CAReplicatorLayer

class RepeatingCircle: UIView {

    let replicatorLayer = CAReplicatorLayer()
    let circle = CALayer()

    let duration: TimeInterval = 1.0
    let circleSize: CGFloat = 15
    let instanceCount = 20

    override func draw(_ rect: CGRect) {

        replicatorLayer.frame = rect
        replicatorLayer.instanceCount = instanceCount
        replicatorLayer.instanceDelay = duration / CFTimeInterval(instanceCount)

        let angle = -CGFloat.pi * 2 / CGFloat(instanceCount)
        replicatorLayer.instanceTransform = CATransform3DMakeRotation(angle, 0, 0, 1)

        circle.frame = CGRect(origin: CGPoint.zero,
                              size: CGSize(width: circleSize, height: circleSize))
        circle.backgroundColor = UIColor.blue.cgColor
        circle.cornerRadius = circleSize / 2
        replicatorLayer.addSublayer(circle)

        circle.add(animation: "transform.scale", fromValue: 1, toValue: 0.2, duration: duration)
        circle.add(animation: "opacity", fromValue: 1, toValue: 0, duration: duration)

        self.layer.addSublayer(replicatorLayer)
    }

}

extension CALayer {

    func add(animation: String, fromValue: Double, toValue: Double, duration: Double) {
        let animation = CABasicAnimation(keyPath: animation)
        animation.fromValue = fromValue
        animation.toValue = toValue
        animation.duration = duration
        animation.repeatCount = Float.greatestFiniteMagnitude
        self.add(animation, forKey: nil)
    }
}