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docs: example for the usage of Analyses (#2168)
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Signed-off-by: Florian Bacher <florian.bacher@dynatrace.com>
Co-authored-by: RealAnna <89971034+RealAnna@users.noreply.github.com>
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# Metric Analysis

This example shows how the `Analysis` feature of the `metrics-operator` can be used to
define goals for metric values and evaluate them.

## Difference between `Analysis` and `Evaluations`

`Evaluations` provide an easy way of checking whether the current value of a `KeptnMetric` fulfills
a requirement, i.e. is below or above a certain threshold.
This is ideal for doing simple checks, such as validating that a cluster currently has
enough resources for the pod of a deployment to be scaled up.
In other cases however, it may not be enough to just check the current value of a metric (e.g. the number of
available resources), but one may want to evaluate the value of a metric for a specific timeframe.
For example, one may execute load tests for a service after it has been deployed, and then verify
if performance-related metrics, such as response time or error rate during the time
when the tests have been executed, meet certain criteria.
That is where the `Analysis` capabilities of the `metrics-operator` come in.

## Defining Metrics

The first step using this feature is to figure out what it is we want to analyze.
In our example, we would like to analyze the response time and the error rate for a service.
Let's assume those metrics are retrieved from Prometheus, so first we're going to create a `KeptnMetricsProvider`.
Just like when using `KeptnMetrics`, the provider will tell Keptn where to retrieve the values we are interested in.

To create the provider, execute the following commands from this directory:

```shell
kubectl create namespace analysis-demo
```

```shell
cat <<EOF | kubectl apply -f -
apiVersion: metrics.keptn.sh/v1alpha3
kind: KeptnMetricsProvider
metadata:
name: my-provider
namespace: analysis-demo
spec:
type: prometheus
targetServer: "http://prometheus-k8s.monitoring.svc.cluster.local:9090"
EOF
```

Next, we will define the queries for the metrics we are interested in.
This is done by creating an `AnalysisValueTemplate` for each of the metrics.
Both of these `AnalysisValueTemplates` will refer to the provider we just created and therefore
retrieve the values from the Prometheus server the provider is pointing to.
As the name `AnalysisValueTemplate` suggests, this resource benefits from the support of the
go templating syntax, with which we can include placeholders, e.g. for the name of the workload, in the query.
This way, the same `AnalysisValueTemplate` can be reused for different workloads, if the query
for retrieving the value relevant for them only differs in e.g. their label selectors.
With that being said, let's apply the `AnalysisValueTemplates` to our cluster.
First, we are going to create the template for the response time:

```shell
cat <<EOF | kubectl apply -f -
apiVersion: metrics.keptn.sh/v1alpha3
kind: AnalysisValueTemplate
metadata:
name: response-time-p95
namespace: analysis-demo
spec:
provider:
name: my-provider
query: 'histogram_quantile(0.95, sum by(le) (rate(http_server_request_latency_seconds_bucket{job="{{.workload}}"}[1m])))'
EOF
```

Our second metric will be the error rate, which we will retrieve with the following template:

```shell
cat <<EOF | kubectl apply -f -
apiVersion: metrics.keptn.sh/v1alpha3
kind: AnalysisValueTemplate
metadata:
name: error-rate
namespace: analysis-demo
spec:
provider:
name: my-provider
query: 'rate(http_requests_total{status_code="500", job="{{.workload}}"}[1m]) or on() vector(0)'
EOF
```

### Setting up Prometheus

#### Option 1: Using real data from podtato-head

The queries provided to these `AnalysisValueTemplates` rely on actual data coming from Prometheus, particularly
the data for the **podtato-head** application that has been deployed in the [sample-app example](../../sample-app/README.md).
Also, this example assumes you have prometheus installed in your cluster, which can be done
by following the instructions in the [observability-example](../observability/README.md).

