Run a Go app

In this guide we create and deploy a simple Go-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-go1.21/ directory:

git clone https://github.com/kraftcloud/examples
cd examples/http-go1.21/

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

# 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:

kraft cloud deploy -p 443:8080 .

The output shows the instance URL and other details:

[●] Deployed successfully!
 │
 ├────────── name: http-go121-9a2wv
 ├────────── uuid: 8bb34040-9434-4a28-bd1e-c24ee532e2da
 ├───────── state: running
 ├─────────── url: https://red-dew-jtk6yxk1.fra0.kraft.host
 ├───────── image: http-go121@sha256:b16d61bb7898e764d8c11ab5a0b995e8c25a25b5ff89e161fc994ebf25a75680
 ├───── boot time: 11.05 ms
 ├──────── memory: 128 MiB
 ├─────── service: red-dew-jtk6yxk1
 ├── private fqdn: http-go121-9a2wv.internal
 ├──── private ip: 172.16.3.3
 └────────── args: /server

In this case, the instance name is http-go121-9a2wv and the URL is https://red-dew-jtk6yxk1.fra0.kraft.host. They are different for each run.

Use curl to query the Unikraft Cloud instance of the Lua-based HTTP web server:

curl https://red-dew-jtk6yxk1.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-go121-9a2wv  red-dew-jtk6yxk1.fra0.kraft.host  running  1 minute ago  alex/http-go121@sha256:b16d61bb7898e764d...  128 MiB        9324us

When done, you can remove the instance:

kraft cloud instance delete http-go121-9a2wv

Customize your Application

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

• server.go: the actual Go HTTP server
• Kraftfile: the Unikraft Cloud specification
• Dockerfile: the Docker-specified application filesystem

server.go

package main

import (
  "fmt"
  "net/http"
)

func hello(w http.ResponseWriter, req *http.Request) {
  fmt.Fprintf(w, "hello, world!\n")
}

func main() {
  http.HandleFunc("/", hello)
  fmt.Println("Listening on :8080...")
  http.ListenAndServe(":8080", nil)
}

Kraftfile

spec: v0.6

runtime: base:latest

rootfs: ./Dockerfile

cmd: ["/server"]

Dockerfile

FROM golang:1.21.3-bookworm AS build

WORKDIR /src

COPY ./server.go /src/server.go

RUN set -xe; \
    go build \
      -buildmode=pie \
      -ldflags "-linkmode external -extldflags -static-pie" \
      -tags netgo \
      -o /server \
      server.go \
    ;

# This stage is optional but reduces overall image size
FROM scratch
COPY --from=build /server /server
COPY --from=build /lib/x86_64-linux-gnu/libc.so.6 /lib/x86_64-linux-gnu/
COPY --from=build /lib64/ld-linux-x86-64.so.2 /lib64/

The following options are available for customizing the application:

• If only updating the implementation in the server.go 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 new source code files are added, they have to be built using the corresponding go build command.

• If a new executable is built, update the cmd line in the Kraftfile and replace /server with the path to the new executable.

• 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:

kraft cloud --help

Or visit the CLI Reference.