# SSH and HTTP Server with C and Debugging Tools

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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.
   Use the [unikraft CLI](/cli/unikraft) or the legacy [kraft CLI](https://unikraft.org/docs/cli/install).
   You need a [BuildKit](https://github.com/moby/buildkit) builder. The easiest way to get one is via [Docker](https://docs.docker.com/engine/install/).
   Alternatively, you can also directly set up and use BuildKit, see the [quick start](https://github.com/moby/buildkit#quick-start).

:::note
The unikraft CLI is the current standard, while kraft is the legacy version.
Choose one of the CLIs below and only run the commands associated with it for the rest of this guide.
:::

2. Clone the [`examples` repository](https://github.com/unikraft-cloud/examples) and `cd` into the `examples/httpserver-c-debug` directory:

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

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

<CodeTabs syncKey="cli">

```bash title="unikraft"
unikraft login
```

```bash title="kraft"
# Set Unikraft Cloud access token
export UKC_TOKEN=token
# Set metro to Frankfurt, DE
export UKC_METRO=fra
```

</CodeTabs>

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

<CodeTabs syncKey="cli">

```bash title="unikraft"
unikraft build . --output <my-org>/httpserver-c-debug:latest
unikraft run --scale-to-zero policy=off --metro fra -p 443:8080/tls+http -p 2222:2222/tls -e PUBKEY=.... -e USE_STRACE=1 -m 256M --image <my-org>/httpserver-c-debug:latest
```

```bash title="kraft"
kraft cloud deploy --scale-to-zero off -p 443:8080/tls+http -p 2222:2222/tls -M 256Mi -e PUBKEY="...." -e USE_STRACE=1 .
```

</CodeTabs>

The output shows the instance address and other details:

<CodeTabs syncKey="cli">

```ansi title="unikraft"
metro:        fra
name:         httpserver-c-debug-5pvem
uuid:         08629a94-e2b1-466e-abb9-15ce46411b66
state:        starting
image:        <my-org>/httpserver-c-debug
resources:
  memory:     256MiB
  vcpus:      1
service:
  uuid:       2e016406-0c59-4d74-6deb-fdcb206fdb1e
  name:       patient-snow-zdzhdy8r
  domains:
  - fqdn:     patient-snow-zdzhdy8r.fra.unikraft.app
networks:
- uuid:       80a11393-8eca-ec11-3028-fb8908b21894
  private-ip: 10.0.0.109
  mac:        12:b0:45:b3:18:b2
timestamps:
  created:    just now
```

```ansi title="kraft"
[●] Deployed successfully!
 │
 ├───────── name: httpserver-c-debug-5pvem
 ├───────── uuid: 08629a94-e2b1-466e-abb9-15ce46411b66
 ├──────── metro: https://api.fra.unikraft.cloud/v1
 ├──────── state: starting
 ├─────── domain: https://patient-snow-zdzhdy8r.fra.unikraft.app
 ├──────── image: oci://unikraft.io/<my-org>/httpserver-c-debug@sha256:b24b95e236c8eff69615dd4f5d257beed5ee4047fd98d1b6fb200f89c63fa54c
 ├─────── memory: 256 MiB
 ├────── service: patient-snow-zdzhdy8r
 ├─ private fqdn: httpserver-c-debug-5pvem.internal
 └─── private ip: 10.0.0.109
```

</CodeTabs>

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:

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

```text
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:

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

Then connect to the instance via SSH using:

```bash
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:

<CodeTabs syncKey="cli">

```bash title="unikraft"
unikraft instances list
```

```bash title="kraft"
kraft cloud instance list
```

</CodeTabs>

<CodeTabs syncKey="cli">

```ansi title="unikraft"
METRO  NAME                      STATE    IMAGE                        ARGS  MEMORY  VCPUS  FQDN                                    CREATED
fra    httpserver-c-debug-5pvem  running  <my-org>/httpserver-c-debug        256MiB  1      patient-snow-zdzhdy8r.fra.unikraft.app  2 minutes ago
```

```ansi title="kraft"
NAME                      FQDN                                    STATE    STATUS       IMAGE                                                     MEMORY   VCPUS  ARGS  BOOT TIME
httpserver-c-debug-5pvem  patient-snow-zdzhdy8r.fra.unikraft.app  running  since 4mins  oci://unikraft.io/<my-org>/httpserver-c-debug@sha256:...  256 MiB  1            66.56 ms
```

</CodeTabs>

When done, you can remove the instance:

<CodeTabs syncKey="cli">

```bash title="unikraft"
unikraft instances delete httpserver-c-debug-5pvem
```

```bash title="kraft"
kraft cloud instance remove httpserver-c-debug-5pvem
```

</CodeTabs>

## Learn more

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

<CodeTabs syncKey="cli">

```bash title="unikraft"
unikraft --help
```

```bash title="kraft"
kraft cloud --help
```

</CodeTabs>

Or visit the [CLI Reference](/cli/unikraft) or the [legacy CLI Reference](/cli/kraft/overview).
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