==================================
Horizontal Pod Scaler
==================================

Introduction
-------------

If you have read through my blog from the top to the bottom, you will understand the concepts of MicroServices. To annex the learning goal of Scalability I have decided to use a technique called Horizontal Scaling. Before understanding Horizontal Scaling, Vertical Scaling must be first explained as it can paint a clear picture. Vertical Scaling refers to increasing the system resources based on demand. This setup has a few clear disadvantages; no single system can be finitely scaled vertically. Horizontal scaling gets around this problem by introducing multiple pods, meaning the same microservice hosted multiple times. 

Theory
----------

.. image:: https://i.imgur.com/GCzh5cf.png


Execution
----------

I created my first Microservice for the User component. This microservice uses mySQL; for simplicity reasons & the user microservice being a lesser used component in my application. I used my previous Spring Java REST API codebase to quickly set it up. 

Implementation
---------------

Up until this point I implemented the deployment of my Ramses application in my Rancher cluster.

.. image:: https://i.imgur.com/d3JnbTz.png

Rancher is an Kubernetes Management Interface; easily allowing me to deploy my pods in the way I configured them to. One of the services it provides is the implementation of a Loadbalancer; as can be seen here:

.. image:: https://i.imgur.com/6nTPoo6.png

In it is my LoadBalancer configuration. Most of it is auto-generated by Rancher. I've made my own adjustments to the cpu resource, making Rancher scale my pod when the mCPU is met. 

.. code-block:: yaml

    apiVersion: autoscaling/v2
    kind: HorizontalPodAutoscaler
    metadata:
      creationTimestamp: "2022-05-17T11:11:20Z"
      managedFields:
      - apiVersion: autoscaling/v2
        fieldsType: FieldsV1
        fieldsV1:
          f:spec:
            f:maxReplicas: {}
            f:metrics: {}
            f:minReplicas: {}
            f:scaleTargetRef:
              f:apiVersion: {}
              f:kind: {}
              f:name: {}
        manager: rancher
        operation: Update
        time: "2022-05-17T11:11:20Z"
      - apiVersion: autoscaling/v2
        fieldsType: FieldsV1
        fieldsV1:
          f:status:
            f:conditions:
              .: {}
              k:{"type":"AbleToScale"}:
                .: {}
                f:lastTransitionTime: {}
                f:message: {}
                f:reason: {}
                f:status: {}
                f:type: {}
              k:{"type":"ScalingActive"}:
                .: {}
                f:lastTransitionTime: {}
                f:message: {}
                f:reason: {}
                f:status: {}
                f:type: {}
              k:{"type":"ScalingLimited"}:
                .: {}
                f:lastTransitionTime: {}
                f:message: {}
                f:reason: {}
                f:status: {}
                f:type: {}
            f:currentMetrics: {}
            f:currentReplicas: {}
            f:desiredReplicas: {}
            f:lastScaleTime: {}
        manager: k3s
        operation: Update
        subresource: status
        time: "2022-05-17T11:12:35Z"
      name: lb-gameservice
      namespace: ramses
      resourceVersion: "418564"
      uid: a10d1017-32d7-4921-95d5-51fc4ebf228a
    spec:
      maxReplicas: 10
      metrics:
      - resource:
          name: cpu
          target:
            averageValue: 500m
            type: AverageValue
        type: Resource
      minReplicas: 1
      scaleTargetRef:
        apiVersion: apps/v1
        kind: Deployment
        name: gameservice
    status:
      conditions:
      - lastTransitionTime: "2022-05-23T06:17:13Z"
        message: recommended size matches current size
        reason: ReadyForNewScale
        status: "True"
        type: AbleToScale
      - lastTransitionTime: "2022-05-22T17:18:38Z"
        message: the HPA was able to successfully calculate a replica count from cpu resource
        reason: ValidMetricFound
        status: "True"
        type: ScalingActive
      - lastTransitionTime: "2022-05-17T11:12:50Z"
        message: the desired count is within the acceptable range
        reason: DesiredWithinRange
        status: "False"
        type: ScalingLimited
      currentMetrics:
      - resource:
          current:
            averageValue: 1m
          name: cpu
        type: Resource
      currentReplicas: 1
      desiredReplicas: 1
      lastScaleTime: "2022-05-22T14:26:40Z"

Monitoring
-----------

And lastly, I've implemented monitoring metrics to my Rancher, enabling with the help of Grafana to see the metrics granting insight to the pods.

.. image:: https://i.imgur.com/Mjddo3D.png

.. image:: https://i.imgur.com/vkDbaOE.png

.. image:: https://i.imgur.com/b6GaFsn.png