Azure Web App Slot Config Builder

About This Tool

Azure App Service deployment slots enable zero-downtime deployments by letting you deploy to a staging slot, validate the deployment, and then swap it into production. Slots share the same App Service Plan but can have independent configurations — app settings, connection strings, managed identity assignments, and custom domains. Configuring slots requires understanding which settings are slot-sticky (remain with the slot during swap) versus which travel with the code. The Slot Config Builder helps you design slot configurations with correct sticky settings, auto-swap rules, and pre-swap warm-up paths.

When to Use This Tool

• •Building deployment slot configurations with slot-sticky database connection strings that point staging to a staging database and production to the production database
• •Configuring auto-swap settings that automatically promote staging to production after successful health checks
• •Setting up custom warm-up paths that pre-load caches and JIT-compile code before a slot swap completes
• •Creating slot configurations for blue-green deployments with traffic routing that sends a percentage of users to the staging slot for canary testing

Frequently Asked Questions

What happens during a slot swap?

During a swap, Azure first applies the target slot's sticky settings to the source slot and restarts the workers, then waits for every instance in the source slot to complete a warm-up request. Once all instances are warm and responding, Azure swaps the virtual IPs so traffic flows to the newly warmed instances. The previous production code is now in the staging slot, making rollback a simple re-swap. The entire process maintains at least one slot handling traffic at all times.

Which settings should be slot-sticky?

Any setting that should differ between environments should be slot-sticky: database connection strings, API keys for environment-specific backends, feature flags, Application Insights instrumentation keys (if different per slot), and diagnostic settings. Settings that should travel with the code — like application behavior configuration that changes with each release — should not be sticky. A common mistake is making all settings sticky, which prevents new settings from reaching production during swaps.

Can I route a percentage of production traffic to a staging slot?

Yes, Azure App Service supports traffic routing percentages to deployment slots. You can configure production to send, for example, 10% of requests to a staging slot for canary testing. Azure uses cookie-based affinity (x-ms-routing-name) to ensure individual users consistently see the same slot during their session. This lets you validate new code with real production traffic before performing a full swap.