Az Web App Slots
- This template provides an easy way to deploy a web app with custom deployment slots on Azure Web Apps. This Azure Resource Manager template was created by a member of the community and not by Microsoft. Each Resource Manager template is licensed to you under a license agreement by its owner, not Microsoft.
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I'm setting up a CI script for one of our Azure web apps, and I want to use deployment slots to enable per-branch deployments of the app into our development subscription. I'm able to create the deployment slot easily, and I've had some success configuring app settings via PowerShell. Start live log tracing for a web app. Az webapp restart: Restart a web app. Az webapp show: Get the details of a web app. Az webapp ssh: SSH command establishes a ssh session to the web container and developer would get a shell terminal remotely. Az webapp start: Start a web app. Az webapp stop: Stop a web app. Az webapp traffic-routing. Our system runs as a Azure Web App for containers and we use slots for switching between pre-prod and prod environment, Our issue is that sometimes, for unknown reasons.
Every App Service resource in Azure has the ability to have multiple deployment slots configure. These deployments slots are a feature than can greatly help with the implementation of streamlined testing, staging, and deployment process. Along with the ability to configure multiple hosting environments, the use of Deployment Slots enables zero downtime when deploying application changes, or even rolling back a failed deployment.
Creating Deployment Slots
Deployment slots are a feature of Azure App Service Plans. As a result, every App Service resource (Web App, Web API, Mobile App) in Microsoft Azure has the ability to create up to 4 additional deployment slots with the Standard tiers, and up to 20 deployment slots with the Premium tiers.
Each App Service (in Standard tiers) can have up to 4 additional Deployment Slots in addition to the Production slot.
Each Deployment Slot allows for a separate instance of the application to be hosted in isolation from the other deployment slots and production slot of the App Service. The VM behind each Deployment Slot is the same VM Instance that hosts the production deployment slot. This means that the App Service and 4 additional Deployment Slots will all be hosted in and share the same VM Instance and resources.
To create App Service Deployment Slots in the Azure Portal, just navigate to the App Service, select the Deployment slots section and click the Add Slot button to create a new Deployment Slot.
Additionally, in order to use the Deployment Slots feature of Azure App Service, the pricing tier must be either Standard or Premium. The Free, Shared, and Basic pricing tiers do not support deployment slots.
It’s important to keep in mind that all Deployment Slots share the same VM Instance and server resources.
Deployment Slot URL / Endpoint
Azure App Service applications get a unique URL that is made up of the App Service Name as the subdomain of the azurewebsites.net domain. In the above screen shot, the App Service Name is “testapp2063” which means the URL / endpoint for the Production slot of the App Service is located at testapp2063.azurewebsites.net.
When creating Deployment Slots each slot gets it’s own URL / Endpoint. The endpoint for each deployment slot derives from the endpoint for the Production slot by appending the name of the deployment slot with a hyphen.
With an App Service named “testapp2063” the URL / Endpoint for the following deployment slots will have the following values:
- dev => testapp2063-dev.azurewebsites.net
- test => testapp2063-test.azurewebsites.net
- stage => testapp2063-stage.azurewebsites.net
Deployment Slot Swapping
Swapping Deployment Slots is the method of copying the currently deployed application code and settings of one deployment slot and swapping it with another. Swapping allows for the deployment of application code to be done from one environment to another very quickly. It also allows for a couple new deployment techniques that didn’t exist in traditional server hosting.
To swap Deployment Slots from the Azure Portal, just navigate to the list of Deployment Slots for an App Service or navigate to the specific Deployment Slot that needs to be swapped. Then, click the Swap button and specify which Deployment Slot to swap with. See the above screenshots for reference of where the Swap button is located within the Azure Portal.
When an application is deployed using Deployment Slot swapping, there is zero downtime
When an application is deployed using Deployment Slot swapping, there is zero downtime of the application. The way this is implemented is by just rerouting the Deployment Slot Endpoint between the Deployment Slots being swapped. Both deployment slots remain running and actively responding to client requests throughout the swap.
Staged Deployment
The technique of performing a Staged Deployment allows for application code to be deployed to a non-production deployment slot (such as one named stage) to test or verify functionality is working as expected. Then once everything has been verified, the Stage deployment slot can be swapped with Production making the staged application deployment the new Production instance of the application.
Az Web App Slots App
Incremental Deployment
There are times when deploying application changes might require additional changes other than just deploying the latest code. These requirements could be running SQL scripts or some other post deployment step necessary to fully deploy the latest code. Deploying to a Stage deployment slot can allow for these Incremental steps to be performed after the code is deployed in a way that can be tested and verified before deploying to production.
