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title: Tips for Node.js Applications
owner: Buildpacks
<strong><%= modified_date %></strong>
This topic provides Node-specific information to supplement the general guidelines in the [Deploy an Application](../../devguide/deploy-apps/deploy-app.html) topic.
## <a id='buildpack'></a> About the Node.js Buildpack ##
For information about using and extending the Node.js buildpack in Cloud
Foundry, see the [nodejs-buildpack repository]( in GitHub.
You can find current information about this buildpack on the Node.js buildpack [release page]( in GitHub.
The buildpack uses a default Node.js version. To specify the versions of Node.js and npm an app requires, edit the app's `package.json`, as described in "node.js and npm versions" in the [nodejs-buildpack repository](
## <a id='packagejson'></a> Application Package File ##
Cloud Foundry expects a `package.json` in your Node.js app.
You can specify the version of Node.js you want to use in the `engine` node of
your `package.json` file.
In general, Cloud Foundry supports the two most recent versions of Node.js.
See the GitHub [Node.js buildpack page]( for current information.
Example `package.json` file:
"name": "first",
"version": "0.0.1",
"author": "Demo",
"dependencies": {
"express": "3.4.8",
"consolidate": "0.10.0",
"swig": "1.3.2"
"engines": {
"node": "0.12.7",
"npm": "2.7.4"
## <a id='port'></a> Application Port ##
You must use the PORT environment variable to determine which port your
app should listen on. To also run your app locally, set the default port as `3000`.
app.listen(process.env.PORT || 3000);
## <a id='memory'></a> Low Memory Environments ##
When running node apps, you might notice that instances are occasionally
restarted due to memory constraints. Node does not know how much memory it is
allowed to use, and thus sometimes allows the garbage collector to wait past
the allowed amount of memory. To resolve this issue, set the `OPTIMIZE_MEMORY` environment variable to `true` (requires node v6.12.0 or greater). This sets `max_old_space_size` based on the available memory in the instance.
<pre class="terminal">
$ cf set-env my-app OPTIMIZE_MEMORY true
## <a id='start'></a> Application Start Command ##
Node.js apps require a start command.
You can specify the web start command for a Node.js app in a Procfile or in the app deployment manifest. For more information about Procfiles, see the [Configuring a Production Server](../prod-server.html) topic.
The first time you deploy, you are asked if you want to save your configuration.
This saves a `manifest.yml` in your app with the settings you
entered during the initial push.
Edit the `manifest.yml` file and create a start command as follows:
- name: my-app
command: node my-app.js
... the rest of your settings ...
Alternately, specify the start command with `cf push -c`.
<pre class="terminal">
$ cf push my-app -c "node my-app.js"
## <a id='nodemodules'></a> Application Bundling ##
You do not need to run `npm install` before deploying your app.
Cloud Foundry runs it for you when your app is pushed.
You can, if you prefer, run `npm install` and create a `node_modules` folder
inside of your app.
## <a id='discovery'></a> Solve Discovery Problems ##
If Cloud Foundry does not automatically detect that your app is a Node.js app, you can override auto-detection by specifying the Node.js buildpack.
Add the buildpack into your `manifest.yml` and re-run `cf push` with your
- name: my-app
... the rest of your settings ...
Alternately, specify the buildpack on the command line with `cf push -b`:
<pre class="terminal">
$ cf push my-app -b
## <a id='services'></a> Bind Services ##
Refer to [Configure Service Connections for Node.js](./node-service-bindings.html).
## <a id='env-var'></a>Environment Variables ##
You can access environments variable programmatically.
For example, you can obtain `VCAP_SERVICES` as follows:
Environment variables available to you include both those [defined by the system](../../devguide/deploy-apps/environment-variable.html#app-system-env)
and those defined by the Node.js buildpack, as described below.
### <a id='BUILD-DIR'></a>BUILD_DIR ###
Directory into which Node.js is copied each time a Node.js app is run.
### <a id='CACHE-DIR'></a>CACHE_DIR ###
Directory that Node.js uses for caching.
### <a id='PATH'></a>PATH ###
The system path used by Node.js.