Expand your Kubernetes knowledge with techniques to make your clusters dynamic and resilient.

DevOps for Developers

The world of DevOps has exploded with the help of technologies like Kubernetes and Docker.
In this course, you will learn about more advanced Kubernetes features such as monitoring, alerting, logging, and scaling - crucial concepts for any DevOps professional. You will learn how to monitor clusters, how to send alerts when potential issues arise, and how to query the whole system’s metrics and logs.
By the end of this course, you will have the required knowledge to make your clusters and applications truly dynamic and resilient, so that they require minimal manual involvement and are self-adaptive.

Kubernetes Monitoring, Logging and Auto-Scaling

So far, the few `HPA` examples used a single custom metric to decide whether to scale the Deployment. You already know from the [Autoscaling Deployments and StatefulSets Based On Resource Usage](https://www.educative.io/pageeditor/10370001/5017680635494400/4994380706349056) chapter that we can combine multiple metrics in an `HPA`. However, all the examples in that chapter used data from the `Metrics Server`. We learned that in many cases memory and CPU metrics from the `Metrics Server` are not enough, so we introduced the `Prometheus Adapter` that feeds custom metrics to the **Metrics Aggregator**. We successfully configured an `HPA` to use those custom metrics. Still, more often than not, we'll need a combination of both types of metrics in our `HPA` definitions. While memory and CPU metrics are not enough by themselves, they are still essential. Can we combine both?

# Combining Metrics Server data with Custom Metrics

Let's take a look at yet another `HPA` definition.

```shell
cat mon/go-demo-5-hpa.yml
```

The **output**, limited to the relevant parts, is as follows.

```yaml
...
  metrics:
  - type: Resource
    resource:
      name: cpu
      targetAverageUtilization: 80
  - type: Resource
    resource:
      name: memory
      targetAverageUtilization: 80
  - type: Object
    object:
      metricName: http_req_per_second_per_replica
      target:
        kind: Service
        name: go-demo-5
      targetValue: 1500m
```

This time, `HPA` has three entries in the `metrics` section. The first two are the "standard" `cpu` and `memory` entries based on the `Resource` type. The last entry is one of the `Object` types we used earlier. With those combined, we're telling `HPA` to scale up if any of the three criteria are met. Similarly, it will scale down as well but for that to happen all three criteria need to be below the targets.



Let's `apply` the definition.

```shell
kubectl -n go-demo-5 \
    apply -f mon/go-demo-5-hpa.yml
```


Next, we'll describe the `HPA`. But, before we do that, we'll have to wait for a bit until the updated `HPA` goes through its next iteration.

```shell
kubectl -n go-demo-5 \
    describe hpa go-demo-5
```

The **output**, limited to the relevant parts, is as follows.

```
...
Metrics:                                                  ( current / target )
  resource memory on pods  (as a percentage of request):  110% (5768533333m) / 80%
  "http_req_per_second_per_replica" on Service/go-demo-5: 825m / 1500m
  resource cpu on pods  (as a percentage of request):     20% (1m) / 80%
...
Deployment pods:                                          5 current / 5 desired
...
Events:
... Message
... -------
... New size: 6; reason: Ingress metric http_req_per_second_per_replica above target
... New size: 9; reason: Ingress metric http_req_per_second_per_replica above target
... New size: 4; reason: Service metric http_req_per_second_per_replica above target
... New size: 3; reason: All metrics below target
... New size: 5; reason: memory resource utilization (percentage of request) above target
```

## `HPA` scaled up the Deployment

We can see that the memory-based metric is above the threshold from the start. In my case, it is `110%`, while the target is `80%`. As a result, `HPA` scaled up the Deployment. In my case, it set the new size to `5` replicas.

There's no need to confirm that the new Pods are running. By now, we should trust `HPA` to do the right thing. 


In this lesson, we will discuss how to combine Metric Server data with Custom Metrics, such that HPA scales up the Deployment.

Combine Metric Server Data with Custom Metrics