When you have done so, you also need to make sure that the podtato-head application is monitored by Prometheus by
creating a Prometheus `ServiceMonitor`.
Ths can be done by applying the manifest in `./config/service-monitor.yaml`:

```shell
kubectl apply -f ./config/service-monitor.yaml
```

#### Option 2: Using Mockserver

If you do not want to go through the process of deploying an actual application and setting up Prometheus, you can also use
[MockServer](https://www.mock-server.com) to fake the monitoring data.
To deploy the mock server, use the following command:

```shell
kubectl apply -f ./config/mock-server.yaml
```

Once the MockServer is up and running, we will adjust the `KeptnMetricsProvider` to retrieve data from there,
rather than from a real Prometheus instance:

```shell
cat <<EOF | kubectl apply -f -
apiVersion: metrics.keptn.sh/v1alpha3
kind: KeptnMetricsProvider
metadata:
name: my-provider
namespace: analysis-demo
spec:
type: prometheus
targetServer: "http://mockserver.analysis-demo.svc.cluster.local:1080"
EOF
```

## Defining goals for the metrics

Now that we have defined our metrics, it is time to describe what we expect from these values.
This is done in an `AnalysisDefinition`, which can be applied using the following command:

```shell
cat <<EOF | kubectl apply -f -
apiVersion: metrics.keptn.sh/v1alpha3
kind: AnalysisDefinition
metadata:
name: my-analysis-definition
namespace: analysis-demo
spec:
objectives:
- analysisValueTemplateRef:
name: response-time-p95
target:
failure:
greaterThan:
fixedValue: 500m
warning:
greaterThan:
fixedValue: 300m
weight: 1
keyObjective: false
- analysisValueTemplateRef:
name: error-rate
target:
failure:
greaterThan:
fixedValue: 0
weight: 1
keyObjective: true
totalScore:
passPercentage: 60
warningPercentage: 50
EOF
```

## Executing an Analysis

Finally, now that we have all of our metrics and our goals defined, we can apply an instance of the `Analysis` CRD
to perform an analysis for a specific timeframe:

```shell
cat <<EOF | kubectl apply -f -
apiVersion: metrics.keptn.sh/v1alpha3
kind: Analysis
metadata:
name: analysis-sample
namespace: analysis-demo
spec:
timeframe:
from: 2023-09-25T13:10:00Z
to: 2023-09-25T13:15:00Z
args:
"workload": "podtato-head-frontend"
analysisDefinition:
name: my-analysis-definition
EOF
```

Once applied, the status of the analysis can be checked with:

```shell
kubectl get analyses -n analysis-demo
```

This command should yield a list of all analyses within our `analysis-demo` namespace,
together with the current status of the analysis.
In our case, we will receive one analysis which has already completed and has passed:

```shell
NAME ANALYSISDEFINITION STATE WARNING PASS
analysis-sample my-analysis-definition Completed true
```

Please note that this example uses real data from an actual service monitored by Prometheus,
so it could very well be that the result of your analysis might be a different one,
as those values heavily depend on the environment this example is executed in.

To get further details on the analysis, we can also retrieve the complete yaml representation:

```shell
kubectl get analyses -n analysis-demo analysis-sample -oyaml
```

