Azure Deployment Slots Cost

In times of rapid change, developers and IT decision-makers must quickly adjust to a drastically evolving landscape. Successful organizations use managed cloud services to reduce operating costs by increasing developer efficiency, and seize new business opportunities by accelerating delivery of innovation.

Try this tutorial to get started with App Service, GitHub Actions, and API Management.

Host applications with App Service

App Service is a proven managed service for hosting your web apps and mobile backends with deployment APIs, networking integration, and built-in monitoring.

Before I tell you even more about what make Azure deployment slots awesome, let me state the facts about deployment slots: Each deployment slot is like a full-fledged App Service instance. The original App Service deployment slot is also called the production slot. Azure Deployment Slot is a very useful feature of the Azure App Service. With this feature, it is possible to create one or more slots that can host different versions of your app. You can then swap these deployment slots without causing any downtime for your users. Deployment slots are in fact resources of the App Service itself and can be deployed as such. This means you can specify them within the resources array of your web application / App Service. ARM code for deployment slot looks like below: ARM Code for Azure Web App Slot. Here, slot name is defined inside a property named stagingSlotName.

Use your preferred technology stack to increase the speed-to-market. Build your applications with .NET, .NET Core, Java, Node.js, Python or PHP. Deploy them as code or Docker containers and integrate with API management in Visual Studio Code or the Azure Portal.

Simplify operations with GitHub Actions. Use GitHub Actions to automate the testing and deployment of your applications onto App Service’s global infrastructure. The Azure Portal makes it easy to get started with a guided developer experience. Then use deployment slots to coordinate your QA, staging, and production deployments.

Isolate and secure applications with enterprise-grade global datacenter network. Once your applications are deployed, isolate and secure them in a Virtual Network or in an App Service Environment. Get more secure, high-speed connections to resources on premises or in the cloud and maintain fine-grained control over network traffic.

Manage, protect, and publish APIs with API Management

API Management lets you manage and protect APIs throughout their lifecycle and publish them to consumers.

Increase the speed to market with one-click API import. Design the API from scratch or generate it automatically from an API definition file (OpenAPI, WSDL, WADL) or an Azure service (App Service, Functions, Logic Apps).

Simplify management of APIs. API Management abstracts the APIs from their implementation, allowing you to transform and iterate on your backend services without impacting API consumers. As the backends evolve and API traffic increases, create new API revisions and versions and monitor the usage with Azure Application Insights, Azure Monitor, or custom solutions.

Protect and secure your APIs from abusive users with policies. Apply the rate-limit-by-key policy to throttle API calls based on any key – for example, IP address or user credentials. Set long-term quotas with the quota-by-key policy to limit the allowed number of calls or data transfer. Secure your APIs with built-in API subscription keys mechanism, client certificates, or JWT tokens. The most convenient way to author policies is to use the Azure portal or the official Visual Studio Code extension with the autocomplete feature. Examples of more advanced policies are located in this GitHub repository.

Seize new business opportunities by publishing your APIs in the developer portal. Azure API Management comes with a built-in developer portal. It is an automatically generated, fully customizable website where visitors can discover your APIs, learn how to use them, try them out interactively, and sign up to acquire access. By publishing your APIs, you can scale your operations and build an ecosystem around your services. You may also monetize them to create new revenue streams.

Try the sample

To get started with App Service and API Management, clone this sample application and follow the instructions. By the end of the tutorial, you will have set up continuous delivery with GitHub Actions and exposed your backend API with API Management.

Azure App Services is extremely useful for developers. It offers Web Apps, API Apps, Mobile Apps and Function Apps (that run Azure Functions). All of these apps are incredibly powerful and can literally get you up and running in minutes. They provide a host of amazing features that you can leverage, like (auto)scaling, easy authentication, offline sync (for Mobile Apps), hybrid connections and many, many more. One feature that all of these apps share, is probably the most underrated one that many people don’t know about: deployment slots.

What Are Deployment Slots?

Deployment slots are incredible! They are the reason for many people to start using Azure App Services, like Web Apps. Let me explain why:
Suppose that you have a Web App. You run your website in it and it has an URL like production.website.com. In Azure App Services, you can very easily add a deployment slot. This is actually a full-fledged App Service, in this case a Web App, that sits next to you original Web App. The deployment slot has a different URL, maybe something like staging.website.com. Users use your website that is in the original Web App, because that is your production environment. You can deploy a new version of the website in the deployment slot, just so that you can test it before it goes live.
You could also do that in another Web App. But here is the magic of deployment slots: You can now Swap the deployment slot with production. When you do this, users will notice almost nothing and experience no downtime. The swap functionality of the deployment slot takes care of this magic. Isn’t that awesome?

Deployment Slot Facts

Before I tell you even more things that make deployment slots awesome, let me state out the facts about deployment slots:

• A deployment slot is a full-fledged App Service that lives within the same App Service Plan as your original App Service
  • This means that deployment slots use some of the resources in the App Service Plan, which could influence the performance of your main App Service
• The original App Service is also called the production slot
• Deployment slots can copy the configuration (AppSettings and Connectionstrings) of the original App Service or other deployment slots
• Your App Service needs to (at least) be in the Standard Pricing tier
• You can create 4 deployment slots next to your original App Service in the Standard Pricing tier
• And you can create 19 deployment slots next to your original App Service in the Premium Pricing tier
• When you scale a deployment slot (up or out), you also scale all the other slots of the App Service. This is because all slots share the same App Service Plan
• If you have installed any site extensions, you need to do that again in a deployment slot as it is a new App Service instance
• Deployment slots have a different URL then the original App Service. This URL is based on the name you give the deployment slot, for instance “staging” can become http://website-staging.azurewebsites.net

Alright, let’s take a look at how to setup deployment slots and what the major benefits are in more detail.

