Event sourcing configuration

In this article, you learn about various event sourcing configuration options for .NET Orleans.

Configure project references

Grain interfaces

As before, interfaces depend only on the Microsoft.Orleans.Core package because the grain interface is independent of the implementation.

Grain implementations

Journaled grains need to derive from JournaledGrain<T, U> or JournaledGrain<T>, which is defined in the Microsoft.Orleans.EventSourcing package.

Log-consistency providers

We currently include three log-consistency providers (for state storage, log storage, and custom storage). All three are contained in the Microsoft.Orleans.EventSourcing package as well. Therefore, all journaled grains already have access to them. For a description of what these providers do and how they differ, see Included log-consistency providers.

Cluster configuration

Configure log-consistency providers just like any other Orleans providers. For example, to include all three providers (though you probably won’t need all three), add this to the <Globals> element of the configuration file:

<LogConsistencyProviders>
    <Provider Name="StateStorage"
        Type="Orleans.EventSourcing.StateStorage.LogConsistencyProvider" />
    <Provider Name="LogStorage"
        Type="Orleans.EventSourcing.LogStorage.LogConsistencyProvider" />
    <Provider Name="CustomStorage"
        Type="Orleans.EventSourcing.CustomStorage.LogConsistencyProvider" />
</LogConsistencyProviders>

You can achieve the same programmatically. Starting with Orleans 2.0.0 stable, ClientConfiguration and ClusterConfiguration no longer exist. They have been replaced by ClientBuilder and SiloBuilder (note there’s no cluster builder).

builder.AddLogStorageBasedLogConsistencyProvider("LogStorage")

Grain class attributes

Each journaled grain class must have a LogConsistencyProviderAttribute to specify the log-consistency provider. Some providers additionally require a StorageProviderAttribute, for example:

[StorageProvider(ProviderName = "OrleansLocalStorage")]
[LogConsistencyProvider(ProviderName = "LogStorage")]
public class EventSourcedBankAccountGrain :
    JournaledGrain<BankAccountState>, IEventSourcedBankAccountGrain
{
    //...
}

So here, "OrleansLocalStorage" is used for storing the grain state, whereas "LogStorage" is the in-memory storage provider for EventSourcing events.

LogConsistencyProvider attributes

To specify the log-consistency provider, add a [LogConsistencyProvider(ProviderName=...)] attribute to the grain class and provide the name of the provider as configured in the cluster configuration, for example:

[LogConsistencyProvider(ProviderName = "CustomStorage")]
public class ChatGrain :
    JournaledGrain<XDocument, IChatEvent>, IChatGrain, ICustomStorage
{
    // ...
}

StorageProviderAttribute attributes

Some log-consistency providers (including LogStorage and StateStorage) use a standard StorageProviderAttribute to communicate with storage. Specify this provider using a separate StorageProviderAttribute attribute, as follows:

[LogConsistencyProvider(ProviderName = "LogStorage")]
[StorageProvider(ProviderName = "AzureBlobStorage")]
public class ChatGrain :
    JournaledGrain<XDocument, IChatEvent>, IChatGrain
{
    // ...
}

Default providers

You can omit the LogConsistencyProvider and/or StorageProviderAttribute attributes if a default is specified in the configuration. Do this by using the special name Default for the respective provider. For example:

<LogConsistencyProviders>
    <Provider Name="Default"
        Type="Orleans.EventSourcing.LogStorage.LogConsistencyProvider"/>
</LogConsistencyProviders>
<StorageProviders>
    <Provider Name="Default"
        Type="Orleans.Storage.MemoryStorage" />
</StorageProviders>