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Scaler refactor #3
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,147 @@ | ||
| package internal | ||
|
|
||
| import ( | ||
| "aether/shared/db" | ||
| "aether/shared/logger" | ||
| "aether/shared/protocol" | ||
| "context" | ||
| "encoding/json" | ||
| "sync" | ||
| "time" | ||
|
|
||
| "github.com/redis/go-redis/v9" | ||
| ) | ||
|
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| type Scaler struct { | ||
| redis *redis.Client | ||
| discovery *Discovery | ||
| db *db.DB | ||
| activeRequests map[string]int64 | ||
| mu sync.RWMutex | ||
| checkInterval time.Duration | ||
| threshold int | ||
| maxInstances int | ||
| } | ||
|
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| func NewScaler(redis *redis.Client, discovery *Discovery, database *db.DB, checkInterval time.Duration, threshold int, maxInstances int) *Scaler { | ||
| return &Scaler{ | ||
| redis: redis, | ||
| discovery: discovery, | ||
| db: database, | ||
| activeRequests: make(map[string]int64), | ||
| mu: sync.RWMutex{}, | ||
| checkInterval: checkInterval, | ||
| threshold: threshold, | ||
| maxInstances: maxInstances, | ||
| } | ||
| } | ||
|
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| func (s *Scaler) TrackRequest(functionID string, delta int64) { | ||
| s.mu.Lock() | ||
| defer s.mu.Unlock() | ||
|
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| s.activeRequests[functionID] += delta | ||
| if s.activeRequests[functionID] < 0 { | ||
| s.activeRequests[functionID] = 0 | ||
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|
||
| } | ||
| } | ||
|
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| func (s *Scaler) Run(ctx context.Context) { | ||
| ticker := time.NewTicker(s.checkInterval) | ||
| defer ticker.Stop() | ||
|
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| for { | ||
| select { | ||
| case <-ctx.Done(): | ||
| return | ||
| case <-ticker.C: | ||
| s.check(ctx) | ||
| } | ||
| } | ||
| } | ||
|
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| func (s *Scaler) check(ctx context.Context) { | ||
| s.mu.RLock() | ||
| snapshot := make(map[string]int64, len(s.activeRequests)) | ||
| for fnID, count := range s.activeRequests { | ||
| snapshot[fnID] = count | ||
| } | ||
| s.mu.RUnlock() | ||
|
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| var toCleanup []string | ||
|
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| for functionID, activeCount := range snapshot { | ||
| if activeCount == 0 { | ||
| toCleanup = append(toCleanup, functionID) | ||
| continue | ||
| } | ||
|
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| instances, err := s.discovery.GetInstances(ctx, functionID) | ||
| if err != nil { | ||
| logger.Error("failed to get instances", "function", functionID, "error", err) | ||
| continue | ||
| } | ||
|
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+83
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| currentCount := len(instances) | ||
|
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| // Calculate target instances: ceil(active / threshold) | ||
| targetCount := int((activeCount + int64(s.threshold) - 1) / int64(s.threshold)) | ||
|
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| // Cap target at maxInstances to prevent runaway scaling | ||
| if targetCount > s.maxInstances { | ||
| targetCount = s.maxInstances | ||
| } | ||
|
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| if targetCount > currentCount { | ||
| deficit := targetCount - currentCount | ||
| logger.Info("gateway scaling up", | ||
| "function", functionID, | ||
| "active_requests", activeCount, | ||
| "current_instances", currentCount, | ||
| "target_instances", targetCount, | ||
| "provisioning", deficit) | ||
|
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| // Push provision jobs to queue | ||
| for i := 0; i < deficit; i++ { | ||
| if err := s.pushProvisionJob(ctx, functionID); err != nil { | ||
| logger.Error("failed to push provision job", "function", functionID, "error", err) | ||
| } | ||
| } | ||
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|
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| } | ||
| } | ||
|
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| if len(toCleanup) > 0 { | ||
| s.mu.Lock() | ||
| for _, functionID := range toCleanup { | ||
| if s.activeRequests[functionID] == 0 { | ||
| delete(s.activeRequests, functionID) | ||
| } | ||
| } | ||
| s.mu.Unlock() | ||
| } | ||
| } | ||
|
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| func (s *Scaler) pushProvisionJob(ctx context.Context, functionID string) error { | ||
| fn, err := s.db.GetFunction(functionID) | ||
| if err != nil { | ||
| return err | ||
| } | ||
|
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| job := protocol.Job{ | ||
| FunctionID: functionID, | ||
| ImageID: fn.CodePath, | ||
| Runtime: fn.Runtime, | ||
| Entrypoint: fn.Entrypoint, | ||
| VCPU: int(fn.VCPU), | ||
| MemoryMB: int(fn.MemoryMB), | ||
| Port: fn.Port, | ||
| EnvVars: fn.EnvVars, | ||
| } | ||
|
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| data, err := json.Marshal(job) | ||
| if err != nil { | ||
| return err | ||
| } | ||
|
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| return s.redis.LPush(ctx, "queue:vm_provision", string(data)).Err() | ||
| } | ||
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The documentation states that workers check capacity "independently (no coordination)" and that "each worker checks capacity independently", but the actual capacity check has a TOCTOU race condition. Between checking capacity (line 101-106) and spawning instances (line 188 in handleJob), multiple workers could exceed the limit. This discrepancy between the documented behavior and actual implementation could mislead users about the system's reliability.
Consider either: (1) updating the documentation to mention this race condition and its implications, or (2) implementing proper coordination to ensure the documented behavior is accurate.