Kubernetes Series Part 1 - Build an Express API

What We’ll Build

This will be the beginning of a Kubernetes series that will guide us through deploying a simple Node / Express application to a Kubernetes cluster on DigitalOcean.

Let’s build a simple Express application that queries a REST API. Instead of querying an API directly from you client-side application, we’ll build a small proxy API to stand in the middle of your frontend application and your backend API. Let’s use the OpenWeatherMap API for this project.

Prerequisites

Beginner knowledge of REST APIs
Some knowledge of Express (We won’t go into too much detail on the creation of the Express API)
Node (v17.5.0+) installed on your machine
OpenWeatherMap free account and API key

Get an OpenWeatherMap API Key

Head over to https://openweathermap.org/api and sign up for a free account. You’ll be given an API token to use.

Build the Express App

We’ll use the Express framework to build out our api. This framework will start a node server and allow us to create custom routes. Start out by creating a new directory for this project.

mkdir k8s-series && cd k8s-series

Express runs on a node server, so let’s initialize a new npm package for this project.

# yarn
yarn init -y

# npm
npm init -y

For this project, you need a few packages: express and dotenv, and nodemon.

# npm
npm install express dotenv
npm install -D nodemon

# yarn
yarn add express dotenv
yarn add nodemon -D

For nodemon to work, replace your start script in your package.json with this:

// package.json

"scripts": {
    "start": "nodemon index.js"
}

⚠️ node-fetch is included (experimentally) with node starting in version 17.5. If you are using an older version of node, either switch versions, or install node-fetch@2.6.7

Fetching the current weather for our zip code will require two calls to OpenWeather. The first is a call to the GeoLocation API which will turn our zip code into lat and lon. The second API call will fetch the current weather with the coordinates we receive.

Create a new file called index.js in the root of your project’s directory and add the following code.

// index.js

const express = require('express');
require('dotenv').config();
const app = express();
const PORT = 3000;

app.get('/', (req, res) => {
  res.send('Hello Weather');
});

// Get the weather for a zip code.
app.get('/weather/zip/:zip/:country?', async (req, res) => {
  // Get the zip from the params
  const { zip } = req.params;

  // If we have a country in the params, use it, else use 'US'
  const country = req.params.country || 'US';

  // Get the lat / lon for the zip
  let latLonRes = await fetch(
    `http://api.openweathermap.org/geo/1.0/zip?zip=${zip},${country}&appid=${process.env.WEATHER_API_KEY}`
  );
  const { lat, lon } = await latLonRes.json();

  // Get the weather for the lat / lon received from the previous request
  const weatherRes = await fetch(
    `https://api.openweathermap.org/data/2.5/weather?lat=${lat}&lon=${lon}&units=metric&appid=${process.env.WEATHER_API_KEY}`
  );
  const weatherJson = await weatherRes.json();

  // Return a 200 response with our weather data as JSON
  res.status(200).json({ data: weatherJson });
});

// Start the app on Port 3000
app.listen(PORT, () => {
  console.log(`Example app listening on port ${PORT}`);
});

⚠️ Do not commit your API key to github / version control! Create a .env file and store your API key there. We will learn how to deal with these ‘secrets’ in Kubernetes in a later article. Also, you will notice there’s no error handling in the example above. For the sake of simplicity, I left it out. I implore you to implement your own error handling if you would like to do that.

Start up your server with yarn start or npm run start. Head over to a browser and visit localhost:3000/weather/zip/90210. You should see the current weather for Beverly Hills as JSON in your browser window.

{
  "data": {
    "coord": { "lon": -118.4065, "lat": 34.0901 },
    "weather": [
      { "id": 800, "main": "Clear", "description": "clear sky", "icon": "01d" }
    ],
    "base": "stations",
    "main": {
      "temp": 15.93,
      "feels_like": 15.93,
      "temp_min": 13.97,
      "temp_max": 17.62,
      "pressure": 1010,
      "humidity": 90
    },
    "visibility": 10000,
    "wind": { "speed": 2.06, "deg": 230 },
    "clouds": { "all": 0 },
    "dt": 1665929250,
    "sys": {
      "type": 2,
      "id": 2012608,
      "country": "US",
      "sunrise": 1665928768,
      "sunset": 1665969509
    },
    "timezone": -25200,
    "id": 5328041,
    "name": "Beverly Hills",
    "cod": 200
  }
}

That’s It!

Next, we’ll look at containerizing this app with Docker.

I encourage you to play around with the API you just built. Check out the OpenWeather API docs and try to pass a city name instead of a zip code. If you’d like more detailed info, consider signing up for their 3.0 OneCall API. You get 1,000 calls a day for free, but you must give them your payment info, so be careful

Enjoy 😃

Kubernetes Series Part 1 - Build an Express API

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What We’ll Build

Prerequisites

Get an OpenWeatherMap API Key

Build the Express App

That’s It!

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Comments

More from this blog

What We’ll Build

Prerequisites

Get an OpenWeatherMap API Key

Build the Express App

That’s It!