Control plane

Store

BigConfig Store is a library for implementing the desired state of a control plane with an audit log. It uses Redis Sorted Sets to store the events and the snapshots.

Usage

• Get enough RAM to hold all your data.
• Implement the business logic of the control plane as a PURE event-handling function.
• Keep the control loop separate from the event-handling function.
• All events need to be replayable and produce the same state.

1. Start Redis in a shell

   redis-server

2. Require the store library

   (ns my-control-plane
     (:require
      [big-config.store :refer [store! handle!]]))

3. The pure business logic

   ; Your business logic as a pure function. Returns the new state with event applied.
   (defn my-business [state event timestamp]
     (case event
       :reset {:counter 0}
       :inc (update state :counter inc)))

4. Increment the counter two times

   (with-open [p1 (store! {:business-fn my-business
                           :wcar-opts {:pool :none}})]
     ; The default initial state is an empty map.
     ; :reset will set the state to {:counter 0}
     (handle! p1 :reset)
     (assert (= @p1 {:counter 0}))
     ; Your events can be any Clojure value or Serializable object.
     (handle! p1 :inc)
     (handle! p1 :inc)
     ; Your system state with the events applied.
     (assert (= @p1 {:counter 2}))
     @p1)

5. Read the counter again

   (with-open [p2 (store! {:business-fn my-business
                           :wcar-opts {:pool :none}})]
     ; the state is recovered, even if there was a system crash.
     (assert (= @p2 {:counter 2}))
     @p2)

Shortcomings

• RAM: It requires enough RAM to hold all the data in your business state.
• Start-up time: The entire state is read into RAM.

Credit

BigConfig Store is a reimplementation of prevayler-clj in Redis.

Use case Control plane

Blog article Demystifying the control plane: the easy upgrade path from GitOps with BigConfig