prometheus/prometheus

__meta_kubernetes_service_loadbalancer_ip not working as expected

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#14,398 opened on Jul 3, 2024

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component/service discoverycomponent/service discovery/kubernetesgood first issuehelp wanted

Description

What did you do?

used following config snippet to set LB service external IP as param_target for DNS probes

....
      relabel_configs:
      - action: keep
        regex: powerdns-external;pdns-udp
        source_labels:
        - __meta_kubernetes_service_name
        - __meta_kubernetes_service_port_name
      - source_labels:
        - __meta_kubernetes_service_loadbalancer_ip
        target_label: __param_target
...

now with following config __param_target not set, it is empty. If I check powerdns-external service I see that it has loadBalancer IP only under status.loadBalancer.ingress so no .spec.loadBalancerIP defined automatically, looks like after 1.24 Kubernetes dropped this .spec.loadBalancerIP setting.

apiVersion: v1
kind: Service
metadata:
  name: powerdns-external
.....
status:
  loadBalancer:
    ingress:
      - ip: 192.168.1.15
spec:
  ports:
    - name: pdns-udp
      protocol: UDP
      port: 53
      targetPort: 53
      nodePort: 30937
  selector:
    application: powerdns
  clusterIP: 10.96.26.217
  clusterIPs:
    - 10.96.26.217
  type: LoadBalancer
  sessionAffinity: None
  externalTrafficPolicy: Cluster
  ipFamilies:
    - IPv4
  ipFamilyPolicy: SingleStack
  allocateLoadBalancerNodePorts: true
  internalTrafficPolicy: Cluster

Main point if I set .spec.loadBalancerIP manually from service then scrape job starts to work and thus __meta_kubernetes_service_loadbalancer_ip returns loadBalancerIP value. So could it be that __meta_kubernetes_service_loadbalancer_ip relies on .spec.loadBalancerIP and not compatible with latest Kubernetes?

What did you expect to see?

No response

What did you see instead? Under which circumstances?

__meta_kubernetes_service_loadbalancer_ip returned no value

System information

No response

Prometheus version

No response

Prometheus configuration file

No response

Alertmanager version

No response

Alertmanager configuration file

No response

Logs

No response

Contributor guide

Tech stack
go
Domain
backenddevops
Issue type
bug
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
4
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
1-2 days
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
blocked
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
mostly clear
Prerequisites
GoKubernetes service discovery
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
20
Research direction
The issue is that meta kubernetes service loadbalancer ip is populated from spec.loadBalancerIP but in Kubernetes 1.24+, the load balancer IP is stored in status.loadBalancer.ingress. The fix would involve modifying the Kubernetes service discovery code in Prometheus (likely in discover/kubernetes/) to also check status.loadBalancer.ingress[].ip when spec.loadBalancerIP is empty. Review the relevant Go source files and ensure backward compatibility. The issue has an assignee, so coordinate with them if necessary.
__meta_kubernetes_service_loadbalancer_ip not working as expected · prometheus/prometheus#14398 | Good First Issue