This will return something like the following, and includes the `status.raw` field, which contains a detailed
breakdown on the result of each objective evaluation.

```yaml
apiVersion: metrics.keptn.sh/v1alpha3
kind: Analysis
metadata:
name: analysis-sample
namespace: analysis-demo
spec:
analysisDefinition:
name: my-analysis-definition
args:
workload: podtato-head-frontend
timeframe:
from: "2023-09-25T13:10:00Z"
to: "2023-09-25T13:15:00Z"
status:
pass: true
raw: '{"objectiveResults":[{"result":{"failResult":{"operator":{"greaterThan":{"fixedValue":"500m"}},"fulfilled":false},"warnResult":{"operator":{"greaterThan":{"fixedValue":"300m"}},"fulfilled":false},"warning":false,"pass":true},"objective":{"analysisValueTemplateRef":{"name":"response-time-p95"},"target":{"failure":{"greaterThan":{"fixedValue":"500m"}},"warning":{"greaterThan":{"fixedValue":"300m"}}},"weight":1},"value":0.00475,"score":1},{"result":{"failResult":{"operator":{"greaterThan":{"fixedValue":"0"}},"fulfilled":false},"warnResult":{"operator":{},"fulfilled":false},"warning":false,"pass":true},"objective":{"analysisValueTemplateRef":{"name":"error-rate"},"target":{"failure":{"greaterThan":{"fixedValue":"0"}}},"weight":1,"keyObjective":true},"value":0,"score":1}],"totalScore":2,"maximumScore":2,"pass":true,"warning":false}'
state: Completed
```
## Interpreting the Analysis result breakdown
The `status.raw` field is a string encoded JSON object object that represents the
results of evaluating one or more performance objectives or metrics.
It shows whether these objectives have passed or failed, their actual values, and the associated scores.
In this example, the objectives include response time and error rate analysis,
each with its own criteria for passing or failing.
The overall evaluation has passed, and no warnings have been issued.

```json
{
"objectiveResults": [
{
"result": {
"failResult": {
"operator": {
"greaterThan": {
"fixedValue": "500m"
}
},
"fulfilled": false
},
"warnResult": {
"operator": {
"greaterThan": {
"fixedValue": "300m"
}
},
"fulfilled": false
},
"warning": false,
"pass": true
},
"objective": {
"analysisValueTemplateRef": {
"name": "response-time-p95"
},
"target": {
"failure": {
"greaterThan": {
"fixedValue": "500m"
}
},
"warning": {
"greaterThan": {
"fixedValue": "300m"
}
}
},
"weight": 1
},
"value": 0.00475,
"score": 1
},
{
"result": {
"failResult": {
"operator": {
"greaterThan": {
"fixedValue": "0"
}
},
"fulfilled": false
},
"warnResult": {
"operator": {
},
"fulfilled": false
},
"warning": false,
"pass": true
},
"objective": {
"analysisValueTemplateRef": {
"name": "error-rate"
},
"target": {
"failure": {
"greaterThan": {
"fixedValue": "0"
}
}
},
"weight": 1,
"keyObjective": true
},
"value": 0,
"score": 1
}
],
"totalScore": 2,
"maximumScore": 2,
"pass": true,
"warning": false
}
```

The meaning of each of these properties is as follows:

**`objectiveResults`**: This is an array containing one or more objects,
each representing the results of a specific objective or performance metric.

- The first item in the array:
- **`result`**: This object contains information about whether the objective has passed or failed.
It has two sub-objects:
- **`failResult`**: Indicates whether the objective has failed.
In this case, it checks if a value is greater than 500 milliseconds, and it hasn't been fulfilled (`fulfilled: false`).
- **`warnResult`**: Indicates whether the objective has issued a warning.
It checks if a value is greater than 300 milliseconds, and it hasn't been fulfilled (`fulfilled: false`).
<!-- markdownlint-disable-next-line -->
- **`warning`**: Indicates whether a warning has been issued (false in this case).
- **`pass`**: Indicates whether the objective has passed (true in this case).
- **`objective`**: Describes the objective being evaluated.
It includes:
- **`analysisValueTemplateRef`**: Refers to the template used for analysis (`response-time-p95`).
- **`target`**: Sets the target values for failure and warning conditions.
In this case, failure occurs if the value is greater than 500 milliseconds,
and warning occurs if it's greater than 300 milliseconds.
- **`weight`**: Specifies the weight assigned to this objective (weight: 1).
- **`value`**: Indicates the actual value measured for this objective (value: 0.00475).
- **`score`**: Indicates the score assigned to this objective (score: 1).

- The second item in the array:
- **`result`**: Similar to the first objective, it checks whether a value is
greater than 0 and has not been fulfilled (`fulfilled: false`).
There are no warning conditions in this case.
- **`objective`**: Describes the objective related to error rate analysis.
- **`analysisValueTemplateRef`**: Refers to the template used for analysis (`error-rate`).
- **`target`**: Sets the target value for failure (failure occurs if the value is greater than 0).
- **`weight`**: Specifies the weight assigned to this objective (weight: 1).
- **`keyObjective`**: Indicates that this is a key objective (true).

- **`value`**: Indicates the actual value measured for this objective (value: 0).
- **`score`**: Indicates the score assigned to this objective (score: 1).

**`totalScore`**: Represents the total score achieved based on the objectives evaluated (totalScore: 2).

**`maximumScore`**: Indicates the maximum possible score (maximumScore: 2).

**`pass`**: Indicates whether the overall evaluation has passed (true in this case).
<!-- markdownlint-disable-next-line -->
**`warning`**: Indicates whether any warnings have been issued during the evaluation (false in this case).
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