040 Project 40: Infra Reconciler Daemon

040 Build an Infra Reconciler Daemon

Model a control-loop daemon that continuously moves actual state toward desired state.

desired config -> diff -> apply actions -> observe -> repeat

Full main.go

package main

import (
    "fmt"
    "time"
)

type state struct {
    Desired int
    Actual  int
}

func diff(s state) int { return s.Desired - s.Actual }

func apply(s *state) string {
    d := diff(*s)
    switch {
    case d > 0:
        s.Actual++
        return "scale_up"
    case d < 0:
        s.Actual--
        return "scale_down"
    default:
        return "noop"
    }
}

func main() {
    s := state{Desired: 5, Actual: 1}
    tick := time.NewTicker(400 * time.Millisecond)
    defer tick.Stop()

    for i := 0; i < 20; i++ {
        <-tick.C
        action := apply(&s)
        fmt.Printf("tick=%02d desired=%d actual=%d action=%s\n", i, s.Desired, s.Actual, action)
        if i == 10 {
            s.Desired = 3
        }
    }
}

Step-by-Step Explanation

  1. Model desired and actual state explicitly.
  2. Compute a minimal diff.
  3. Apply one idempotent reconciliation step.
  4. Observe updated state and repeat.
  5. Keep loops convergent and failure-aware.

Code Anatomy

  • State model captures control-plane truth.
  • Reconcile function decides next action.
  • Loop executes continuously with visibility into actions.

Learning Goals

  • Learn the controller pattern used in modern platforms.
  • Build robust automation through repeated reconciliation.
  • Understand convergence over one-shot scripting.