# ngcc parallel build support ## background Running multiple instances of ngcc at the same time is not supported, since it can cause difficult to debug corrupt builds. To help developers who fall foul of this scenario, we implemented a lockfile approach, where ngcc will fail if there is already another process running from the same `@angular/compiler-cli` package. The Angular CLI has an integration with ngcc where it triggers ngcc for every external import path that is found during TS compil