An application where all the essential components are self-contained and deployed within a single process.
If what we ship to our server is a single executable file or script that runs our entire application in one process, we have a monolith on our hands.
If for some reason, our application relies on another service that contains critical features or business logic for our core domain, it's no longer a monolith. It may be a distributed monolith.
When to migrate to microservices
A monolith isn't always a bad thing. In fact, I would advocate for starting out with a monolith on most projects.
Factors that can influence needing to break a monolith into microservices are:
- Growing team size.
- Clear understanding of the subdomains within the code and how they can be assigned to teams.
- Horizonal scaling required for select high-traffic or expensive to operate features in the application.
Difference between a monorepo and a monolith
A monorepo is a code repository that we use to store several related repositories for a project.
A monorepo can become a monolith if when we run an application contained from within a monorepo, it has access to all the components needed in order for it to operate, and all those components are self-contained at runtime.
If we needed to run several processes from within the monorepo in order for the application to work, it's no longer a monolith.
- Ease of local development.
- Ease of deployment.
- Single point of failure.
- Checking in code can turn into a nightmare if the team size is large. Code conflicts might occur more frequently.
- For some applications, it doesn't scale well.