golint-sl

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sideeffects

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Uses SSA analysis to detect side effects in reconcilers.

Category

Kubernetes

What It Checks

This analyzer uses Static Single Assignment (SSA) form to detect side effects that could break reconciler idempotency.

Why It Matters

Reconcilers must be idempotent - running twice should produce the same result. Side effects can break this:

  • Sending webhooks multiple times
  • Incrementing counters
  • Creating duplicate external resources

Examples

Bad: Non-idempotent Side Effect

func (r *Reconciler) Reconcile(ctx context.Context, req ctrl.Request) (ctrl.Result, error) {
    obj := &myv1.MyResource{}
    if err := r.Get(ctx, req.NamespacedName, obj); err != nil {
        return ctrl.Result{}, client.IgnoreNotFound(err)
    }

    // This runs on every reconcile!
    if err := r.sendWebhook(obj); err != nil {
        return ctrl.Result{}, err
    }

    return ctrl.Result{}, nil
}

Good: Track Side Effect State

func (r *Reconciler) Reconcile(ctx context.Context, req ctrl.Request) (ctrl.Result, error) {
    obj := &myv1.MyResource{}
    if err := r.Get(ctx, req.NamespacedName, obj); err != nil {
        return ctrl.Result{}, client.IgnoreNotFound(err)
    }

    // Check if already done
    if !obj.Status.WebhookSent {
        if err := r.sendWebhook(obj); err != nil {
            return ctrl.Result{}, err
        }
        obj.Status.WebhookSent = true
        if err := r.Status().Update(ctx, obj); err != nil {
            return ctrl.Result{}, err
        }
    }

    return ctrl.Result{}, nil
}

Good: Use Finalizers for Cleanup

func (r *Reconciler) Reconcile(ctx context.Context, req ctrl.Request) (ctrl.Result, error) {
    obj := &myv1.MyResource{}
    if err := r.Get(ctx, req.NamespacedName, obj); err != nil {
        return ctrl.Result{}, client.IgnoreNotFound(err)
    }

    // Handle deletion
    if !obj.DeletionTimestamp.IsZero() {
        if controllerutil.ContainsFinalizer(obj, finalizerName) {
            // Cleanup side effect - runs once during deletion
            if err := r.cleanup(ctx, obj); err != nil {
                return ctrl.Result{}, err
            }
            controllerutil.RemoveFinalizer(obj, finalizerName)
            return ctrl.Result{}, r.Update(ctx, obj)
        }
        return ctrl.Result{}, nil
    }

    // Add finalizer
    if !controllerutil.ContainsFinalizer(obj, finalizerName) {
        controllerutil.AddFinalizer(obj, finalizerName)
        return ctrl.Result{}, r.Update(ctx, obj)
    }

    return r.reconcile(ctx, obj)
}

Configuration

# .golint-sl.yaml
analyzers:
  sideeffects: true  # enabled by default

When to Disable

  • Non-Kubernetes projects
  • Performance-critical code (SSA analysis has overhead)
analyzers:
  sideeffects: false

See Also