How do I reference dependencies in a layer in a custom runtime - Function Compute

In a custom runtime, Function Compute mounts layer contents under /opt but does not automatically add that path to the runtime's module search path. Unlike managed runtimes, custom runtimes do not include built-in path configuration, so you must register the layer directory with your runtime language — either through an environment variable or a code-level path call.

This page covers Python, Node.js, Java, and PHP.

How it works

When you attach a layer to a function, Function Compute extracts the layer's .zip file into /opt. The subdirectory depends on how you packaged the layer:

If you followed the Create a custom layer guide, the contents land in the default subdirectory for your language (for example, /opt/python).
If you used a custom directory name (for example, my-layer-code), the contents land in /opt/my-layer-code.

Use the actual directory path when configuring environment variables or setting the search path in code.

Quick reference

Language	Configuration method	Value
Python	`PYTHONPATH` environment variable	`/opt/python`
Python	`sys.path.append` in handler file	`/opt/python`
Node.js	`NODE_PATH` environment variable	`/opt/nodejs/node_modules`
Java	`-classpath` in startup command	`/code/:/opt/java/lib/*`
Java	`CLASSPATH` environment variable	`/code/:/opt/java/lib/*`
PHP	`set_include_path` in handler file	`/opt/php`

Python

Choose one of the following methods.

Method 1: Set the `PYTHONPATH` environment variable

Add the layer directory to the PYTHONPATH environment variable on your function:

PYTHONPATH=/opt/python

Method 2: Modify the handler file

Add the following lines at the top of your handler file, before any imports from the layer:

import sys
sys.path.append('/opt/python')
# import <PackageFromLayer>

For a working example, see python-demo-with-lib-in-layer.

Node.js

Set the NODE_PATH environment variable on your function:

NODE_PATH=/opt/nodejs/node_modules

For a working example, see nodejs-demo-with-lib-in-layer.

Java

Choose one of the following methods.

Method 1: Use `-classpath` in the startup command

Add /opt/java/lib/* to the -classpath parameter in your startup command:

java -Dserver.port=9000 -classpath /code/:/opt/java/lib/* com.example.demo.DemoApplication

Method 2: Set the `CLASSPATH` environment variable

Add the layer directory to the CLASSPATH environment variable on your function:

CLASSPATH=/code/:/opt/java/lib/*

Important

If you use CLASSPATH, do not use the -jar parameter to launch your application. When Java runs with -jar, the JVM reads the entry point from MANIFEST.MF and ignores all classpath settings from environment variables and command-line arguments. For example, the following command does not load the layer dependencies:

java -classpath ${CLASSPATH} -jar yourJarExe.jar

PHP

Add the following lines at the top of your handler file, before any imports from the layer:

<?php
$path = '/opt/php';
set_include_path(get_include_path() . PATH_SEPARATOR . $path);