Intro

Krabs is an Express.js middleware that allows you to serve hundreds of different websites using only one Express.js and Next.js instance.

Multitenancy is a reference to the mode of operation of software where multiple independent instances of one or multiple applications operate in a shared environment. The instances (tenants) are logically isolated, but physically integrated. (source)

Thanks to Krabs, we can host multiple websites inside of our Next.js instance and serve them separately depending on the domain that the user is browsing:

Use Cases

There are different reasons why you may want to achieve multi-tenancy with Next.js. First of all, it's probably the best React framework out there, and working with it is a pleasure.

Small Agency

If you're working in a small agency, there are times where you want to save your money without degrading your customer websites' performances. Using a multi-tenant approach allows you to develop multiple websites reusing components, tests, CI/CD pipelines, and so on. It is also way cheaper to host a multi-tenant application on a single server than hosting 100 different websites on 100 other EC2/VPS instances. You have to scale just one server, and if you start to receive more traffic than expected, you have to configure only one CDN.

Big Corporate

Big corporates may also be interested in adopting a multi-tenant approach for their websites. Think of companies like IBM, Microsoft, or Adobe; they all have their design and component libraries. Every time they fix a bug or introduce any enhancement, they may want to deploy this new update directly on all of their websites. Well, using a multi-tenant approach, you only have to run one deployment task for updating hundreds of websites in just one move.

Caveats

There are some caveats you have to keep in mind when you're working with Krabs and Next.js.

You have to set up a custom server.
Krabs is an express.js middleware, so it requires a custom Express.js server to run. This will make Vercel deployments not available. Alternatives are DigitalOcean Apps, Heroku, or your custom server.

Common entry points
Both _document and _app pages will be common for all of your websites.