Demo Env file

In this lesson you will reproduce and fix a common problem that occurs when using Telepresence to intercept a Kubernetes deployment: your locally running process fails because a pod environment variable containing the inventory service URL (API_URL) is not present on your workstation. This guide walks through the failure scenario, explains why it happens, and shows how to export pod environment variables with Telepresence into a .env file and consume them locally with dotenv.

Problem overview

The Kubernetes Deployment sets API_URL in the container environment to point at the in-cluster inventory service.
When you create a Telepresence intercept and run the application locally, those pod environment variables are not automatically available to the local process.
The local process then attempts to call the inventory service with an undefined URL and throws ERR_INVALID_URL.

Example error when API_URL is undefined:

Error [ERR_INVALID_URL]: Invalid URL: undefined?product_ids=1,2,3
    at onParseError (internal/url.js:263:9)
    at new URL (internal/url.js:339:5)
    ...
{
  code: 'ERR_INVALID_URL',
  input: 'undefined?product_ids=1,2,3'
}

Reproducing snippet that fails when apiURL is undefined:

const products = [];

app.get("/", async (req, res) => {
  try {
    const productIds = req.query.product_ids;
    console.log(productIds);
    const idsArray = productIds.split(",").map((id) => parseInt(id.trim(), 10));
    console.log(idsArray);
    const filteredProducts = products.filter((product) =>
      idsArray.includes(product.id)
    );
    console.log(filteredProducts);

    // If apiURL is undefined, this fetch will throw ERR_INVALID_URL
    const response = await fetch(`${apiURL}?product_ids=${idsArray.join(",")}`);
    if (!response.ok) {
      throw new Error(`HTTP error! Status: ${response.status}`);
    }
    const inventory = await response.json();
    // ... respond with combined product + inventory data
  } catch (err) {
    console.error(err);
    res.status(500).send(err.message);
  }
});

Note: the snippet above references apiURL directly; unless you set apiURL from process.env.API_URL the variable will be undefined and the request URL will be invalid.

Deployment manifest example (shows API_URL set in the pod)

spec:
  template:
    spec:
      containers:
      - name: products
        volumeMounts:
        - name: db-config
          mountPath: /tmp
        ports:
        - containerPort: 3000
          name: web
        env:
        - name: "API_URL"
          value: "http://inventory-service:3000/"
---
apiVersion: v1
kind: Service
metadata:
  name: products-service
spec:
  type: LoadBalancer

Why it fails when intercepting

The Deployment configures API_URL for the container when running in-cluster.
Telepresence intercepts by stopping the real pod traffic and routing traffic to your workstation. It does not automatically inject the pod’s environment variables into your shell.
Your local process therefore does not have the same environment (internal DNS names, service ports), causing service calls to fail.

Solution overview

Use Telepresence’s --env-file option to export the pod environment to a file (commonly named .env), then load that file into your local Node.js process with a library such as dotenv. This ensures your local process sees the same values (for example, API_URL) as the in-cluster pod.

Step-by-step reproduction and fix

Make sure there’s no existing intercept for the workload:

telepresence list
telepresence leave products-depl

Create an intercept and ask Telepresence to write the pod’s environment to a file (by convention .env):

telepresence intercept products-depl -p 8000 --env-file .env

Sample Telepresence output:

Using Deployment products-depl
    Intercept name          : products-depl
    State                   : ACTIVE
    Workload kind           : Deployment
    Destination             : 127.0.0.1:8000
    Service Port Identifier : 3000/TCP
    Volume Mount Point      : /tmp/telfs-3110725221
    Intercepting            : all TCP connections

Telepresence will create the .env file in your current directory. It contains all the pod environment variables, for example:

API_URL=http://inventory-service:3000/
AUTH_SERVICE_PORT=tcp://10.100.10.52:3000
AUTH_SERVICE_PORT_3000_TCP=tcp://10.100.10.52:3000
AUTH_SERVICE_PORT_3000_TCP_ADDR=10.100.10.52
AUTH_SERVICE_PORT_3000_TCP_PORT=3000
AUTH_SERVICE_PORT_3000_TCP_PROTO=tcp
AUTH_SERVICE_SERVICE_HOST=10.100.10.52
AUTH_SERVICE_SERVICE_PORT=3000
A_TELEPRESENCE_MOUNTS=/tmp:/var/run/secrets/kubernetes.io/serviceaccount
INVENTORY_SERVICE_PORT=tcp://10.100.246.69:3000
INVENTORY_SERVICE_PORT_3000_TCP=tcp://10.100.246.69:3000
INVENTORY_SERVICE_PORT_3000_TCP_ADDR=10.100.246.69
INVENTORY_SERVICE_PORT_3000_TCP_PORT=3000
INVENTORY_SERVICE_PORT_3000_TCP_PROTO=tcp
INVENTORY_SERVICE_SERVICE_HOST=10.100.246.69
INVENTORY_SERVICE_SERVICE_PORT=3000
KUBERNETES_PORT=tcp://10.100.0.1:443
KUBERNETES_PORT_443_TCP=tcp://10.100.0.1:443
KUBERNETES_PORT_443_TCP_ADDR=10.100.0.1

