8 Years of CPU in a Day

19 Nov, 2017
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Come to Valhalla with Azure DevOps #ftw
Brian A. Randell and Ian Griffiths, DuoMyth

The idea seemed simple: bring the global community together so they could share and learn how to best use DevOps on the Microsoft stack using Visual Studio Team Services, Microsoft Azure, with Visual Studio 2017 and Xamarin tools. Do this one day a year and make the event global. This meant marshalling people, locations, and resources across the globe. But having a global meet up wasn’t enough. Xpirit wanted it to be hands-on.

On June 16, 2017, Xpirit kicked off its first Global DevOps Bootcamp in New Zealand and finished at the Western part of the continental United States. With events in Australia, India, Europe, South and North America, we were chasing the sunrise to have VMs ready to go at each location. During the event, each attendee had access to their own private dual-core Windows virtual machine running in Azure. At peak, 1,500 VMs were running using 3,000 cores of compute and over 180 terabytes of storage. Each attendee had their own private environment to work with Visual Studio, Docker, and the other tooling needed to work with the hands-on labs and get their hands dirty with DevOps in a lab environment. All made possible through hundreds of individuals putting hard work on the event, the power the Azure cloud, and Valhalla.

Come to Valhalla

Valhalla is the name of our solution built on top of Azure that makes events like the Global DevOps Bootcamp, the DockerCon 2017’s hands-on lab pavilion, and even 20-person hands-on workshops easy to run providing one or more virtual machines for each attendee. The first event hosted on Valhalla was a Microsoft ALM lab back in early 2014. Since then, Valhalla has provided a solid foundation for running traditional instructor led training classes, road-shows for Microsoft in the United States, Europe, and Middle-East as well as DockerCon 2016 and DockerCon 2017 where each lab attendee received three Linux-based VMs and/or three Windows-based VMs work with various Docker and Windows Containers related labs.

Valhalla was born out of a need to reduce the costs related to providing hands-on access to Microsoft’s ALM stack. We had been working with folks in the Microsoft US subsidiary focused on helping them find ways to make on site events at customer locations and open events at Microsoft offices better by providing customers an opportunity to try the latest versions of Visual Studio and Team Foundation Server in a hands-on experience, on demand. We had been looking at using Azure hosted virtual machines. But there were some issues. One big non-technical impediment was the original billing model. In June 2013, Microsoft moved to a per minute billing model as well as they stopped charging for compute when VMs were not running. This change pushed things over the proverbial hump. We knew we could build an affordable system on top of Azure. Moving from just ALM related content, it expanded to be a general-purpose system to provide “students” with access to a one or more VMs, all within a managed environment in the cloud.

Over the summer of 2013, we designed the system and figured out funding. In September, we started writing Valhalla originally in partnership with our friends at Endjin. In the beginning, the VMs were to run on top of the IaaS infrastructure where each virtual machine was allocated with a Cloud Service. We designed the system to support a single payee model as well as a shared payee model. We used web sites hosted in cloud services, pushing messages to queues and worker roles to process commands from the queues with table and blob storage as our persistence stores. We wanted to make the system easy to use and manage yet be flexible when it came to the types of content to support. In the beginning, we only supported Windows VMs. As Azure changed, so did we, adding support for Premium SSD storage and Linux VMs.

Valhalla Today

Naturally, creating a single virtual machine in Azure using the Azure Portal is easy. The UI guides you through the steps until you click the final button.

If you’re running regular events or even one large event you’ll obviously want to automate this—nobody wants to walk through this VM creation wizard 1,500 times. And while you might think just a little bit of PowerShell or an ARM template makes it all “simple”, it turns out it’s a bit more complicated.

From the beginning, we designed Valhalla to support flexible class deployments (type of VMs, number of VMs, number of delegates) as well as multiple subscriptions. In fact, having multiple subscriptions is a key way to scale with Azure both for performance as well as scale out. If you run events needing many hundreds of VMs you will rapidly discover that the simple resource structure you get if you create a VM through the Azure portal does not scale—you will run into Azure’s per-subscription resource limits, such as the default limit of 50 Virtual Networks. You can get this limit lifted with a support request but there’s a hard limit of 500, so you can’t use the simplistic one-VNET-per-VM model beyond that point (but equally, there can be issues if you put all your VMs on a single VNET). With careful resource design you can create thousands of VMs in a single subscription but you are then likely to run into Azure’s per-subscription API rate limiter, which can slow you down or even cause operations to fail entirely. So multiple subscription support becomes a must-have at sufficiently large scale.

At the simplest level, we want to provide a person with access (RDP or SSH) to one or more virtual machines for a period of time. In most scenarios, we provide access to the delegates via a custom e-mail message that we send out using the SendGrid service. That said, proctors at an event can hand out the delegates access information instead.

We define what VM(s) a user gets in something we call a bundle definition. A bundle defines a number of pieces of data including the recommended Azure VM size to use, whether the VM needs to be accessible through a public IP, and more.

For storage, Azure supports two types for virtual machine hard drives (VHDs): basic and premium. The difference at its core is simple: premium storage is backed by solid-state drives (SSDs). While more expensive to run long term, we’ve built optimizations into Valhalla to keep them around only as long as needed. You only pay for the time the VHDs are allocated. Premium storage can provide a more performant experience when using interactive Windows sessions in particular. We support just about any VM that you would have access to in an Azure subscription.

