hello! the author here! the primary reason for going with this architecture is to make it scale well with off the shelf production ready tooling. RabbitMQ was c

hello! the author here! the primary reason for going with this architecture is to make it scale well with off the shelf production ready tooling. RabbitMQ was chosen to provide a scalable durable queue for backpressure support and load balancing across runners, error handling etc. it adds onto the infra weight a bit but seems to be a simpler choice to program against and use libraries. The reasons for XTDB are mainly 2: it provides a temporal immutable store, hence the whole state of the CI system can immutably evolve like a git repo hence the whole thing can be inspected at a previous time. Bob treats time as a first class thing and not just build logs but you should be able to see the whole cluster at a past time and debug it fully as all of the state is the DB. The second reason is like @capableweb said, it decouples storage from compute so that we can have a pluggable storage and not a central point of compute.