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Guides

SSH and HTTP Server with C and Debugging Tools

This guide explains how to create and deploy a C app with debugging enabled. To run this example, follow these steps:

1. Install the CLI and a container runtime engine, for example Docker. Use the unikraft CLI or the legacy kraft CLI.

2. Clone the examples repository and cd into the examples/httpserver-c-debug directory:

Code
git clone https://github.com/unikraft-cloud/examples
cd examples/httpserver-c-debug/

Make sure to log into Unikraft Cloud and pick a metro close to you. This guide uses fra (Frankfurt, 🇩🇪):

For extensive debug information with strace, add the USE_STRACE=1 environment variable to the deploy command:

The output shows the instance address and other details:

Code
[●] Deployed successfully!
 │
 ├────── name: httpserver-c-debug-5pvem
 ├────── uuid: 08629a94-e2b1-466e-abb9-15ce46411b66
 ├───── metro: https://api.fra.unikraft.cloud/v1
 ├───── state: running
 ├──── domain: https://patient-snow-zdzhdy8r.fra.unikraft.app
 ├───── image: httpserver-c-debug@sha256:b24b95e236c8eff69615dd4f5d257beed5ee4047fd98d1b6fb200f89c63fa54c
 ├─ boot time: 66.56 ms
 ├──── memory: 256 MiB
 ├─── service: patient-snow-zdzhdy8r
 ├ private ip: 10.0.0.109
 └────── args: /usr/bin/wrapper.sh

In this case, the instance name is httpserver-c-debug-5pvem and the address is patient-snow-zdzhdy8r.fra.unikraft.app. They're different for each run.

Use curl to query the Unikraft Cloud instance:

Code
curl https://patient-snow-zdzhdy8r.fra.unikraft.app

Code
Hello, World!

For SSH, you need to set up a tunnel that handles the TLS connection to the Unikraft Cloud instance. This way, you have a non-TLS port that your SSH client can connect to:

Code
socat TCP-LISTEN:2222,reuseaddr,fork OPENSSL:patient-snow-zdzhdy8r.fra.unikraft.app:2222,verify=0

Then connect to the instance via SSH using:

Code
ssh -l root localhost -p 2222

You might see warnings like REMOTE HOST IDENTIFICATION HAS CHANGED. This is normal if you have set up tunnels to connect with SSH on localhost, so don't worry.

You can list information about the instance by running:

Code
NAME                      FQDN                                    STATE    STATUS       IMAGE                            MEMORY   VCPUS  ARGS                 BOOT TIME
httpserver-c-debug-5pvem  patient-snow-zdzhdy8r.fra.unikraft.app  running  since 4mins  httpserver-c-debug@sha256:b2...  256 MiB  1      /usr/bin/wrapper.sh  66.56 ms

When done, you can remove the instance:

Learn more

Use the --help option for detailed information on using Unikraft Cloud:

Or visit the CLI Reference or the legacy CLI Reference.