prom-mock-rs

A mock Prometheus HTTP API server for integration testing, available both as a library and CLI application.

Overview

This project provides a lightweight mock implementation of the Prometheus HTTP API, designed for testing applications that integrate with Prometheus. It supports configurable response fixtures, artificial latency, error injection, and in-memory metrics storage.

Features

Remote Write API: Compatible with Prometheus remote write protocol
Query API: Basic query endpoint support for stored metrics
Fixture System: YAML-based predefined responses
Mock Behavior: Configurable latency and error rates
In-Memory Storage: Temporary metrics storage for testing scenarios
Library API: Use as a Rust library in your tests
CLI Application: Standalone server for integration testing

Installation

Prerequisites

This library requires Rust 1.76.0 or later.

As a CLI tool

cargo install prom-mock-rs

As a library dependency

[dependencies]
prom-mock-rs = "0.1.0"

Usage

CLI Application

Basic Usage

prom-mock --listen 127.0.0.1:9090

With Fixtures

prom-mock --fixtures fixtures.yaml --listen 127.0.0.1:9090

Configuration Options

--listen: Address to listen on (default: 127.0.0.1:19090)
--fixtures: Path to YAML fixture file
--latency: Artificial response delay (e.g., 100ms, 1s)
--error-rate: Probability of 503 errors (0.0-1.0)
--fixed-now: Fixed "now" time for testing (ISO-8601 format)

Library Usage

use std::sync::Arc;
use prom_mock_rs::{MemoryStorage, http::build_router};

#[tokio::main]
async fn main() -> std::io::Result<()> {
    // Create storage and app state
    let storage = Arc::new(MemoryStorage::new());
    let state = prom_mock_rs::http::AppState::builder()
        .with_storage(storage)
        .build()?;
    
    // Build the router
    let app = build_router(state);
    
    // Serve with axum
    let listener = tokio::net::TcpListener::bind("127.0.0.1:19090").await?;
    axum::serve(listener, app).await
}

API Endpoints

POST /api/v1/write - Remote write endpoint
GET /api/v1/query - Query endpoint
GET /health - Health check

Fixture Format

version: 1
defaults:
  status: 200
  latency: "100ms"
routes:
  - path: "/api/v1/query"
    method: "GET"
    response:
      status: 200
      body: |
        {"status":"success","data":{"resultType":"vector","result":[]}}

Development

# Run tests
cargo test

# Run the CLI with development settings
cargo run --bin prom-mock -- --listen 127.0.0.1:9090 --fixtures tests/fixtures.yaml

# Build the library
cargo build

# Check library documentation
cargo doc --open

Library API

The library exposes several key components:

Storage Traits: Storage and MetadataStorage for implementing custom backends
Memory Storage: MemoryStorage - ready-to-use in-memory implementation
Query Engine: SimpleQueryEngine for parsing and executing basic PromQL queries
Label Matchers: Extensible label filtering (EqualMatcher, RegexMatcher, etc.)
HTTP Layer: build_router() and AppState for creating HTTP servers
Fixtures: FixtureBook for loading predefined responses

License

MIT

prom-mock-rs 0.2.0