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:
# ...
# Set default start command
cat > "$layersdir/launch.toml" << EOL
[[processes]]
type = "web"
command = "bundle exec ruby app.rb"
default = true
EOL
# ...
Your full ruby-buildpack/bin/build script should now look like the following:
#!/usr/bin/env bash
set -eo pipefail
echo "---> Ruby Buildpack"
# 1. GET ARGS
layersdir=$1
# 2. CREATE THE LAYER DIRECTORY
rubylayer="$layersdir"/ruby
mkdir -p "$rubylayer"
# 3. DOWNLOAD RUBY
echo "---> Downloading and extracting Ruby"
ruby_url=https://s3-external-1.amazonaws.com/heroku-buildpack-ruby/heroku-22/ruby-3.1.3.tgz
wget -q -O - "$ruby_url" | tar -xzf - -C "$rubylayer"
# 4. MAKE RUBY AVAILABLE DURING LAUNCH
echo -e '[types]\nlaunch = true' > "$layersdir/ruby.toml"
# 5. MAKE RUBY AVAILABLE TO THIS SCRIPT
export PATH="$rubylayer"/bin:$PATH
export LD_LIBRARY_PATH=${LD_LIBRARY_PATH:+${LD_LIBRARY_PATH}:}"$rubylayer/lib"
# 6. INSTALL GEMS
echo "---> Installing gems"
bundle install
# ========== ADDED ===========
# 7. SET DEFAULT START COMMAND
cat > "$layersdir/launch.toml" << EOL
[[processes]]
type = "web"
command = "bundle exec ruby app.rb"
default = true
EOL
Then rebuild your app using the updated buildpack:
pack build test-ruby-app --path ./ruby-sample-app --buildpack ./ruby-buildpack
You should then be able to run your new Ruby app:
docker run --rm -p 8080:8080 test-ruby-app
and see the server log output:
[2019-04-02 18:04:48] INFO WEBrick 1.4.2
[2019-04-02 18:04:48] INFO ruby 2.5.1 (2018-03-29) [x86_64-linux]
== Sinatra (v2.0.5) has taken the stage on 8080 for development with backup from WEBrick
[2019-04-02 18:04:48] INFO WEBrick::HTTPServer#start: pid=1 port=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.