Setting up Deployment Slots

Creating a deployment slot is very easy and, as always, there are many ways to do it. You can use the Azure Portal, Azure CLI, Azure PowerShell and the Azure Management API. I’ll show you how to do it using the Azure Portal.
In the Azure Portal, navigate to your App Service - let’s say it’s a Web App - and click the deployment slots menu item:
Now you see the Add Slot button, which opens the Add Slot dialog, to the right of the screen. Here, you need to enter a name, and choose if you want to copy the configuration from another slot, or not at all. Click OK and voila, you have a deployment slot!

Choosing to copy the configuration is important, because your app probably does things like connect to a database or cache and has specific connectionstrings in these settings.

Visit my Pluralsight course for a full video tutorial about setting up and using deployment slots.

Deploying your app to deployment slots

When you have created a deployment slot, it is empty, just like when you create a new App Service. You need to deploy a version of your app to the deployment slot before you can use it.
You can use the same tools and techniques that you use to deploy your app to the App Service: through Visual Studio, using something like VSTS (Visual Studio Team Services) or Octopus Deploy, using Web Deploy or any number of other technologies. Selecting a deployment slot to deploy to from Visual Studio looks like this:

Swap and Rollback

One of the major benefits of deployment slots is that you can swap them. What does that mean?

Swapping

Suppose that I have a website deployed in a Web App. This Web App has the custom URL https://www.azure-overview.com/. I have created a new version of the website and want to test it before publishing it. So I create a deployment slot called staging, which has the URL http://azureoverview-staging.azurewebsites.net. I’ve made sure that the slot has the same configuration values so that I use the same database and cache as production does. I’ve deployed the new website in the deployment slot and I’m happy with my changes and want to deploy to production. I can do this by performing a swap:
I can do this from the Azure Portal, Azure CLI, Azure PowerShell and the Azure Management API. In the Azure Portal, I can choose what the source and destination slots are and click OK. This will swap the slots and will deploy my changes to production. Here’s the thing: Users will experience no downtime!

And that’s because a swap does the following:

• The source slot will be warmed-up. Azure does this by firing a couple requests into the root of the slot. You can also configure custom warm-up rules
• Swaps the Virtual IP addresses of the source and destination slots, thereby swapping the URLs of the slots
• It also applies (or keeps, depending on how you see it) certain settings that are specific to the target slot:
  • Publishing endpoints
  • Custom Domain Names
  • SSL certificates and bindings
  • Scale settings
  • WebJobs schedulers

This results in a seamless transition to production. Users experience virtually no downtime. I say virtually because users that are in the midst of doing something that depends on state that is in-memory of the Web App, will lose this state. But you shouldn’t keep state locally in an App Service anyways in Azure as you should assume that everything in Azure is volatile.

Rollback

After a swap, the “old” website will be in the staging slot and the “new” website in the production slot.
If you aren’t happy with the version in production, you can easily rollback your deployment. Simply swap back to reverse the effect!

Swapping options

You can swap manually, but you have more options:

Auto Swap

Azure Deployment Slots Cost Comparison

You can choose to swap automatically to a slot when there is a new version of your app in a deployment slot – this is called Auto Swap. Simply enable it in the Application Settings of the deployment slot:

Swap with preview

You can choose to swap with preview when you perform a swap from the Azure Portal. This does the following:

• It performs the swap in stages
• It applies the configuration elements of the destination slot to the source slot, so that you can test if everything works as expected, before the actual swap happens
• (if you complete the swap), it does the same as in a manual swap, warm-up the slot and perform the swap
  

Swap and VSTS

If you use something like VSTS (Visual Studio Team Services), you can also leverage deployment slots and the swap feature. You can deploy a new version of your app to a deployment slot and then swap it using steps in a release definition. The illustration below shows this for a release definition in VSTS:

Testing in Production

Besides swapping, deployment slots offer another killer feature: testing in production. Just like the name suggests, using this, you can actually test in production. This means that you can route a specific percentage of user traffic to one or more of your deployment slots:
With testing in production, you can have some users use the new version of your application. This way, you can see if and how they use new features. In order to find this out, you need to make sure that you monitor everything, with something like Stackify Retrace.

Azure Deployment Slots Cost

Setup

Testing in production is easy to setup. In the Azure Portal, choose the testing in production menu option in your App Service.
Here, you can choose the deployment slots that you want to route traffic to (or add new ones) and assign a percentage of traffic to them. That’s it! Now users will be routed to your deployment slots – super powerful!

Conclusion

Deployment slots are awesome and I hope that you give them a chance. You can use them for all sorts of things, but there are also things to keep in mind. Here is the quick overview:

Pros:

Azure Deployment Slots Cost Per

• Using the **swap **feature gives you zero-downtime deployments
• You can test the new version of your app using the testing in production feature
• Deployment slots are great to verify a new version of an app before it goes live

Cons:

• A deployment slot is a full-fledged App Service that lives within the same App Service Plan as your original App Service, which might impact the performance of your original App Service
• A deployment slot is a new App Service. This means that you have to reinstall any site extensions that you have installed in you App Service
• Your App Service needs to (at least) be in the Standard Pricing tier
• You can’t scale a deployment slot, separate from other deployment slots in the App Service. This makes a deployment slot not suitable for performance testing – you should use a separate App Service for that

Azure Deployment Slots Cost Calculator

Start using deployment slots and use them wisely! Let me know what you think in the comments.