Akka Cluster, Cluster Sharding and Cluster singleton use cases
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20-12-2019 - |
Question
I am writing an Akka application and I want to use the Akka Cluster feature that Typsafe provides. I am trying to understand the main difference between Akka Cluster, Akka Cluster Singleton and Akka Cluster Sharding. To me, they seem to be providing similar things.
In my scenario I want to have a cluster that will have:
- Stateless actors that could live in any machine (I will have a pool of them)
- Stateless actors that I want them to live in specific machines
- Stateful actors that could live in any machine but I need just one instance of them across the whole cluster and being able to restart the actor with its previous state if it dies.
Based on what I have read I would need Akka Cluster for the first kind, Akka Cluster Singleton for the second kind and Akka Cluster Sharding for the third kind. Is my assumption correct? I am looking for some guidance as well as any example online if you know any.
Solution
"Stateless actors that could live in any machine" -- this sounds like akka cluster.
"Stateless actors that I want them to live in specific machines" -- this sounds like akka cluster singleton, but you can also use roles
"being able to restart the actor with its previous state if it dies" -- this sounds like Akka Cluster Sharding with akka-persistence.
OTHER TIPS
Take a look at https://github.com/dnvriend/spray-ba-sharding and https://github.com/dnvriend/spray-ba-singleton for some use case. The akka documentation is actually pretty good. Also look at the activator templates.