Rollback Deployment
Every once in awhile a deployment fails for some reason. Maybe files end up corrupt, a major bug is found, or some other reason for failure. In these cases, it’s necessary to rollback a deployment. Using Deployment Slots, a deployment can be rolled back easily buy just swapping the Deployment Slots back.
Basically, swap Stage with Production to deploy new changes. When a major bug is found that requires a rollback, then the Production and Stage Deployment Slots can be swapped back. This allows for the old application code to be rolled back into Production in a matter of minutes. This leads to greatly decreased downtime in the event of a deployment failure.
Chris is the Founder of Build5Nines.com and a Microsoft MVP in Azure & IoT with 20 years of experience designing and building Cloud & Enterprise systems. He is also a Microsoft Certified: Azure Solutions Architect, developer, Microsoft Certified Trainer (MCT), and Cloud Advocate. He has a passion for technology and sharing what he learns with others to help enable them to learn faster and be more productive.
Timeout settings for Azure Application Gateway and App Services
Findings about various timeout settings available in Azure Application Gateway and Azure App Services
requestTimeout in Azure Application Gateway
Azure Application Gateway is a load balancer and web application firewall (WAF) in Azure, used for load distrubution, SSL termination, prevention against web based attacks (like Cross-site scripting, SQL Injection, etc) and its other features. Typically the Azure Application Gateway would be configured to route the requests to backend App Service instances to service the request.
The Application Gateway provides settings to timeout / terminate incoming requests if the backend App Service instance takes longer to process request. Following Azure CLI 2.0 based commands can be used to list the timeouts configured in the Application Gateway.
Timeouts in Azure App Service (applicationHost)
Azure App Services (including Mobile apps, Web apps, Logic apps, and others) typically run latest version of Internet Information Services (IIS 10) tweaked for Azure. Some of the basic settings for this IIS instance could be configured via Azure Portal - App Service blade. Timeout settings in Application Host level (<system.applicationHost>) can be configured via below means.
connectionTimeout in system.applicationHost/webLimits of applicationHost.config
The webLimits element in applicationHost.config specifies a default connection time out of 2 minutes. This setting could not be changed directly in the applicationHost.config file as Azure App Service does not allow to edit the file, instead supports a mechanism called XML Document Transform (XDT) which allows to append/update values to the default applicationHost.config files.
The App Service merges the default applicationHost.config and the user defined file applicationHost.xdt and uses the merged file for its configuration. Following XML content can set the connectionTimeout of webLimits to 5 minutes. Note - this XDT content need to be uploaded to the file path D:homesiteapplicationHost.xdt on the App Service instance.
connectionTimeout in system.applicationHost/sites/site of applicationHost.config
The limits element in applicationHost.config applies site wide connection timeout and defaults to 2 minutes. This can be updated using the XDT merging mechanism. Following is XDT directive for setting connectionTimeout of site limits to 6 minutes and is to be kept in the file D:homesiteapplicationHost.xdt. Note - if there is an existing applicationConfig.xdt file, the element sites and its child elements from below XDT content can be added to the <system.applicationHost> in existing applicationConfig.xdt file.
Timeouts in Azure App Service (webServer)
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Using IIS’s Delegating Configuration feature, App Service lets user to override some of the IIS settings. This can be done via custom config file, named web.config, placed in root folder of the site’s default application (typically this path will be D:homesitewwwrootweb.config). This user defined web.config supports configuring <system.webServer> and many of its child elements.
Following Azure CLI 2.0 and cURL calls to Azure Kudu VFS API commands can be used to get currently configured values in web.config
The default path to application web.config would be https://{myapp}.scm.azurewebsites.net/api/vfs/site/wwwroot/web.config. In case if you have multiple virtual path or changed default physical path, the following command can be used to get all paths that can have application level web.config file in the App Service instance.
Following command can be used to get the contents of web.config
request, activity and idle timeout for fastCgi based Python and PHP apps in Azure App Service
fastCgi directive in <system.webServer> configures the FastCGI module for executing requests using Python or PHP runtime and is used for running Python applications like Django, Flask, etc as well as PHP applications.
requestTimeout, activityTimeout and idleTimeout attributes of <fastCgi>/<application> can be used to control timeouts for the Python or PHP application.
Changes to the web.config can be uploaded back to App Service through your deployment process or through cURL commands (see invoking Azure Kudu API URL end points using cURL).
request, activity and idle timeout for Java apps running in Tomcat or Jetty container in Azure App Service
App Service IIS supports HttpPlatformHandler directive that can be used to configure Tomcat or Jetty as an external process that can inturn run Java Web Apps. The schema for the HttpPlatformHandler directive is available here. The requestTimeout can be changed via below web.config entry;
Az Webapp Slot
Other limits
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If you have setup App Services Web Server (IIS) to invoke external process, you may have to watch out
startupTimeLimit/pingResponseTimesettings in the processModel configuration