Crystal Language Web App

Crystal combines Ruby-like syntax with compiled language performance, producing statically-typed, memory-safe binaries that rival C in speed. The Kemal framework brings Sinatra-style simplicity to Crystal. This guide covers building and deploying Crystal web applications on a VPS.

Installing Crystal

# Ubuntu/Debian
curl -fsSL https://crystal-lang.org/install.sh | sudo bash

# Or manual installation
sudo apt install crystal

# Verify
crystal --version

Project Setup

# Create project
crystal init app myapp
cd myapp

# shard.yml (Crystal package manager)
dependencies:
  kemal:
    github: kemalcr/kemal
  pg:
    github: will/crystal-pg
  db:
    github: crystal-lang/crystal-db
  json:
    github: crystal-lang/json

# Install dependencies
shards install

Application Code

# src/myapp.cr
require "kemal"
require "json"
require "db"
require "pg"

# Database connection
DB_URL = ENV.fetch("DATABASE_URL", "postgres://localhost/myapp_dev")
DATABASE = DB.open(DB_URL)

# Models
class User
  include JSON::Serializable
  property id : Int32
  property name : String
  property email : String

  def initialize(@id, @name, @email); end
end

# Routes
get "/health" do |env|
  env.response.content_type = "application/json"
  {status: "healthy"}.to_json
end

get "/api/users" do |env|
  env.response.content_type = "application/json"
  users = [] of User
  DATABASE.query("SELECT id, name, email FROM users") do |rs|
    rs.each do
      users