Problem

When deploying to Azure App Service, users may see broken pages or errors during the deployment process. There is no built-in mechanism to show a maintenance page automatically during deployments.

Example

You need to deploy updates to your web application hosted in Azure App Service without exposing users to a partially deployed or non-functional website.

Solution

Azure App Service supports a special file named

app_offline.htm

. When this file exists in the web root directory, the App Service runtime will show this file for all incoming HTTP requests while taking the application offline.

<!-- app_offline.htm -->
<!DOCTYPE html>
<html>
<head>
    <title>Maintenance</title>
    <style>
        body {
            font-family: Arial, sans-serif;
            text-align: center;
            padding: 50px;
            line-height: 1.6;
        }
        h1 {
            color: #0078d4;
        }
    </style>
</head>
<body>
    <h1>We'll be back soon!</h1>
    <p>We're currently performing scheduled maintenance. Please check back later.</p>
</body>
</html>

Deploying app_offline.htm

Upload
```
app_offline.htm
```
to your web root directory (
```
/home/site/wwwroot
```
) before deployment
Deploy your application
Remove
```
app_offline.htm
```
when the deployment is complete

You can do this manually via Kudu (Advanced Tools) or using Azure CLI:

# Connect to your App Service
az webapp create-remote-connection --resource-group <RG> --name <AppName>

# Then use SFTP to upload the file

Automating in CI/CD Pipelines

In Azure DevOps, you can use the built-in flag in the App Service deployment task:

- task: AzureRmWebAppDeployment@4
  inputs:
    ConnectionType: 'AzureRM'
    azureSubscription: '<Your Subscription>'
    appType: 'webApp'
    WebAppName: '<AppName>'
    packageForLinux: '$(System.DefaultWorkingDirectory)/drop/*.zip'
    TakeAppOfflineFlag: true

Result

When deploying with

app_offline.htm

All users will see the maintenance page
Your application will be safely shut down during deployment
Once deployment completes and the file is removed, the app automatically restarts

For zero-downtime deployments in production environments, consider using Blue-Green/Canary/Deployment Slots instead of the

app_offline.htm

approach.

Happy Coding :)