click on Policies on the right

  • Go to the Add / update a policy section. Specify a name, a regex pattern, the scope it should apply to and add one or more definitions. In our case we choose the Alternate exchange and specify the name of our exchange.
  • Click on Add / update policy to save the policy.
  • Now for every exchange that is created that matches the pattern an alternate-exchange is automatically configured.

That’s it!

More information

Parameters and Policies — RabbitMQ

Alternate Exchanges — RabbitMQ

Popular posts from this blog

.NET 8–Keyed/Named Services

A feature that a lot of IoC container libraries support but that was missing in the default DI container provided by Microsoft is the support for Keyed or Named Services. This feature allows you to register the same type multiple times using different names, allowing you to resolve a specific instance based on the circumstances. Although there is some controversy if supporting this feature is a good idea or not, it certainly can be handy. To support this feature a new interface IKeyedServiceProvider got introduced in .NET 8 providing 2 new methods on our ServiceProvider instance: object? GetKeyedService(Type serviceType, object? serviceKey); object GetRequiredKeyedService(Type serviceType, object? serviceKey); To use it, we need to register our service using one of the new extension methods: Resolving the service can be done either through the FromKeyedServices attribute: or by injecting the IKeyedServiceProvider interface and calling the GetRequiredKeyedServic...

Azure DevOps/ GitHub emoji

I’m really bad at remembering emoji’s. So here is cheat sheet with all emoji’s that can be used in tools that support the github emoji markdown markup: All credits go to rcaviers who created this list.

Kubernetes–Limit your environmental impact

Reducing the carbon footprint and CO2 emission of our (cloud) workloads, is a responsibility of all of us. If you are running a Kubernetes cluster, have a look at Kube-Green . kube-green is a simple Kubernetes operator that automatically shuts down (some of) your pods when you don't need them. A single pod produces about 11 Kg CO2eq per year( here the calculation). Reason enough to give it a try! Installing kube-green in your cluster The easiest way to install the operator in your cluster is through kubectl. We first need to install a cert-manager: kubectl apply -f https://github.com/cert-manager/cert-manager/releases/download/v1.14.5/cert-manager.yaml Remark: Wait a minute before you continue as it can take some time before the cert-manager is up & running inside your cluster. Now we can install the kube-green operator: kubectl apply -f https://github.com/kube-green/kube-green/releases/latest/download/kube-green.yaml Now in the namespace where we want t...