dynamo-es

A DynamoDB implementation of the PersistedEventRepository trait in cqrs-es.

Usage

Add to your Cargo.toml file:

[dependencies]
cqrs-es = "0.4.11"
dynamo-es = "0.4.11"

Requires access to a Dynamo DB with existing tables. See:

• Sample database configuration
• Sample database table layout
• Use docker-compose and the ./db/create_tables.sh script to quickly setup a local database

DynamoDb caveats

AWS' DynamoDb is fast, flexible and highly available, but it does set some limitations that must be considered in the design of your application.

Maximum limit of 25 operations in any transaction

Events are inserted in a single transaction, which limits the number of events that can be handled from a single command using this repository. To operate correctly a command must not produce more than

• 25 events if using an event store without snapshots
• 24 events if using snapshots or an aggregate store

Item size limit of 400 KB

A single event should never reach this size, but a large serialized aggregate might. If this is the case for your aggregate beware of using snapshots or an aggregate store.

Maximum request size of 1 MB

This could have the same ramifications as the above for snapshots or an aggregate store. Additionally, an aggregate instance with a large number of events may reach this threshold. To prevent an error while loading or replaying events, set the streaming channel size to a value that ensures you won't exceed this threshold.

Testing

Requires access to DynamoDb with existing tables. This can be created locally using the included docker-compose.yml and database initialization script.

To prepare a local test environment (requires a local installation of Docker and AWS CLI):

docker-compose up -d
./db/create_tables.sh

Note that this crate used the AWS DynamoDb Rust SDK, which is currently in Developer Preview. This means that any bugs will be addressed but the underlying interfaces may still be changed resulting in significant changes within this crate. See the AWS SDK public roadmap for more information.

It is recommended that tables are configured to allow only transactions. See: https://docs.aws.amazon.com/amazondynamodb/latest/developerguide/transaction-apis-iam.html

Things that could be helpful:

• User guide along with an introduction to CQRS and event sourcing.
• Demo application using the warp http server.
• Change log