Which part of Orleans is actually distributed?

Question

There is a couple of confusing points in the documentation that make me struggle to understand how exactly distribution across the cluster happens in Orleans. Hence, the questions.

Question #1

Orleans claims to have a built-in distribution capabilities to distribute across multiple servers. To me it sounds that Orleans can act as a load balancer itself and can scale out automatically. Thus, if I deploy Orleans app to several servers, then service discovery and load management should happen automatically, correct?

In this case, why some docs and articles suggest using other tools, like Ocelot or Consul, as a single entry point to Orleans cluster?

Question #2

I would like to use simple but distributed in-memory storage across several servers, like Redis or Apache Ignite, and I would like to know if it's possible to use a simple grain as this kind of a data storage?

Let's say, one grain will store a collection of restaurants and some other grain will keep track of the last 1000 visitors for selected restaurant. Can I activate these 2 grains only once as a singleton collection, add or remove records to each collection, and use these 2 grains as in-memory storage evenly available to all nodes in the cluster? Also, if answer is yes, do I need to add locks to these collections or each grain always exists in a single thread?

Answer 1

1. Service discovery and load management happen automatically indeed. Consul is not a strong required. The only external requirement is a Membership table provider - something that is used internally by Orleans Clustering. There are many build in Membership table providers that come already built-in with Orleans. For example, Azure table storage. all you need is to configure Orleans to use it and of course have Azure storage account. Consul is another alternative to Membership table provider and there are more.

Another thing that does not come built-in is infrastructure scaling. If your service demand increases, something need to ask the infrastructure provider (Cloud Provider) to add more Servers. Once servers are added, Orleans will automatically adjust the workload and load balance across the new servers as well. But figuring out that more servers are needed and adding them is not done by Orleans itself (there likely some externally contributed tools to do that. maybe K8 can be configured to do that? I am not completely sure about that).

2. Yes, you can use those 2 grains as in-memory storage, just like you wrote. And no, you do not need to use locks. All grains are single threaded.