prometheus/prometheus

Add proxy_url to targets as meta label

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#17097 opened on Aug 28, 2025

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component/service discoveryhelp wantedkind/enhancementpriority/P3

Description

Problem

I'm working in a network topology of several local private networks which are connected to a global network via a host pc. For service discovery of my targets (the one in the privat networks as well as the host pcs) I use http SD. However, using the PushProx, I have to statically configure the proxy_url per job:

- job_name: "example_job"
    proxy_url: http://host_pc:8080
    http_sd_configs:
      - url: "https://example_SD/local_targets"

This doesnt allow me to dynamically configure the proxies depending on the current state of my network topology.

Proposal

If the proxy url would be (also) passed as a meta label, I could add this url to my http SD and relabel it to cinfigure the proxy, something like this:

- job_name: "example_job"
    http_sd_configs:
      - url: "https://example_SD/local_targets"
      relabel_configs:
        - source_labels: [hostpc]
          target_label: __proxy_url
          replacement: 'http://${1}:8080'

My current approach is to write this dynamic part of the yaml with a script but this is of course a bit unconventional and not ideal.

Contributor guide

Tech stack
go
Domain
backend
Issue type
feature
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
3
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
3-5 days
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
active
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
clear
Prerequisites
Understanding of Prometheus configurationKnowledge of Go programming
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
30
Research direction
Investigate how proxy url is currently implemented in scrape configs. Look at the relabeling code and meta label handling (e.g., address , scheme ). The issue proposes adding proxy url as a meta label. Review the config parsing and scrape target assignment to see how to inject this meta label. Check existing issues or PRs for similar work. Discuss with assignee about implementation approach.