vapor-docs/3.0/docs/getting-started/application.md

Application

Every Vapor project has an Application. You use the application to create any services you might need while developing.

The best place to access the application is in your project's boot.swift file.

import Vapor

public func boot(_ app: Application) throws {
    // your code here
}

You can also access the application from your routes.swift file. It's stored as a property there.

import Vapor

final class Routes: RouteCollection {
    ...
}

Unlike some other web frameworks, Vapor doesn't support statically accessing the application. If you need to access it from another class or struct, you should pass through a method or initializer.

!!! info Avoiding static access to variables helps make Vapor performant by preventing the need for thread-safe locks or semaphores.

Services

The application's main function is to make services. For example, you might need a BCryptHasher to hash some passwords before storing them in a database. You can use the application to create one.

import BCrypt

let bcryptHasher = try app.make(BCryptHasher.self)

Or you might use the application to create an HTTP client.

let client = try app.make(Client.self)
let res = client.get("http://vapor.codes")

Learn more about services in Getting Started → Services.