Configuration Management and Operational Rigor Questions

package main

import (
	"context"
	"errors"
	"log"
	"sync"
	"time"
)

type Key string

// simplified metrics
var (
	reconcileSuccess = NewCounter()
	reconcileFailure = NewCounter()
)

// --- pseudo implementations ---
func isLeader(ctx context.Context) bool { return true } // replace with lease/lock
func readDesired(ctx context.Context) map[Key]string { return map[Key]string{} }
func readNodeState(ctx context.Context) map[Key]string { return map[Key]string{} }
func applyChange(ctx context.Context, k Key, desired string) error { return nil }
func isTransient(err error) bool { return true }

// --- counters
type Counter struct{ mu sync.Mutex; v int }
func NewCounter() *Counter { return &Counter{} }
func (c *Counter) Inc() { c.mu.Lock(); c.v++; c.mu.Unlock() }

func main() {
	ctx := context.Background()
	// work queue with dedupe and condition variable
	type queue struct {
		mu      sync.Mutex
		items   []Key
		inQueue map[Key]bool
		cond    *sync.Cond
	}
	q := &queue{inQueue: map[Key]bool{}}
	q.cond = sync.NewCond(&q.mu)

	// start workers
	workers := 5
	var wg sync.WaitGroup
	for i := 0; i < workers; i++ {
		wg.Add(1)
		go func(id int) {
			defer wg.Done()
			for {
				q.mu.Lock()
				for len(q.items) == 0 {
					q.cond.Wait()
				}
				k := q.items[0]
				q.items = q.items[1:]
				delete(q.inQueue, k) // allow re-queue after pop
				q.mu.Unlock()

				// process with retries
				var attempt int
				for {
					attempt++
					desired := "" // fetch desired per key or pass payload
					err := applyChange(ctx, k, desired)
					if err == nil {
						reconcileSuccess.Inc()
						break
					}
					reconcileFailure.Inc()
					if !isTransient(err) || attempt >= 5 {
						log.Printf("permanent failure for %s: %v", k, err)
						break
					}
					backoff := time.Duration(100*(1<<attempt)) * time.Millisecond
					time.Sleep(backoff)
				}
			}
		}(i)
	}

	// reconciliation loop (leader only)
	ticker := time.NewTicker(15 * time.Second)
	for range ticker.C {
		if !isLeader(ctx) { continue }
		desired := readDesired(ctx)
		node := readNodeState(ctx)
		// diff and enqueue
		for k, want := range desired {
			if nodeVal, ok := node[k]; !ok || nodeVal != want {
				q.mu.Lock()
				if !q.inQueue[k] {
					q.items = append(q.items, k)
					q.inQueue[k] = true
					q.cond.Signal()
				}
				q.mu.Unlock()
			}
		}
	}
}

import time
import random

class NonRetriableError(Exception):
    pass

class TransientError(Exception):
    pass

def safe_apply(change_func, dry_run_func, apply_func, max_retries=5, base_delay=1.0, validate=None):
    """
    Attempts a dry-run, validates it, then applies the change with retries/backoff.
    - change_func: description or callable producing change metadata (optional)
    - dry_run_func: callable() -> result (should not mutate)
    - apply_func: callable() -> result (performs change)
    - max_retries: int
    - validate: callable(dry_run_result) -> bool (if None, truthiness used)
    Returns dict: {status: 'success'|'failed'|'skipped', reason: str, attempts: int}
    """
    # Dry-run
    try:
        dry_result = dry_run_func()
    except NonRetriableError as e:
        return {"status":"failed","reason":f"dry-run non-retriable: {e}","attempts":0}
    except Exception as e:
        return {"status":"failed","reason":f"dry-run error: {e}","attempts":0}

    if validate:
        ok = False
        try:
            ok = bool(validate(dry_result))
        except Exception as e:
            return {"status":"failed","reason":f"validation error: {e}","attempts":0}
        if not ok:
            return {"status":"skipped","reason":"dry-run validation failed","attempts":0}

    # Apply with retries + exponential backoff
    attempt = 0
    while attempt < max_retries:
        attempt += 1
        try:
            res = apply_func()
            return {"status":"success","reason":"applied","attempts":attempt,"result":res}
        except NonRetriableError as e:
            return {"status":"failed","reason":f"apply non-retriable: {e}","attempts":attempt}
        except TransientError as e:
            if attempt >= max_retries:
                return {"status":"failed","reason":f"transient failures exhausted: {e}","attempts":attempt}
            # jittered exponential backoff
            sleep = base_delay * (2 ** (attempt - 1))
            sleep *= random.uniform(0.8, 1.2)
            time.sleep(sleep)
        except Exception as e:
            # treat unknown exceptions as non-retriable by default
            return {"status":"failed","reason":f"unexpected error: {e}","attempts":attempt}
    return {"status":"failed","reason":"max retries reached","attempts":attempt}