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Host composition ​

VerifiedInferred

This page explains how a vertical application composes the reusable platform. It is the practical companion to the host composition execution map.

Verified anchors ​

text
NGB.PropertyManagement.Api/Program.cs
NGB.PropertyManagement.BackgroundJobs/Program.cs
NGB.PropertyManagement.Watchdog/Program.cs
NGB.PropertyManagement.Migrator/Program.cs
NGB.Migrator.Core/PlatformMigratorCli.cs

What host composition means in NGB ​

NGB keeps the reusable platform in library projects and lets each vertical host compose those projects explicitly.

That gives you three important properties:

  • the platform core stays reusable;
  • each vertical decides which modules it brings in;
  • operational hosts such as API, migrator, background jobs, and watchdog stay small and focused.

The API host pattern ​

The verified NGB.PropertyManagement.Api/Program.cs file shows the canonical pattern:

  1. build a standard ASP.NET Core host;
  2. add observability and health checks;
  3. validate the application connection string;
  4. register AddNgbRuntime();
  5. register AddNgbPostgres(connectionString);
  6. register vertical modules and runtime/postgres extensions;
  7. add controllers, auth, error handling, and app-specific services;
  8. build the app and map controllers.

That is the most important composition rule in the platform: hosts compose, libraries execute.

The background jobs host pattern ​

NGB.PropertyManagement.BackgroundJobs/Program.cs shows a second canonical host shape.

It uses the platform background-jobs bootstrap first, ensures infrastructure, then composes the same runtime and PostgreSQL modules as the API host plus a background-jobs module for the vertical.

That means background processing is not a special side system. It runs on the same platform execution core.

The watchdog host pattern ​

NGB.PropertyManagement.Watchdog/Program.cs shows the health/operability host.

It is intentionally thin:

  • add NGB watchdog hosting;
  • build the app;
  • use watchdog middleware;
  • map watchdog endpoints.

This keeps health UI and service status concerns separate from the main business API.

The migrator host pattern ​

NGB.PropertyManagement.Migrator/Program.cs shows the migrator host pattern:

  • force-load vertical PostgreSQL assembly for deterministic migration-pack discovery;
  • branch into seed-defaults or seed-demo commands if requested;
  • otherwise delegate to PlatformMigratorCli.

That makes the migrator a proper application host, not just a shell script.

Why this pattern matters ​

Host composition is one of the strongest NGB architectural choices.

It lets the platform stay modular without turning everything into distributed services. The result is a modular monolith with distinct operational entry points.

Released under the Apache License 2.0.

Copyright © NGB Platform