How to add additional scrape config to Prometheus - kubernetes

Question

I want to add an additional scrape config into Prometheus. I have followed the below method.
https://github.com/prometheus-operator/prometheus-operator/blob/main/Documentation/additional-scrape-config.md
First, created a file prometheus-additional.yaml and added the new config
- job_name: "prometheus"
static_configs:
- targets: ["localhost:9090"]
Secondly, created a secret out of it.
kubectl create secret generic additional-scrape-configs --from-file=prometheus-additional.yaml --dry-run -oyaml > additional-scrape-configs.yaml
Then created the secret using the below command
kubectl apply -f additional-scrape-configs.yaml -n monitoring
Then in the above link it says
"Finally, reference this additional configuration in your prometheus.yaml CRD."
apiVersion: monitoring.coreos.com/v1
kind: Prometheus
metadata:
name: prometheus
labels:
prometheus: prometheus
spec:
replicas: 2
serviceAccountName: prometheus
serviceMonitorSelector:
matchLabels:
team: frontend
additionalScrapeConfigs:
name: additional-scrape-configs
key: prometheus-additional.yaml
Where I can find the above? Do I need to create a new CRD? Can't I update the existing running deployment?

Answer 1

This is somehow wrong in the Documentation, you have to use additionalScrapeConfigsSecret:
additionalScrapeConfigsSecret:
enabled: true
name: additional-scrape-configs
key: prometheus-additional.yaml
Else you get the error cannot unmarshal !!map into []yaml.MapSlice
Here is a better documentation:
https://github.com/prometheus-community/helm-charts/blob/8b45bdbdabd9b54766c4beb3c562b766b268a034/charts/kube-prometheus-stack/values.yaml#L2691
According to this, you could add scrape configs without packaging into a secret like this:
additionalScrapeConfigs: |
- job_name: "prometheus"
static_configs:
- targets: ["localhost:9090"]

Answer 2

That document applies to prometheus-operator. If you have deployed it, you should have your Prometheus CRD:
kubectl get prometheus -n monitoring
Then you can edit the Prometheus exactly as stated in above: adding additionalScrapeConfigs key in the spec. (after adding a secret)
After editing, new scrape configs will be reloaded and applied automatically (conf-reloaders).