... - Buildpacks — ContextQMD

+++ title="Making your application runnable" aliases=[ "/docs/buildpack-author-guide/create-buildpack/make-app-runnable" ] weight=5 +++

To make your app runnable, a default start command must be set. You'll need to add the following to the end of your build script:

bash

# ...

# Set default start command
cat > "${CNB_LAYERS_DIR}/launch.toml" << EOL
[[processes]]
type = "web"
command = ["node", "app.js"]
default = true
EOL

# ...

We also update our app.js to uncomment code to start the server:

const http = require('http');
 
const hostname = '0.0.0.0';
const port = 8080;
 
const server = http.createServer((req, res) => {
  res.statusCode = 200;
  res.setHeader('Content-Type', 'text/plain');
  res.end('Hello World!');
});

server.listen(port, hostname, () => {
  console.log(`Server running at http://${hostname}:${port}/`);
});

Your full node-js-buildpack/bin/build script should now look like the following:

bash

#!/usr/bin/env bash
set -eo pipefail

echo "---> NodeJS Buildpack"

# 1. CREATE THE LAYER DIRECTORY
node_js_layer="${CNB_LAYERS_DIR}"/node-js
mkdir -p "${node_js_layer}"

# 2. DOWNLOAD node-js
echo "---> Downloading and extracting NodeJS"
node_js_url=https://nodejs.org/dist/v18.18.1/node-v18.18.1-linux-x64.tar.xz
wget -q -O - "$node_js_url" | tar -xJf - --strip-components 1 -C "${node_js_layer}"

# 3. MAKE node-js AVAILABLE DURING LAUNCH
echo -e '[types]\nlaunch = true' > "${CNB_LAYERS_DIR}/node-js.toml"

# ========== ADDED ===========
# 4. SET DEFAULT START COMMAND
cat > "${CNB_LAYERS_DIR}/launch.toml" << EOL
[[processes]]
type = "web"
command = ["node", "app.js"]
default = true
EOL

Then rebuild your app using the updated buildpack:

bash

pack build test-node-js-app --path ./node-js-sample-app --buildpack ./node-js-buildpack

You should then be able to run your new NodeJS app:

bash

docker run --rm -p 8080:8080 test-node-js-app

and see the server log output:

text

Server running at http://0.0.0.0:8080/

Test it out by navigating to localhost:8080 in your favorite browser!

We can add multiple process types to a single app. We'll do that in the next section.