Update your local Node.js application to load .env and override any existing environment variables so the local process uses the same values as the pod.

Example Express server that uses dotenv and reads API_URL from process.env:

// Load environment variables from .env and override any existing values
require('dotenv').config({ override: true });

const express = require("express");
const app = express();
const port = 8000;

// Ensure we use the environment variable provided by Telepresence (.env)
const apiURL = process.env.API_URL;
console.log("API_URL:", apiURL);

const products = [
  {
    id: 1,
    name: "iphone 14",
    price: 900,
    category: "electronics",
    onSale: false
  },
  {
    id: 2,
    name: "pixel 7",
    price: 600,
    category: "electronics",
    onSale: true
  }
];

app.get("/", async (req, res) => {
  try {
    const productIds = req.query.product_ids || '';
    const idsArray = productIds
      .split(",")
      .map((id) => parseInt(id.trim(), 10))
      .filter(Number.isFinite);

    const filteredProducts = products.filter((product) =>
      idsArray.includes(product.id)
    );

    // apiURL should now be defined from process.env.API_URL
    const response = await fetch(`${apiURL}?product_ids=${idsArray.join(",")}`);
    if (!response.ok) {
      throw new Error(`HTTP error! Status: ${response.status}`);
    }
    const inventory = await response.json();

    res.json({
      products: filteredProducts,
      inventory
    });
  } catch (err) {
    console.error(err);
    res.status(500).send(err.message);
  }
});

app.listen(port, () => {
  console.log(`Products service listening at http://localhost:${port}`);
});

Once you have the .env file created by Telepresence and you run your local server with the code above, requests that require the inventory service should succeed because API_URL is now defined as it was in-cluster.

Node runtime note: The example uses global fetch — available in Node 18+. If you are on an older Node version, install and import node-fetch (or upgrade Node) before using fetch.

Quick reference: Telepresence commands and files

Purpose	Command / File	Notes
List current intercepts	`telepresence list`	Shows active intercepts and statuses
Remove an intercept	`telepresence leave products-depl`	Replace `products-depl` with your intercept name
Create intercept and export pod env	`telepresence intercept products-depl -p 8000 --env-file .env`	`--env-file` writes pod env vars to `.env`
Local env file	`.env`	Contains `API_URL` and other in-cluster env values; do not commit

Summary

The Deployment configured API_URL in the pod, but when you intercept and run locally you must provide those same environment variables on your workstation.
Telepresence’s --env-file option extracts pod environment variables to a file (commonly .env).
Use a library such as dotenv to load that file into your local process so the local behavior matches the in-cluster environment.

Add your .env file to .gitignore and avoid committing it. The .env file may contain internal IPs and service endpoints that should not be checked into source control.

Links and references

Telepresence (official project): https://www.telepresence.io/
Telepresence docs: https://www.telepresence.io/docs/
dotenv npm package: https://www.npmjs.com/package/dotenv
Kubernetes documentation: https://kubernetes.io/docs/

Course Introduction

Telepresence For Kubernetes

Problem overview

Deployment manifest example (shows API_URL set in the pod)

Why it fails when intercepting

Solution overview

Step-by-step reproduction and fix

Quick reference: Telepresence commands and files

Summary

Links and references

Watch Video

​Problem overview

​Deployment manifest example (shows API_URL set in the pod)

​Why it fails when intercepting

​Solution overview

​Step-by-step reproduction and fix

​Quick reference: Telepresence commands and files

​Summary

​Links and references

Watch Video

Problem overview

Deployment manifest example (shows API_URL set in the pod)

Why it fails when intercepting

Solution overview

Step-by-step reproduction and fix

Quick reference: Telepresence commands and files

Summary

Links and references