Valhalla Architecture.

While Azure Storage is used for VMs, we use SQL Database (Microsoft’s name for its cloud version of SQL Server) as our main persistence store for tracking classes, resources, etc. In earlier versions of Valhalla, we used Azure Table Storage. While providing good performance and cheap storage, the programming model left a bit to be desired. We found the more traditional data programming model in SQL Database more productive. We use SQL Database to store most data about the system.

Again, as we’ve evolved Valhalla, we changed how we handle security. Our original system had its own role-based security model. Our current version relies on Azure Active Directory. Currently our system is mainly accessed by ourselves and customers who need to manage classes and events. Delegates don’t need to log in to use their VMs. However, Azure AD’s flexibility means we can support other Azure accounts, MSAs, Google, Facebook, and more.

As a cloud-based solution, the main UI of the system is implemented as an Azure App Service Web App. We use slots to make it easy to deploy new versions of a site.

Web Jobs handle long-running requests. Any time Valhalla needs to do something in Azure, whether it’s scanning an Azure subscription’s storage accounts for newly-updated VHD images, or creating VMs for an event through the ARM (Azure Resource Manager) API, that work runs in a Web Job.

We use Redis Cache to enable the Web Job to provide progress notifications for its long running work to end users. We are using SignalR to enable our web servers to push notifications to browsers, and we are using SignalR’s Redis Cache backplane to make it possible for our Web Job to generate notifications that will be routed to whichever web server is managing the connection back to the relevant end user. Under the covers, this uses Redis Cache’s pub/sub mechanisms.

We use Application Insights mainly for diagnostic purposes. If something goes wrong, Application Insights is very good at providing a holistic view—you can track an operation’s progress through from some end user’s browser through to the Web App and then on through the Web Job. Application Insights provides automatic interception of any operations that use Azure Storage or SQL Azure, and the ability to discover all of the events relevant to a particular request make it easy to get a good overview of everything that happened up to the point of failure.


At this point it’s pretty clear that Azure provides us with flexible platform for our system and power on demand for our customers. However, with just two guys running the company, it helps to have a good DevOps process. Donovan Brown from Microsoft likes to say that “DevOps is the union of people, process, and product to enable continuous delivery of value for our end users.” One advantage we have is we’ve been doing software development for over fifty years between us. And our general mindset is to change our process as needed to do more with less so we can deliver value. Thus, we’ve got the people and process part down pretty good (knowing it’s a journey not a destination).

From a product perspective, we’re all-in with the cloud with Visual Studio Team Services (VSTS). Back in 2013, it wasn’t completely obvious but we started managing our source code using Git repos in VSTS. Over time, the flexible branching model has made it easy for us to work distributed across two continents and eight hours’ time difference. We use the Scrum template with Product Backlog Items, Tasks, and Bugs to plan and track our work. Our sprints are generally thirty days.

Naturally we care about quality and thus we’ve worked to build various automated quality checks into our process. It starts with unit tests that we run from within Visual Studio as well as during our automated build process. Our build process produces deployable packages, and runs a full suite of unit tests and integration tests. Our builds run using a continuous integration off master, and any feature branches which is nice when we’re working on different features.

Our release process has evolved over time and this is a critical area to keep us moving forward. With our various customers and events, updating our bits in Azure is not something we want to be doing manually. We were early adopters of the “new version” of Release Management that’s built into VSTS and it has served us well. We don’t do a typical pipe line development from dev to test to prod. What usually happens is we do lots of deployments to one of our dev environments, then to test environments followed by prod. The key is that we can have multiples of each type of environment. They’re different by purpose and customer but not by code. In addition to the deployment task, which involves pushing out any core service changes via ARM, the web sites, web jobs, as well as handling slot swaps, we use Selenium to run automated regression tests against the user interface of our web site. We have a specialized release definition for running these end-to-end tests that creates a whole new Valhalla environment (with the full set of Web Apps, SQL Server etc. deployed to a dedicated resource group) so we can test all functionality from scratch on a newly-deployed system, and this release then tears down the environment if the tests all complete successfully.

As a side note, we use Azure Key Vault to manage secrets such as SQL Server passwords and SendGrid credentials as part of DevOps. This enables us to avoid storing any secrets in source control, and also to keep them out of our build configuration. (VSTS’s ARM deployment task is able to look up the secrets itself when it needs them by accessing the Key Vault directly.)

We track a wide range of data per event such as users, VM allocations, etc. in addition to data gathered from Application Insights. We also work to have post-mortems with customers to improve the system. New feature work comes from feedback as well as from our experience at running events, large and small. The larger events, like the Global DevOps Bootcamp, help us add make the system more robust for all events.

Lessons Learned

The saying goes “there’s no place like production”. Over the years we’ve learned a number of things running on Azure. One key learning is that multiple Azure subscriptions are necessary for large scale due to hard resource limits and ARM API rate limiting. Another key learning is test, test, test. Repeatability is vital. End-to-end testing is especially valuable—our full-system tests have caught more regressions than anything else. And as always, the only constant is change. Azure is dynamic and is a fantastic platform on which to build solutions. It’s amazing to think that we can use over 180 terabytes of storage, have 1,500 VMs spun up burning eight years of CPU in a day and then give it back to the cloud. Come to the cloud, we think you’ll like it.

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