Vercel serveless

[raulfdm]

While trying to implement layerfig on my blog, I've realized that the way layerfig loads the file does not work for serverless.

That's because it expects the config/ files are there but even if we includeFiles all configs, it cannot resolve to that folder specifically.

Ideas

• check how it resolves file
• check for root path
• allow users to specify the entire root folder OR when configFolderPath is defined, only append the file name to this path
• create a dummy serverless project and host on vercel
  • add some random files
  • include those
  • console.log the folder structure

Resources

• https://vercel.com/guides/how-can-i-use-files-in-serverless-functions
• https://docs.astro.build/en/guides/integrations-guide/vercel/#includefiles

[raulfdm]

First analysis findings

I've realized that even by setting including files via includeFiles options it doesn't do the trick, but it's expected.

When we build for vercel for example, we have the following output:

.vercel
└── output
    ├── _functions
    ├── config.json
    ├── functions
    ├── server
    └── static

the folder functions contain all serverless functions for our application (this code is automatically generated by astro vercel's adapter) and it contains always the same folder structure:

.
├── ... other functions
├── _isr.prerender-config.json
└── _render.func
    ├── node_modules
    ├── package.json
    └── website

Because I'm building in a monorepo, we have this folder called website (the folder's name for this project in the monorepo). The files I've specified on includeFiles option, are listed there:

.vercel/output/functions/_isr.func/website
├── config
│   ├── base.yaml
│   ├── local.yaml
│   ├── preview.yaml
│   └── production.yaml
├── dist
│   └── server
├── node_modules
│   ├── prettier
│   └── zod
└── src
    └── pages

But of course, when it tries to resolve the files, it joins:

• process.cwd() (this will point to the root /var/task
• ./config => the default config folder path. Locally it works just fine
• base.json => file name

Producing the absolute path: /var/task/config/base.json.

However as mentioned above, this file doesn't exist. Instead, it should be /var/task/website/config/base.json.

Gotchas

__dirname

Vercel states:

We recommend using process.cwd() to determine the current directory of the Vercel Function instead of using __dirname. For example, this function reads the file users.json from the root of the repository.

https://vercel.com/guides/how-can-i-use-files-in-serverless-functions

When I try to log __dirname (ESM) in a route endpoint, I had this path:

/var/task/website/dist/server/pages/api/

/pages/api is where the function is located.

So we can't use it because we would need to know in advance how to navigate backwards until we reach config folder somewhere:

../ => /var/task/website/dist/server/pages
../../ => /var/task/website/dist/server
../../../ => /var/task/website/dist
../../../../ => /var/task/website
../../../../config => /var/task/website/

I don't think this is practical.

I still want to do more experiments including:

• Deploying on Netilfy and see if it's anyhow different
• Deploying from a single repo

But I managed to work this by checking if it's vercel and specifying a custom configFolder:

const config = new ConfigBuilder({
    validate(finalConfig) {
      return configSchema.parse(finalConfig);
    },
	// HERE
    configFolder: process.env.VERCEL_REGION ? 'website/config' : undefined,
  })

VERCEL_REGION is the only Vercel environment variable that's not present in Build time and that's very important. My config is also being used values for building, so if I point to an env var that's present on both build and runtime, the build will fail because the actual folder (when not running in the serverless) is config, not website/config.