What is Azure App Service?
Azure App Service is a Platform as a Service (PaaS) offering for hosting:
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Web applications
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REST APIs
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Mobile backends
You don’t manage servers or OS — Azure handles patching, scaling, and infrastructure. You just deploy your code.
App Service Plans
An App Service Plan defines the region, VM size, and pricing tier for your apps.
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Free / Shared: Basic tiers for testing/dev.
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Basic: Dedicated compute, manual scaling.
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Standard: Autoscaling + staging slots.
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Premium: Advanced features, better performance, VNET integration.
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Isolated (ASE): Runs in a private environment, highest security + scale.
Exam trick: If you see “staging slots” or “VNET integration”, the answer is Standard or Premium tiers, not Free/Basic.
Scaling Options
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Vertical Scaling: Change to a bigger App Service Plan (e.g., more CPU/RAM).
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Horizontal Scaling: Run multiple instances of your app (manual or autoscale).
Deployment Slots
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Let you run multiple versions of your app (e.g., staging, production).
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Deploy to staging first → test → swap into production with zero downtime.
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Great for safe deployments and rollbacks.
Confusion Buster 🚨
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App Service vs VM
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VM = Full control, manage OS + infra.
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App Service = Focus only on code, Azure handles infra.
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App Service vs Functions
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App Service = long-running web apps/APIs.
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Functions = short-lived, event-driven code.
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Simple Example
A startup hosts its website in Azure App Service using the Standard Plan.
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They set up a staging slot for new code.
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They configure autoscale to handle traffic spikes.
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Developers deploy via GitHub Actions → staging → swap to production with zero downtime.
Exam Tip
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If the requirement is “host a web app with staging and zero-downtime deployment” → App Service with Deployment Slots.
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If the requirement is “integrate app with on-prem resources via VNet” → Premium Plan.
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If the requirement is “lowest cost for simple test site” → Free/Shared Plan.
What to Expect in the Exam
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Direct Q: “Which App Service plan allows deployment slots?” → Standard or higher.
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Scenario: “Company wants zero downtime while upgrading web app.” → Deployment Slots.
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Trick Q: “App Services require you to patch the OS manually.” (False — Azure handles that).