PuiChee (PC) Chan provides a technical overview of blue-green deployment in Azure Container Apps using the Azure Developer CLI, with hands-on steps for setup, revision management, and CI/CD automation.

Blue-Green Deployment in Azure Container Apps Using Azure Developer CLI

By PuiChee (PC) Chan

Blue-green deployments allow teams to minimize downtime and reduce risk when releasing new application versions. This guide demonstrates how to execute blue-green deployments for Azure Container Apps (ACA) by leveraging the Azure Developer CLI (azd), Bicep infrastructure-as-code, and CI/CD pipelines with GitHub Actions.

Overview

Azure Developer CLI (azd) now supports Azure Container Apps with revision-based deployments.
Blue-green deployments let you maintain both ‘blue’ (current) and ‘green’ (new) revisions, directing traffic between them with minimal disruption.
The process is controlled via environment variables, Bicep parameters, and automated workflows.

Prerequisites

Azure subscription
Azure Developer CLI installed
Docker (for building images)
Python (sample app in walkthrough)

Local Deployment Workflow

Initialize the Project
- Create an empty folder and run:
```
azd init -t puichan/aca-blue-green
```
Deploy Blue Revision
- Set environment variables and deploy:
```
azd env set BLUE_COMMIT_ID fb699ef
azd env set LATEST_COMMIT_ID fb699ef
azd up
```
- Result: Only the blue revision is created if GREEN_COMMIT_ID is not set.

Create Green Revision (Keep Traffic on Blue)

Add green revision, but keep traffic routed to blue:

azd env set GREEN_COMMIT_ID c6f1515
azd env set LATEST_COMMIT_ID c6f1515
azd env set PRODUCTION_LABEL blue
azd deploy

Traffic Management
- The PRODUCTION_LABEL environment variable determines which revision receives production traffic. Changing it and redeploying swaps traffic between blue and green.
- Traffic split logic is encoded in the web.bicep file.

Viewing Endpoints

Get FQDNs for production, blue, and green deployments:

$uri = azd env get-value "SERVICE_WEB_URI"
$domain = ([System.Uri]$uri).Host.Split('.', 2)[1]
Write-Host "Production FQDN: $uri"
Write-Host "Blue label FQDN: https://web---blue.$domain"
Write-Host "Green label FQDN: https://web---green.$domain"

Switch Traffic to Green
- To direct all production traffic to the green revision:
```
azd env set PRODUCTION_LABEL green
azd deploy
```
Rollback to Blue
- Restore blue revision as production:
```
azd env set PRODUCTION_LABEL blue
azd deploy
```

CI/CD Pipeline with GitHub Actions

A sample azure-dev.yml workflow is provided to automate deployments.
The workflow uses the current commit ID as the revision label and manages blue-green alternation based on ACA tags and state, automating both new deployments and traffic switches.
ACA garbage collects old, inactive revisions beyond a configured threshold.

Key Concepts & Best Practices

Immutability: ACA revisions are immutable; deployments always create a new revision, simplifying rollback and auditing.
Bicep & IaC: Use Bicep templates for declarative infrastructure, mapping environment variables to Bicep parameters for automation.
Automated Rotation: Deployments alternate blue and green, with state managed in ACA tags and controlled through CI/CD workflows.
Manual or Automated Management: Both local CLI commands and GitHub Actions pipelines can be used to control deployments and traffic splits.

Resources

Conclusion

The blue-green deployment pattern is now straightforward for Azure Container Apps with the Azure Developer CLI’s revision-based strategy. This enables robust, production-grade rollouts with minimal downtime and easy rollbacks. The immutability of revisions and declarative Bicep workflows simplify lifecycle management, while CI/CD automation provides repeatable, reliable deployments.

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