Independent Deployment

Independent Deployment sits at the heart of deployment in single-spa. This guide walks through the concept step by step, with examples, a cheatsheet, and common mistakes to avoid.

Independent Deployment Overview

Independent Deployment is a building block you will reach for often in single-spa. It keeps related logic together and makes your intent obvious to reviewers and future maintainers.

When you learn independent deployment properly, you avoid the guesswork that leads to bugs and rework. The example below shows the shape you will use in most real single-spa projects.

# each micro frontend publishes its own bundle + import-map entry
@org/checkout -> https://cdn.example.com/checkout/v3/checkout.js

# update only this app's import-map entry to release it
{ "@org/checkout": "https://cdn.example.com/checkout/v3/checkout.js" }

Deploying a micro frontend is often just updating its import-map URL.

Independent Deployment Example

registerApplication({
  name: '@org/app',
  app: () => System.import('@org/app'),
  activeWhen: ['/app'],
});
start();

Start from a minimal Independent Deployment example and grow it only as needed.
Keep configuration explicit so Independent Deployment behaves the same in every environment.
Name things clearly so teammates understand your Independent Deployment at a glance.
Add tests around Independent Deployment early to lock in expected behaviour.

Single-SPA Cheatsheet

Core single-spa APIs related to independent deployment.

API	Example	Purpose
registerApplication	`registerApplication({ name, app, activeWhen })`	Register a micro frontend
activeWhen	`activeWhen: ['/checkout']`	Route ownership
start	`start()`	Begin routing
bootstrap	`export async function bootstrap()`	One-time setup
mount	`export async function mount(props)`	Render the app
unmount	`export async function unmount(props)`	Clean up the app
import map	`systemjs-importmap`	Locate app bundles

How Independent Deployment Works in Single-SPA

Independent Deployment is part of how single-spa lets multiple applications — even in different frameworks — coexist on one page. A root config registers each app and controls when it is active.

Deploying a micro frontend is often just updating its import-map URL.

A root config registers apps and calls start().
Each app exports bootstrap, mount, and unmount lifecycles.
activeWhen decides which routes each app owns.
Import maps resolve each app's bundle at runtime.

Practical Guidance for Independent Deployment

For reliable micro frontends, independent deployment should isolate failures and keep shared state minimal. Let each team own its app end to end while agreeing on a few shared contracts.

Concern	Recommendation
Isolation	One app's crash should not break others
Shared state	Prefer shared utility modules over globals
Routing	Keep activeWhen rules explicit and non-overlapping
Deployment	Release via import-map updates per app

Common Mistakes

Skipping error handling and edge cases when wiring up independent deployment.
Leaving independent deployment untested, so regressions slip into production.
Over-engineering independent deployment before you actually need the extra flexibility.
Ignoring documentation, which makes independent deployment hard for the next developer to change.

Key Takeaways

Independent Deployment is a core part of working effectively with single-spa.
Start small and keep independent deployment focused on a single responsibility.
Apply consistent patterns so independent deployment scales across your project.
Test and document independent deployment to keep it maintainable over time.

Pro Tip

Pair independent deployment with automated tests from day one. It is far cheaper to catch single-spa regressions in CI than in production.