Run a Ruby app

In this guide we create and deploy a simple Ruby-based HTTP web server. To run this example, follow these steps:

1. Install the kraft CLI tool and a container runtime engine, e.g. Docker.

2. Clone the examples repository and cd into the examples/http-ruby3.2/ directory:

git clone https://github.com/kraftcloud/examples
cd examples/http-ruby3.2/

Make sure to log into KraftCloud by setting your token and a metro close to you. We use fra0 (Frankfurt, 🇩🇪) in this guide:

# Set KraftCloud access token
export KRAFTCLOUD_TOKEN=token
# Set metro to Frankfurt, DE
export KRAFTCLOUD_METRO=fra0

When done, invoke the following command to deploy this application on KraftCloud:

kraft cloud deploy -p 443:8080 -M 256 .

The output shows the instance URL and other details:

[●] Deployed successfully!
 │
 ├────────── name: http-ruby32-s6l8n
 ├────────── uuid: b1ebbbc0-5efa-476c-adb6-99866773245c
 ├───────── state: running
 ├─────────── url: https://silent-resonance-1jtz5c66.fra0.kraft.host
 ├───────── image: http-ruby32@sha256:4cf3b341898e6ebff18ff2b68353ef872dded650c9d16a6f005a8fbe8a7cbb3d
 ├───── boot time: 71.19 ms
 ├──────── memory: 256 MiB
 ├─ service group: silent-resonance-1jtz5c66
 ├── private fqdn: http-ruby32-s6l8n.internal
 ├──── private ip: 172.16.3.3
 └────────── args: /usr/bin/ruby /src/server.rb

In this case, the instance name is http-ruby32-s6l8n and the URL is https://silent-resonance-1jtz5c66.fra0.kraft.host. They are different for each run.

Use curl to query the KraftCloud instance of the Ruby-based HTTP web server:

curl https://silent-resonance-1jtz5c66.fra0.kraft.host

Hello, World!

At any point in time, you can list information about the instance:

kraft cloud instance list

NAME               FQDN                                        STATE    CREATED AT      IMAGE                                                                    MEMORY   ARGS                          BOOT TIME
http-ruby32-s6l8n  silent-resonance-1jtz5c66.fra0.kraft.host  running  12 minutes ago  razvan.unikraft.io/http-ruby32@sha256:4cf3b341898e6ebff18ff2b68353ef...  256 MiB  /usr/bin/ruby /src/server.rb  71191us

When done, you can remove the instance:

kraft cloud instance remove http-ruby32-s6l8n

Customize your Application

To customize the application, update the files in the repository, listed below:

• server.rb: the actual Ruby HTTP server
• Kraftfile: the KraftCloud specification
• Dockerfile: the Docker-specified application filesystem

server.rb

require 'socket'

socket = TCPServer.new(8080)

loop do
  client = socket.accept

  request = client.gets

  response = "HTTP/1.1 200 OK\r\n" \
    "Content-type: text/html\r\n" \
    "Connection: close\r\n" \
    "\r\n" \
    "Hello, World!"
  client.puts(response)

  client.close
end

Kraftfile

spec: v0.6

runtime: ruby:3.2

rootfs: ./Dockerfile

cmd: ["/usr/bin/ruby", "/src/server.rb"]

Dockerfile

FROM scratch

# Simple Ruby HTTP server
COPY ./server.rb /src/server.rb

The following options are available for customizing the application:

• If only updating the implementation in the server.rb source file, no other change is required.

• If new files are added, these have to be copied in the application filesystem, using the COPY command in the Dockerfile.

• If a new Ruby source files is added, update the cmd line in the Kraftfile and replace server.rb to run that file when creating the instance.

• More extensive changes may require expanding the Dockerfile with additional Dockerfile commands.

Learn More

Use the --help option for detailed information on using KraftCloud:

kraft cloud --help

Or visit the CLI Reference.