A service for handling user inquiries A user can send a report Admins can process reports An admin can give feedback to the user DAU = 100 Availability = 99.95% RPS = 100

For a user request processing service with such requirements (DAU=100, Availability=99.95%, RPS=100), the following architecture and approaches in Go can be proposed:

1. API for users:

• Endpoint for creating reports (POST /reports).
• Validation and saving of reports to the database.

2. API for admins:

• Retrieving a list of reports with filters and pagination.
• Processing reports (changing status, adding comments).
• Sending feedback to users (e.g., via email or push notifications).

3. Technologies:

• Go for backend using frameworks like Gin or Echo.
• Database: PostgreSQL or MongoDB for storing reports.
• Caching (Redis) to speed up reading frequently requested data.

4. Ensuring availability (99.95%):

• Horizontal scaling of the service.
• Using health checks and automatic restart.
• Database replication.

5. Handling load (RPS=100):

• Go handles high load well thanks to goroutines.
• Use a connection pool to the database.

Example of a simple report creation handler in Go with Gin:

package main

import (
    "net/http"
    "github.com/gin-gonic/gin"
)

type Report struct {
    UserID  string `json:"user_id" binding:"required"`
    Message string `json:"message" binding:"required"`
}

func createReport(c *gin.Context) {
    var report Report
    if err := c.ShouldBindJSON(&report); err != nil {
        c.JSON(http.StatusBadRequest, gin.H{"error": err.Error()})
        return
    }
    // TODO: save report to DB
    c.JSON(http.StatusCreated, gin.H{"status": "report created"})
}

func main() {
    r := gin.Default()
    r.POST("/reports", createReport)
    r.Run(":8080")
}

This service can be extended by adding authentication, authorization, notifications, and analytics.