Monolith to Microservices 1

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This is a new series I’ve decided to write, which covers the current experiment I’m running with .NET Core 2.1, Azure DevOps, Docker and eventually Kubernetes.

I want to demonstrate how we break up a simplified example of a monolithic application containing self hosted WebAPI services into a number of microservices.

Code is hosted here:

https://github.com/r3adm3/monolithsvc and https://github.com/r3adm3/multiservice

The continuous integration pipelines are here :

https://techfrontier.visualstudio.com/dockerOrchestrationExperiment/_build?definitionId=22

Episode 1 then. Lets make a monolith.

Make sure on your chosen platform of choice you’ve got .NET SDK v5.0 installed.

Create a folder called monolithsvc and cd into it and then type:

1dotnet new mvc

This creates a boilerplate application ASP.NET Core MVC application. You can run it any time by doing:

1dotnet run

By default the application will listen on port 5000. You should see something like this:

Boilerplate .NET Core 2.1 App

I’m not going to explain too much about Model-View-Controllers or WebAPI….but what we will do is create a number of controllers which will do some simple maths which we’ll change the front page to call into.

In the controllers folder create a new file called addController.cs, here’s the contents of mine:

 1using System;
 2using System.Collections.Generic;
 3using System.Linq;
 4using System.Threading.Tasks;
 5using Microsoft.AspNetCore.Mvc;
 6using monolithsvc.Models;
 7
 8namespace monolithsvc.Controllers
 9{ 
10   [Route("api/[controller]")]
11   [ApiController]
12   public class addController : ControllerBase
13   {
14       // GET api/values
15       [HttpGet]
16       public ActionResult Get(int a, int b)
17       {
18           return (a+b);
19       }
20  }
21}

We can test this controller by launching the app with another “dotnet run” and then going to http://localhost:5000/api/add?a=2&b3

Now that’s the controller created, we need something to consume it. We’ll change the front page that has a form to collect two numbers and then use javascript to fetch the result from the controller.

Go in to Views > Home > Index.cshtml

 1<table>
 2<tbody>
 3<tr>
 4<td>First no:</td>
 5<td><input id="a" type="text" /></td>
 6</tr>
 7<tr>
 8<td>Second no:</td>
 9<td><input id="b" type="text" /></td>
10</tr>
11</tbody>
12</table>
13<button>Add</button> <button>Minus</button> <button>Multiply</button>
14<div id="result"></div>
15 
16@ViewBag.myFirstValue
17
18<script>
19    function operationFunction(op) {
20
21        var aNumber = document.getElementById("a").value
22        var bNumber = document.getElementById("b").value
23
24        if(op==='add'){var svcLink='api/add?'}
25        if(op==='minus'){var svcLink='api/minus?'}
26        if(op==='multiply'){var svcLink='api/multiply?'}
27        
28        var req = new XMLHttpRequest();
29        req.open('GET', svcLink + 'a=' + aNumber + '&b=' +bNumber , true);
30
31        req.onload = function () {
32            if (req.status >= 200 && req.status < 400) {
33                console.log ('result ' + req.responseText);
34                var result = req.responseText;
35                document.getElementById("result").innerHTML = "Result " + result;
36            } else {
37                alert('Oh dear!');
38            }
39        }
40
41        req.send();
42
43        }
44
45      
46
47</script>

…again we retest

I created controllers for taking away, adding and multiplying.

If you want to see the complete code at this stage it’s here

Next article we’ll talk about dockerising this application. http://www.techfrontier.co.uk/2019/03/02/building-up-some-microservices-breaking-up-the-monolith-2-dockerising-the-monolith/