Host (shell) application
The host, or shell, is the application the browser loads first in a micro-frontend architecture; it provides layout, navigation and session, and loads the remotes.
The host owns the things that must exist only once in a micro-frontend product: the top-level layout, the main navigation, the top-level routes, the session and the configuration of shared libraries. It contains little or no business functionality. That lives in the remotes it loads at runtime.
A good host is small and changes rarely. Every remote depends on it, so every change to the host is a change to the whole product.
Example
A back-office product has a shell with a sidebar and a header. Its route table maps URL prefixes to remotes:
/customersloads the customers remote./invoicesloads the invoices remote./settingsloads the settings remote.
The shell reads a manifest at startup to find where each remote is deployed. It loads each remote only when the user navigates to its route. If a remote fails to load, the shell shows an error panel for that area and the rest of the product keeps working.
Common misunderstanding
Teams often let the host grow into a second monolith. Shared services, business rules and utility code pile up there because it is the one place everyone can reach. After a while, no remote can be released without a host release, and the independence is gone.
Keep shared code in versioned libraries. Limit the host to layout, routing, authentication and error handling, and give it a clear owner. In a migration, the host can also be the place where the legacy application is mounted as one more remote while new ones replace it. The micro-frontends page describes this split.
Why it matters. The host defines the contract that every remote must follow, so its design decides how independent teams really are. In a migration it is the frame in which old and new applications coexist.
Related terms
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