Guides

C++

In this guide we create and deploy a simple C++-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 example repository and cd into the examples/http-cpp/ directory:

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

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

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# 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:

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kraft cloud deploy -p 443:8080 .

The output shows the instance URL and other details:

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[●] Deployed successfully!
 │
 ├────────── name: http-cpp-jzbuo
 ├────────── uuid: b8e015fd-d006-49d5-849e-3fd497c9159a
 ├───────── state: running
 ├─────────── url: https://throbbing-wave-grxjih4t.fra0.kraft.host
 ├───────── image: http-cpp@sha256:a58873987104b52c13b79168a2e2f1a81876ba6efacd6dbc98e996afe5c09699
 ├───── boot time: 15.61 ms
 ├──────── memory: 128 MiB
 ├─────── service: throbbing-wave-grxjih4t
 ├── private fqdn: http-cpp-jzbuo.internal
 ├──── private ip: 172.16.6.5
 └────────── args: /http_server

In this case, the instance name is http-cpp-jzbuo and the URL is https://throbbing-wave-grxjih4t.fra0.kraft.host. They are different for each run.

Use curl to query the Unikraft Cloud instance of the C++ HTTP web server:

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curl https://throbbing-wave-grxjih4t.fra0.kraft.host

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Hello, World!

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

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kraft cloud instance list

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NAME                  FQDN                                      STATE    CREATED AT    IMAGE                                                           MEMORY   ARGS                            BOOT TIME
http-cpp-jzbuo        throbbing-wave-grxjih4t.fra0.kraft.host  running  1 minute ago  http-cpp@sha256:a58873987104b52c13b79168a2e2f1a81876ba6efac...  128 MiB  /http_server                    15614us

When done, you can remove the instance:

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kraft cloud instance remove http-cpp-jzbuo

Customize your Application

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

• http_server.cpp: the actual C++ HTTP server
• Kraftfile: the Unikraft Cloud specification
• Dockerfile: the Docker-specified application filesystem

Lines in the Kraftfile have the following roles:

• spec: v0.6: The current Kraftfile specification version is 0.6.

• runtime: base: The Unikraft runtime kernel to use is its base one.

• rootfs: ./Dockerfile: Build the application root filesystem using the Dockerfile.

• cmd: ["/http_server"]: Use /http_server as the starting command of the instance.

Lines in the Dockerfile have the following roles:

• FROM --platform=linux/x86_64 gcc:13.2.0-bookworm AS build: Build the filesystem from the bookworm gcc container image, to create a base image.

• COPY ./http_server.cpp /src/http_server.cpp: Copy the server implementation file (http_server.cpp) in the Docker filesystem (in /src/http_server.cpp).

The following options are available for customizing the application:

• If only updating the implementation in the http_server.cpp 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 C++ source files is added, update the cmd line in the Kraftfile and replace http_server.cpp 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:

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kraft cloud --help

Or visit the CLI Reference.