Storage

Storage of projected read models / documents and events are configured through the Cratis Kernel. The reason for this is that projections typically share the storage of what the queries in a client is built on. To avoid configuring things in multiple places, we have it in the Kernel and the client will get this configuration upon startup.

Within the cratis.json file you should have a storage key and object to hold its configuration:

{
    "storage": {}
}

The storage object is expecting the following shape:

{
    "storage": {
        "cluster": {                                            // Configuration for the shared database for the entire Cratis cluster
            "type": "MongoDB",
            "connectionDetails": "mongodb://localhost:27017/cratis-shared"
        },
        "microservices": {                                      // Configuration per microservice
            "00000000-0000-0000-0000-000000000000": {           // Microservice Id
                "shared": {                                     // Data that is shared between all the tenants
                    "eventStore": {
                        "type": "MongoDB",
                        "connectionDetails": "mongodb://localhost:27017/event-store-shared"
                    }
                },
                "tenants": {                                    // Tenant specific configuration
                    "3352d47d-c154-4457-b3fb-8a2efb725113": {   // Tenant identifier of the tenant
                        "readModels": {                         // Read models
                            "type": "MongoDB",
                            "connectionDetails": "mongodb://localhost:27017/dev-read-models"
                        },
                        "eventStore": {                         // Event Store
                            "type": "MongoDB",
                            "connectionDetails": "mongodb://localhost:27017/dev-event-store"
                        }
                    }
                }
            }
        }
    }
}

The kernel recognizes 2 types of storage types; readModels and eventStore.

Cluster level

The Cratis cluster has data that is shared across all microservices and across all tenants. This is stored in the cluster database that is first configured.

Microservices

Every microservice would have a key within the microservices key of the storage object. If you only have one microservice, you still need this. The default for a single microservice or monolith would be 00000000-0000-0000-0000-000000000000.

Shared

Cratis has information that is shared across all tenants. This is the shared configuration within a microservice.

Tenancy

A microservice must have at least one tenant, even if your software is a single tenant environment. The tenants part of the configuration configures all your tenants.

Type

Within each storage configuration there is a type property that is required. This property specifies which storage technology to use.

Note: As of January 2022 - MongoDB is the only supported type. The Kernel has been designed to support others, and could do so if there is enough interest for it.

For MongoDB the value would be a valid MongoDB connection string, fully qualified with the database name at the end.