# README

PSConfig

PSConfig is a utility library, built to load values from AWS SSM Param Store into a custom configuration struct for your application. It is partially inspired by ianlopshire/go-ssm-config, but allows for nested configuration elements. In our projects we will typically have a config defined like this:

type HTTPConfig struct {
	Port          int           `hcl:"port"`
	ReadTimeout   time.Duration `hcl:"read_timeout"`
	WriteTimeout  time.Duration `hcl:"write_timeout"`
}

type DbConfig struct {
	Host        string `hcl:"host"`
	Username    string `hcl:"username"`
	Password    string `hcl:"password"`
	Name        string `hcl:"name"`
	Application string `hcl:"application"`
}

type ApplicationConfig struct {
	HTTP HTTPConfig `hcl:"http"`
	DB   DBConfig   `hcl:"db"`
}

This would typically be in an HCL file like:

http {
  port           = 8080
  read_timeout   = "${duration("5s")}"
  write_timeout  = "${duration("2m")}"
}

db {
  host                  = "database-server:5432"
  username              = "username"
  password              = "passw0rd!"
  application           = "fancy-application-name"
  name                  = "database_name"
}

Since we have relatively complicated configuration needs, grouping by the types of configuration made our lives easier.

Motivation

We wanted to move our configuration from templated HCL files, into the param store, to make it easier to manage configuration in general. Because of our current config structs, we needed to have something that minimized the amount of application changes we had to make, so we developed this library to allow us to load arbitrarily nested param store items into an equally arbitrarily nested config struct.

Usage

Assume you have already set some parameters in AWS SSM Param Store:

Name	Value	Type
/env/application/http/port	8080	String
/env/application/http/read_timeout	5s	String
/env/application/http/write_timeout	8080	String
/env/application/db/host	database-server:5432	String
/env/application/db/username	username	String
/env/application/db/password	passw0rd	SecureString
/env/application/db/application	fancy-application-name	String
/env/application/db/name	database_name	String

You can then write code like the following:

package main

import (
	"encoding/json"
	"fmt"
	"log"
	"time"

	psconfig "github.com/seniorlink-vela/go-param-store-config"
)

type HTTPConfig struct {
	Port         int           `ps:"port"`
	ReadTimeout  time.Duration `ps:"read_timeout"`
	WriteTimeout time.Duration `ps:"write_timeout"`
}

type DbConfig struct {
	Host        string `ps:"host"`
	Username    string `ps:"username"`
	Password    string `ps:"password"`
	Name        string `ps:"name"`
	Application string `ps:"application"`
}

type ApplicationConfig struct {
	HTTP HTTPConfig `ps:"http"`
	DB   DbConfig   `ps:"db"`
}

func main() {
	c := &ApplicationConfig{}
	err := psconfig.Load("us-east-1", "/env/application/", c)
	if err != nil {
		log.Fatal(err.Error())
	}
	j, err := json.MarshalIndent(c, "", "  ")
	if err != nil {
		log.Fatal(err.Error())
	}
	fmt.Printf("%s\n", j)
}

The output of this is:

{
  "HTTP": {
    "Port": 8085,
    "ReadTimeout": 5000000000,
    "WriteTimeout": 120000000000
  },
  "DB": {
    "Host": "database-server:5432",
    "Username": "username",
    "Password": "passw0rd",
    "Name": "database_name",
    "Application": "fancy-application-name"
  }
}