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Unikraft Cloud

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:

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

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

Terminal window
# Set Unikraft Cloud access token
export UKC_TOKEN=token
# Set metro to Frankfurt, DE
export UKC_METRO=fra0

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

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

The output shows the instance URL and other details:

Terminal window
[●] 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: 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 Unikraft Cloud instance of the Ruby-based HTTP web server:

Terminal window
curl https://silent-resonance-1jtz5c66.fra0.kraft.host
Hello, World!

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

Terminal window
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  http-ruby32@sha256:4cf3b341898e6ebff18ff2b68353ef...  256 MiB  /usr/bin/ruby /src/server.rb  71191us

When done, you can remove the instance:

Terminal window
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 Unikraft Cloud specification
  • Dockerfile: the Docker-specified application filesystem
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

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 Unikraft Cloud:

Terminal window
kraft cloud --help

Or visit the CLI Reference.