Building feature branches on VSTS automatically

Currently VSTS lacks(see edit below) really handy feature, which lets you trigger a build based on a branch wildcard. For instance, I'd like to run my build definition only for refs/heads/feature/* branches. While it's super-easy when using e.g. TeamCity, with VSTS it requires us to prepare a smart workaround.

Service hooks

VSTS provides us a wide collection of different service hooks. They can be used to command builds, analyze logs or trigger any kind of an event. In fact the list of available services is already impressing and gets bigger - I strongly recommend you to take a look when you have a minute.

Besides integrating with third-party services like Slack, Bamboo or Trello, it allows us to use a simple Web Hook, which can send a specific event to a specific endpoint. Because we can send any event to any endpoint, the sky is the only limit - you can create a "lambda" using Azure Function(like me), a simple WebAPI or old but still reliable MVC application using technology stack of your choice. Whatever solution you'll create, it will work as long as it can process HTTP requests.

Kick it back!

Retrieving an event from VSTS is cool but gives information only. What we really need is to orchestrate VSTS to schedule a build using a specific build definition on a specific branch. Once again REST API provided by VSTS comes to the rescue:

/
POST https://{instance}/DefaultCollection/{project}/_apis/build/builds?api-version={version}

The important part of this request is its body:

/
{
  "definition": {
    "id": 25
  },
  "sourceBranch": "refs/heads/master",
  "parameters": "{\"system.debug\":\"true\",\"BuildConfiguration\":\"debug\",\"BuildPlatform\":\"x64\"}"
}

There're two things which are required to make it work: build definition ID and source branch. You can obtain the former from the URL when you go directly to the definition you choose, once the latter is being passed along with the whole request in data.resource.refUpdates[0].name field.

Code example

An example of a Azure Function which can handle the functionality:

public static async Task<HttpResponseMessage> Run(HttpRequestMessage req, TraceWriter log)
{
    log.Info("C# HTTP trigger function processed a request.");

    // Get request body
    dynamic data = await req.Content.ReadAsAsync<object>();

    if(data.eventType == "git.push" && data.resource.refUpdates[0].name.Value.Contains("refs/heads/feature")) {
        using(var client = new HttpClient()) {
            var branch = data.resource.refUpdates[0].name.Value;
            log.Info($"Build will be scheduled for {branch} branch.");

            client.DefaultRequestHeaders.Authorization = new AuthenticationHeaderValue("Basic", "yourToken");
            await client.PostAsync("https://{yourInstance}.visualstudio.com/DefaultCollection/{projectId}/_apis/build/builds?api-version=2.0", 
                new StringContent($"{{\"definition\": {{\"id\": {definitionId}},\"sourceBranch\": \"{branch}\"", Encoding.UTF8, "application/json"));

            log.Info($"Build scheduled successfully!.");
            return req.CreateResponse(HttpStatusCode.OK, "Build scheduled");
        }
    }

    return req.CreateResponse(HttpStatusCode.BadRequest, "Error occured");
}

Combining it all

To summarize steps needed here:

  1. Go to Service Hooks tab in VSTS and create new Web Hook pointing to your service endpoint using Code pushed as event
  2. Create a service, which will handle requests sent by VSTS and call its API to schedule a build
  3. Enjoy builds including only filtered branches

Edit:

After this was pointed I checked recently updated docs and it seems wildcard are now officially supported! You can treat this post as an inspiration for building new features around VSTS. You can find new documentation here -> https://www.visualstudio.com/en-us/docs/build/define/triggers

Replacing your application stack with Azure services

I've been thinking recently what would be the cost of Azure services, if I'd like to replace my VM with this particular cloud solutions. Please do have in mind, that in this post I'm not taking into account multiple third-party applications(like TeamCity or YouTrack), which I run on the VM along with my projects. Only technology stack matters.

What do we have?

My VM is a very basic machine:

  • Windows Server 2012
  • 1 Core AMD Opteron Processor 6386 SE 2,80 GHz
  • 50 GBs HDD storage
  • 4 GBs RAM

It's perfectly fine to run a simple SPA application, SQL server and EventStore to aggregate events from multiple devices. It's far from optimal solution but serves well since many months. Cost - about 18 EUR. 

If I had a chance to start from scratch, I'd select following stack on Azure:

  • EventHub for 10M events for 9,65 EUR
  • App Service shared infrastructure for 8,16 EUR
  • Table Storage with 50 GBs of storage and 100 transaction units for 3,26EUR

It gives total of 21,06 EUR.

Pros and cons?

While having a VM gives you great flexibility, it also complicates many things when it comes to update all software, deploy and configure it. It's also a bit more difficult to integrate all together. The biggest disadvantage of a VM is the lack of scalability - if an application will meet its higher requirements, it will cost us much more to migrate to the higher stack.

The downside of a stack built on Azure is having shared infrastructure for our web application which can(but doesn't have to be) problematic from time to time. What I like about this solution is having it all in once place and integrating it all with ease. What is more I can add Azure B2C for free and have a widely used access control solution for my application. Who knows, maybe I'll migrate to the cloud in the future?