next-build-id

Use a consistent, git-based build id for your Next.js app

Small package to generate a consistent, git-based build id for your Next.js app when running next build on each server in a multi-server deployment.

This module exports a function that you can use as your generateBuildId config option in next.config.js.

By default, it will use the latest git commit hash from the local git repository (equivalent of git rev-parse HEAD):

// next.config.js
const nextBuildId = require('next-build-id')
module.exports = {
  generateBuildId: () => nextBuildId({ dir: __dirname })
}
// => 'f9fc968afa249d162c924a8d5b4ce6562c164c2e'

If you'd rather use a build id relative to the most recent tag in your git repo, pass describe: true as an option and the output of git describe --tags will be used instead:

// next.config.js
const nextBuildId = require('next-build-id')
module.exports = {
  generateBuildId: () => nextBuildId({ dir: __dirname, describe: true })
}
// => 'v1.0.0' (no changes since v1.0.0 tag)
// => 'v1.0.0-19-ga8f7eee' (19 changes since v1.0.0 tag)

This module also exposes a synchronous version for custom needs, e.g. passing the build id directly to a Sentry configuration. Just call nextBuildId.sync({ dir: __dirname }) instead.

Why?

If you're running multiple instances of your app sitting behind a load balancer without session affinity (and you're building your app directly on each production server instead of pre-packaging it), a tool like this is necessary to avoid Next.js errors like "invalid build file hash", which happens when the same client (browser code) talks to multiple server backends (Node server) that have different build ids.

The build id used by your app is stored on the file system in a BUILD_ID text file in your build directory, which is .next by default.

Install

$ npm i next-build-id

API

This module exports two functions, one that is asynchronous (nextBuildId() primary export) and one that is synchronous (nextBuildId.sync()). Both functions accept a single options object, supporting the same options listed below. Both functions return (or resolve to) a string, representing the git-based build id.

The options supported are:

• dir (string, default process.cwd()): a directory within the local git repository

  Using __dirname from your next.config.js module is generally safe. The default value is assumed to be the directory from which you are running the next build command, but this may not be correct based on how you build your Next.js app.

• describe (boolean, default false): use git tag description instead of latest commit sha

  Specify this as true to use git describe --tags instead of git rev-parse HEAD for generating the build id. If there are no tags in your local git repository, the latest commit sha will be used instead, unless you also specify fallbackToSha: false.

• fallbackToSha (boolean, default true): fallback to latest commit sha when describe: true and no tags exist

  Only applies when using describe: true. If you want to be strict about requiring the use (and presence) of tags, then disable this with fallbackToSha: false, in which case an error will be thrown if no tags exist.

Note that this module really provides a generic way to get an id or status string for any local git repository, meaning it is not directly tied to Next.js in any way - it just depends on how you use it.

Reference

• zeit/next.js#786
• zeit/next.js#2978 (comment)
• zeit/next.js#3299 (comment)
• "Handle BUILD_ID Mismatch Error" on Next.js wiki

License

ISC © Andrew Goode