Limit the cardinality of request metrics

Description

Contributor guide

Tech stack

java

Domain

backendperformanceobservability

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.

stale

ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.

mostly clear

Prerequisites

JavaMicrometer metricsarmeria metrics system

Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.

40

Research direction

First, study how armeria currently collects request metrics and identifies the number of unique tag combinations. Then, look at RestTemplate's implementation for logging warnings and refusing high cardinality metrics. Finally, implement a similar guardrail in armeria's metric collection, possibly adding configuration options for maximum cardinality.