events
Introduction
Event vs Log
Events: business centric, system behaviour
Logs: more technical, operational insights
A signe business operation may generate both, event for business significance, log for technical execution.
Event sourcing
In Event Sourcing, events are central to describe intents (commands) and state changes. It should be the unique source of truth.
Current state are derived from events, as the sum of changes. Current state can be reconstructed by replaying all events from the event store.
Since deriving current state from events is computationaly expensive, states are stored in projections.
CQRS is a pedantic acronym for a simple concept: event producers and consumers should be totally independents.
pros: scalability, cheap writes, support logging/debugging
cons: complexity, eventualy consistent, async paradigm, expensive reads
Domain event
LavinMQ
install (Debian)
# cd /etc/apt/trusted.gpg.d
# curl -L https://packagecloud.io/cloudamqp/lavinmq/gpgkey > lavinmq.asc
# cd /etc/apt/sources.list.d
# echo "deb https://packagecloud.io/cloudamqp/lavinmq/debian <RELEASE> main" > lavinmq.list
# apt update
# apt install lavinmq
config