rkt/Documentation/getting-started-guide.md

Getting Started with rkt

The following guide will show you how to build and run a self-contained Go app using rkt, the reference implementation of the App Container Specification.

Create a hello go application

package main

import (
	"log"
	"net/http"
)

func main() {
	http.HandleFunc("/", func(w http.ResponseWriter, r *http.Request) {
		log.Printf("request from %v\n", r.RemoteAddr)
		w.Write([]byte("hello\n"))
	})
	log.Fatal(http.ListenAndServe(":5000", nil))
}

Build a statically linked Go binary

Next we need to build our application. We are going to statically link our app so we can ship an App Container Image with no external dependencies.

With Go 1.3:

$ CGO_ENABLED=0 GOOS=linux go build -o hello -a -tags netgo -ldflags '-w' .

or, on Go 1.4:

$ CGO_ENABLED=0 GOOS=linux go build -o hello -a -installsuffix cgo .

Before proceeding, verify that the produced binary is statically linked:

$ file hello
hello: ELF 64-bit LSB executable, x86-64, version 1 (SYSV), statically linked, not stripped
$ ldd hello
	not a dynamic executable

Create the image manifest

Edit: manifest.json

{
    "acKind": "ImageManifest",
    "acVersion": "0.2.0",
    "name": "coreos.com/hello",
    "labels": [
        {
            "name": "version",
            "value": "1.0.0"
        },
        {
            "name": "arch",
            "value": "amd64"
        },
        {
            "name": "os",
            "value": "linux"
        }
    ],
    "app": {
        "user": "root",
        "group": "root",
        "exec": [
            "/bin/hello"
        ],
        "ports": [
            {
                "name": "www",
                "protocol": "tcp",
                "port": 5000
            }
        ]
    },
    "annotations": [
        {
            "name": "authors",
            "value": "Kelsey Hightower <kelsey.hightower@gmail.com>"
        }
    ]
}

Validate the image manifest

To validate the manifest, we can use actool, which is currently provided in releases in the App Container repository.

$ actool -debug validate manifest.json
manifest.json: valid ImageManifest

Create the layout and the rootfs

$ mkdir hello-layout/
$ mkdir hello-layout/rootfs
$ mkdir hello-layout/rootfs/bin

Copy the image manifest and hello binary into the layout:

$ cp manifest.json hello-layout/manifest
$ cp hello hello-layout/rootfs/bin/

Build the application image

$ actool build hello-layout/ hello.aci

Validate the application image

$ actool -debug validate hello.aci
hello.aci: valid app container image

Run

Launch a local application image

$ rkt run hello.aci

At this point our hello app is running on port 5000 and ready to handle HTTP requests.

Testing with curl

Open a new terminal and run the following command:

$ curl 127.0.0.1:5000
hello