tutorial.md

Metaparticle/Package for Golang Tutorial

This is an in-depth tutorial for using Metaparticle/Package for Go.

For a quick summary, please see the README.

Initial Setup

Check the tools

The docker command line tool needs to be installed and working. Try: docker ps to verify this. Go to the install page if you need to install Docker.

The mp-compiler command line tool needs to be installed and working. Try mp-compiler --help to verify this. Go to the releases page if you need to install the Metaparticle compiler.

Get the code

$ git clone https://github.com/metaparticle-io/package
$ cd tutorials/go/
# [optional, substitute your favorite editor here...]
$ code .

Initial Program

Inside of the tutorials/go directory, you will find a simple go web server.

You can build this project with go build main.go.

The initial code is a very simple "Hello World"

package main

import (
	"fmt"
	"log"
	"net/http"
	"os"
)

var port int32 = 8080

func handler(w http.ResponseWriter, r *http.Request) {
	hostname, _ := os.Hostname()
	fmt.Fprintf(w, "Hello metaparticle from %s %s!\n", r.RequestURI, hostname)
	fmt.Printf("Request received: %s\n", r.RequestURI)
}

func main() {
     log.Printf("Starting server on :%d\n", port)
     http.HandleFunc("/", handler)
     if err := http.ListenAndServe(fmt.Sprintf(":%d", port), nil); err != nil {
     	log.Fatal("Couldn't start the server: ", err)
     }
}

Step One: Containerize the Application

To build a container from our simple application we need to add a dependency to our build file, and then update the code.

Run:

$ go get github.com/metaparticle-io/package/go/metaparticle

Then update the code to read as follows:

package main

import (
	"fmt"
	"log"
	"net/http"
	"os"
	"github.com/metaparticle-io/package/go/metaparticle"
)

var port int32 = 8080

func handler(w http.ResponseWriter, r *http.Request) {
	hostname, _ := os.Hostname()
	fmt.Fprintf(w, "Hello metaparticle from %s %s!\n", r.RequestURI, hostname)
	fmt.Printf("Request received: %s\n", r.RequestURI)
}

func main() {
	metaparticle.Containerize(
		&metaparticle.Package{
			Name:       "metaparticle-web-demo",
			Repository: "your-docker-user-goes-here",
			Builder:    "docker",
			Verbose:    true,
			Publish:    true,
		},
		func() {
			log.Printf("Starting server on :%d\n", port)
			http.HandleFunc("/", handler)
			err := http.ListenAndServe(fmt.Sprintf(":%d", port), nil)
			if err != nil {
				log.Fatal("Couldn't start the server: ", err)
			}
		})
}

You will notice that we added a &metaparticle.Package struct that describes how to package the application. You will need to replace your-docker-user-goes-here with an actual Docker repository path.

You will also notice that we wrapped the main function in the metaparticle.Containerize function which kicks off the Metaparticle code.

go run main.go

This code will start your web server again. But this time, it is running inside a container. You can see this by running:

docker ps

Step Two: Exposing the ports

If you try to access the web server on http://localhost:8080 you will see that you can not actually access the server. Despite it running, the service is not exposed. To do this, you need to add a &metaparticle.Runtime struct to supply the port(s) to expose.

The code snippet to add is:

...
		&metaparticle.Runtime{
			Ports:    []int32{port},
			Executor: "docker",
		},
...

This tells the runtime the port(s) to expose. The complete code looks like:

package main

import (
	"fmt"
	"log"
	"net/http"
	"os"

	"github.com/metaparticle-io/package/go/metaparticle"
)

var port int32 = 8080

func handler(w http.ResponseWriter, r *http.Request) {
	hostname, _ := os.Hostname()
	fmt.Fprintf(w, "Hello metaparticle from %s %s!\n", r.RequestURI, hostname)
	fmt.Printf("Request received: %s\n", r.RequestURI)
}

func main() {
	metaparticle.Containerize(
		&metaparticle.Runtime{
			Ports:    []int32{port},
			Executor: "docker",
		},
		&metaparticle.Package{
			Name:       "metaparticle-web-demo",
			Repository: "your-docker-user-goes-here",
			Builder:    "docker",
			Verbose:    true,
			Publish:    true,
		},
		func() {
			log.Printf("Starting server on :%d\n", port)
			http.HandleFunc("/", handler)
			err := http.ListenAndServe(fmt.Sprintf(":%d", port), nil)
			if err != nil {
				log.Fatal("Couldn't start the server: ", err)
			}
		})
}

Now if you run this with dotnet run your webserver will be successfully exposed on port 8080.

You can verify that it works by running curl localhost:8080

Replicating and exposing on the web.

As a final step, consider the task of exposing a replicated service on the internet. To do this, we're going to expand our usage of the &metaparticle.Runtime tag. First we will add a replicas field, which will specify the number of replicas. Second we will set our execution environment to metaparticle which will launch the service into the currently configured Kubernetes environment.

Here's what the snippet looks like:

...
		&metaparticle.Runtime{
			Ports:    []int32{port},
			Executor: "metaparticle",
			Replicas: 3,
		},
...

And the complete code looks like:

package main

import (
	"fmt"
	"log"
	"net/http"
	"os"

	"github.com/metaparticle-io/package/go/metaparticle"
)

var port int32 = 8080

func handler(w http.ResponseWriter, r *http.Request) {
	hostname, _ := os.Hostname()
	fmt.Fprintf(w, "Hello metaparticle from %s %s!\n", r.RequestURI, hostname)
	fmt.Printf("Request received: %s\n", r.RequestURI)
}

func main() {
	metaparticle.Containerize(
		&metaparticle.Runtime{
			Ports:    []int32{port},
			Executor: "metaparticle",
			Replicas: 3,
		},
		&metaparticle.Package{
			Name:       "metaparticle-web-demo",
			Repository: "brendanburns",
			Builder:    "docker",
			Verbose:    true,
			Publish:    true,
		},
		func() {
			log.Printf("Starting server on :%d\n", port)
			http.HandleFunc("/", handler)
			err := http.ListenAndServe(fmt.Sprintf(":%d", port), nil)
			if err != nil {
				log.Fatal("Couldn't start the server: ", err)
			}
		})
}

You can run this using:

go run main.go

After you compile and run this, you can see that there are four replicas running behind a Kubernetes Service Load balancer:

$ kubectl get pods
...
$ kubectl get services
...

// Still looking for more? Continue on to the more advanced sharding tutorial