Heroku Node.js Support
Last updated May 18, 2023
Table of Contents
This document describes the general behavior of Heroku as it relates to the recognition and execution of Node.js applications. For a more detailed explanation of how to deploy an application, see Getting Started with Node.js on Heroku.
Activation
The Heroku Node.js buildpack is employed when the application has a
package.json
file in the root directory.
Node.js Runtimes
Node versions adhere to semver, the semantic versioning convention popularized by GitHub. Semver uses a version scheme in the form MAJOR.MINOR.PATCH
.
MAJOR
denotes incompatible API changesMINOR
denotes added functionality in a backwards-compatible mannerPATCH
denotes backwards-compatible bug fixes
Supported Runtimes
Heroku supports the Current version of Node.js as well as all Active LTS (Long-Term-Support) versions. Heroku will support new releases within 24 hours of the official release from the Node team. As illustrated by the Node.js release schedule below, Heroku’s currently supported Node.js versions are 16.x
, 18.x
, and 20.x
.
Other Available Runtimes
Since Heroku is based on a standard Ubuntu Linux stack, you can run most Node versions (>= 0.10.0
) on the platform. However, the testing and support focus of the buildpack will be oriented around active LTS and Stable releases.
Specifying a Node.js Version
Always specify a Node.js version that matches the runtime you’re developing and testing with. To find your version locally:
$ node --version
v18.7.0
First, ensure that your application is using the heroku/nodejs
buildpack:
$ heroku buildpacks
=== issuetriage Buildpack URLs
1. heroku/nodejs
Now, use the engines
section of the package.json
to specify the version of Node.js to use on Heroku. Drop the ‘v’ to save only the version number:
{
"name": "example-app",
"description": "a really cool app",
"version": "1.0.0",
"engines": {
"node": "18.x"
}
}
If a Node version isn’t specified in the engines
section, Node.js 18.x
will automatically be used.
It’s recommended to use an x
in the patch to get the latest patch updates from Node. You can also specify a minor range such as 18.7
or an exact version, like 16.19.1
.
Because Node does regular security releases on all supported major versions, it’s recommended to specify a major range (eg, 18.x
) to get security updates automatically.
Specifying an npm Version
Node.js comes bundled with npm, so most of the time you don’t need to specify a separate npm version. However, if you intentionally use a different version of npm locally, you can specify the same version of npm on Heroku:
{
"name": "example-app",
"description": "a really cool app",
"version": "0.0.1",
"engines": {
"npm": "7.x"
}
}
Specifying a Yarn Version
If you have a yarn.lock
file at the root of your application along with package.json
, Heroku downloads and installs Yarn, which is used to install your dependencies. Specify the version you are using locally so that Heroku uses the same version.
{
"name": "example-app",
"description": "a really cool app",
"version": "1.0.0",
"engines": {
"yarn": "1.x"
}
}
Build Behavior
Node projects are built with either the Yarn package manager or with the npm package manager.
If a yarn.lock
file is detected in the root of the project, yarn is used for installing dependencies and running scripts. Otherwise, npm is used. If you have yarn.lock
checked into your project, but still want to use npm to build on Heroku, just add yarn.lock
to your .slugignore file.
Package Installation
By default, Heroku will install all dependencies listed in package.json
under dependencies
and devDependencies
.
After running the installation and build steps
Heroku will strip out the packages declared under devDependencies
before deploying the application.
Heroku uses the lockfiles, either the package-lock.json
or yarn.lock
, to install the expected dependency tree, so be sure to check those files into git to ensure the same dependency versions across environments. If you are using npm, Heroku will use npm ci
to set up the build environment.
Using npm install
If you’d rather use npm install
instead of npm ci
to create the build environment, you can use the USE_NPM_INSTALL
environment variable to let the buildpack know. You can do this by running:
$ heroku config:set USE_NPM_INSTALL=true
If you use npm install
, you will want to use your Heroku cache to speed up your build times. If you’re not using npm install
, you can go ahead and disable the build cache.
$ heroku config:set NODE_MODULES_CACHE=false
Only installing dependencies
You can direct Heroku to only install dependencies
by
setting the following environment variables:
NPM_CONFIG_PRODUCTION=true
for npmYARN_PRODUCTION=true
for Yarn v1
$ heroku config:set NPM_CONFIG_PRODUCTION=true YARN_PRODUCTION=true
Skip pruning
If you need access to packages declared under devDependencies
in a different buildpack or at runtime then,
depending on the package manager used, you can set one of the following
environment variables to skip the pruning step:
NPM_CONFIG_PRODUCTION=false
for npmYARN_PRODUCTION=false
for Yarn v1YARN2_SKIP_PRUNING=true
for Yarn v2+
$ heroku config:set NPM_CONFIG_PRODUCTION=false YARN_PRODUCTION=false YARN2_SKIP_PRUNING=true
NODE_ENV
is not production
By default NODE_ENV
is set to production
. If NODE_ENV
is any other value, the pruning step will be skipped.
$ git push heroku main
...
-----> Pruning devDependencies
Skipping because NODE_ENV is 'test'
...
Check in all the created artifacts into git with the other files that have been generated to use Yarn in the .yarn
file.
Customizing the build process
If your app has a build step that you’d like to run when you deploy, you can use
a build
script in package.json:
"scripts": {
"start": "node index.js",
"build": "webpack"
}
If the package.json has a build
script that needs to be customized for Heroku, define a heroku-postbuild
script, which will run instead of the build
script.
