The eventhistory consumes all events from the configured event system like NATS, stores them and allows other services to retrieve them via an eventid.

Prerequisites

Running the eventhistory service without an event sytem like NATS is not possible.

Consuming

The eventhistory services consumes all events from the configured event sytem.

Storing

The eventhistory service stores each consumed event via the configured store in EVENTHISTORY_STORE_TYPE. Possible stores are:

mem: Basic in-memory store and the default.
ocmem: Advanced in-memory store allowing max size.
redis: Stores data in a configured redis cluster.
etcd: Stores data in a configured etcd cluster.
nats-js: Stores data using key-value-store feature of nats jetstream
noop: Stores nothing. Useful for testing. Not recommended in productive enviroments.

Note that in-memory stores are by nature not reboot persistent.
Though usually not necessary, a database name and a database table can be configured for event stores if the event store supports this. Generally not applicapable for stores of type in-memory. These settings are blank by default which means that the standard settings of the configured store applies.
Events stay in the store for 2 weeks by default. Use EVENTHISTORY_RECORD_EXPIRY to adjust this value.
The eventhistory service can be scaled if not using in-memory stores and the stores are configured identically over all instances.

Retrieving

Other services can call the eventhistory service via a grpc call to retrieve events. The request must contain the eventid that should be retrieved.