Enterprise applications usually have different environments, such as development, staging, and production. These environments help developers to develop on the development environment, test on staging, and when everything is tested, move towards production. In Azure App Services, we can specify the deployment slot while deploying the application, and even configure the percentage of the web traffic to a particular environment to test a real-time scenario. For example, suppose we have a web application running as vms.azurewebsites.com, and we have another deployment where another upgraded version having the URL vms.staging.azurewebsites.net is running. We can test the real-time scenario by sending a percentage of the traffic to the staging web application, and once we are satisfied with the upgraded version, we can swap the production from staging. This swapping can be done without any downtime. Internally, when the swapping process starts, Azure swaps the virtual IP address assigned to the slots, and makes sure that the source slot is warmed up, so that it responds immediately when someone accesses it. Swapping can be done in both directions, that is, from staging to production and vice versa. Deployment slot is a full web application, but scaling is only possible for the deployment that has been marked as production.

Deployment slots can be configured from the Azure portal by navigating to the web application and selecting the Deployment slots option, as shown in the following screenshot:

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To check configuring the deployment slot, please refer to https://docs.microsoft.com/en-us/azure/app-service-web/web-sites-staged-publishing.