"scripts": {
"start": "node index.js",
"build": "ng build",
"heroku-postbuild": "ng build --prod" // this will be run on Heroku
}
If a heroku-postbuild
script is specified, the build
script will not run.
Heroku-specific build steps
While npm install
and yarn install
have standard preinstall
and postinstall
scripts, you may want to run scripts only before or after other Heroku build steps. For instance, you may need to configure npm, git, or ssh before Heroku installs dependencies, or you may need to build production assets after dependencies are installed.
For Heroku-specific actions, use the heroku-prebuild
, heroku-postbuild
, and heroku-cleanup
scripts:
"scripts": {
"heroku-prebuild": "echo This runs before Heroku installs dependencies.",
"heroku-postbuild": "echo This runs after Heroku installs dependencies, but before Heroku prunes and caches dependencies.",
"heroku-cleanup": "echo This runs after Heroku prunes and caches dependencies."
}
Environment variables
Your app’s environment is available during the build, allowing you to adjust build behavior based on the values of environment variables. For instance:
$ heroku config:set MY_CUSTOM_VALUE=foobar
Build flags
If your app is running a build step, make sure that it is used for development and production. If it’s not, then use the build flag environment variable to set flags for the build script. For instance, if your build step is:
"scripts": {
"build": "ng build"
}
You can set the NODE_BUILD_FLAGS
environment variable:
$ heroku config:set NODE_BUILD_FLAGS="--prod"
Setting this variable will run ng build --prod
in the build step instead.
Configuring npm
npm
reads configuration from any environment variables beginning with NPM_CONFIG
.
You can also control npm’s behavior via a .npmrc
file in your project’s root.
When NPM_CONFIG_PRODUCTION is true, npm automatically runs all scripts in a subshell where NODE_ENV is ‘production.’
Private Dependencies
If pulling from a private dependency source, such as NPM Enterprise or Gemfury, the project will need to configure an alternate registry with access tokens.
Add the private registry url to the .npmrc
. In this case, we’ll specify npm‘s registry even though its public. The scope should be replaced with the scope that is used for the private module in the registry. Then, add the registry url that will point to using the auth token.
echo "@scope:registry=https://registry.npmjs.org" >> .npmrc
echo -e "//registry.npmjs.org/:_authToken=\${NPM_TOKEN}" >> .npmrc
This registry url is specific to the npm registry, but other private package registries may have similar urls. Consult with the documentation of the private registry.
The .npmrc
should look like this:
@scope:registry=https://registry.npmjs.org
//registry.npmjs.org/:_authToken=${NPM_TOKEN}
Make sure the NPM_TOKEN
has been added to the Heroku config, so that the build can access the token and install the private package.
heroku config:set NPM_TOKEN=PRIVATE_NPM_TOKEN
Customize Binary Downloads
You can customize where Node and yarn binaries are downloaded by setting environment variables NODE_BINARY_URL
and YARN_BINARY_URL
to a custom URL. For instance:
$ heroku config:set NODE_BINARY_URL=https://s3.amazonaws.com/your-custom-binary-url/
Cache behavior
Heroku maintains a build cache that is persisted between builds. This cache is used to store caches for npm, yarn, and bower.
You can disable all caching for Node.js apps if you prefer:
$ heroku config:set NODE_MODULES_CACHE=false
$ git commit -am 'disable node_modules cache' --allow-empty
$ git push heroku main
Custom caching
Heroku stores the node_modules
and bower_components
directories by default. You can override these defaults by providing a cacheDirectories
array in your top-level package.json.
For example, if you build inside client and server sub-directories:
"cacheDirectories": ["client/node_modules", "server/node_modules"]
Or perhaps your app needs a large dictionary of some sort, stored in data/dictionary.txt:
"cacheDirectories": ["data"]
Runtime behavior
The buildpack puts node
, npm
, and node_modules/.bin
on the PATH
so they can be executed with heroku run or used directly in a Procfile:
$ cat Procfile
web: npm start
The NODE_ENV
environment variable is set to ‘production’ by default, but you can set it to any arbitrary string:
$ heroku config:set NODE_ENV=staging
Usually, NODE_ENV should be ‘production.’ Several modules, including express, implicitly change their behavior based on NODE_ENV.
Default web process type
First, Heroku looks for a Procfile specifying your process types.
If no Procfile
is present in the root directory of your app during the build process, your web process will be started by running npm start
, a script you can specify in package.json, eg:
"scripts": {
"start": "node server.js"
}
If you only want to run non-web
processes in your app’s formation, you’ll need to explicitly scale web
down and the other process types up. For example:
$ heroku scale web=0 worker=1
Warnings
If a build fails, the Node.js Buildpack identifies common issues in Node applications and provides warnings with best-practice recommendations. If you’re experiencing Node.js build issues, this is a good place to start debugging.
We also maintain a document to help troubleshoot common Node.js issues.
Add-ons
No add-ons are provisioned by default. If you need a database for your app, add one explicitly:
$ heroku addons:create heroku-postgresql
Multi-buildpack behavior
When using the Node.js Buildpack with other buildpacks, it automatically exports the node
, npm
, and node_modules
binaries onto the PATH
for subsequent buildpacks to consume.
Going further
The Heroku Node.js buildpack is open source. For a better technical understanding of how the buildpack works, check out the source code at github.com/heroku/heroku-buildpack-nodejs.