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Service Stats Functionality

This document describes the stats functionality in Zinit, which provides memory and CPU usage information for services and their child processes.

Overview

The stats functionality allows you to monitor the resource usage of services managed by Zinit. It provides information about:

Memory usage (in bytes)
CPU usage (as a percentage)
Child processes and their resource usage

This is particularly useful for monitoring system resources and identifying services that might be consuming excessive resources.

Command Line Usage

To get stats for a service using the command line:

zinit stats <service-name>

Example:

zinit stats nginx

This will output YAML-formatted stats information:

name: nginx
pid: 1234
memory_usage: 10485760  # Memory usage in bytes (10MB)
cpu_usage: 2.5          # CPU usage as percentage
children:               # Stats for child processes
  - pid: 1235
    memory_usage: 5242880
    cpu_usage: 1.2
  - pid: 1236
    memory_usage: 4194304
    cpu_usage: 0.8

JSON-RPC API

The stats functionality is also available through the JSON-RPC API:

Method: `service_stats`

Get memory and CPU usage statistics for a service.

Parameters:

name (string, required): The name of the service to get stats for

Returns:

Object containing stats information:
- name (string): Service name
- pid (integer): Process ID of the service
- memory_usage (integer): Memory usage in bytes
- cpu_usage (number): CPU usage as a percentage (0-100)
- children (array): Stats for child processes
  - Each child has:
    - pid (integer): Process ID of the child process
    - memory_usage (integer): Memory usage in bytes
    - cpu_usage (number): CPU usage as a percentage (0-100)

Example Request:

{
  "jsonrpc": "2.0",
  "id": 1,
  "method": "service_stats",
  "params": {
    "name": "nginx"
  }
}

Example Response:

{
  "jsonrpc": "2.0",
  "id": 1,
  "result": {
    "name": "nginx",
    "pid": 1234,
    "memory_usage": 10485760,
    "cpu_usage": 2.5,
    "children": [
      {
        "pid": 1235,
        "memory_usage": 5242880,
        "cpu_usage": 1.2
      },
      {
        "pid": 1236,
        "memory_usage": 4194304,
        "cpu_usage": 0.8
      }
    ]
  }
}

Possible Errors:

-32000: Service not found
-32003: Service is down

Implementation Details

The stats functionality works by:

Reading process information from /proc/<pid>/ directories on Linux systems
Calculating memory usage from /proc/<pid>/status (VmRSS field)
Calculating CPU usage by sampling /proc/<pid>/stat over a short interval
Identifying child processes by checking the PPid field in /proc/<pid>/status

On non-Linux systems, the functionality provides placeholder values as the /proc filesystem is specific to Linux.

Notes

Memory usage is reported in bytes
CPU usage is reported as a percentage (0-100)
The service must be running to get stats (otherwise an error is returned)
Child processes are identified by their parent PID matching the service's PID

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