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Implementing Blue-Green Deployment for an Angular Application

This challenge focuses on simulating a blue-green deployment strategy for a simple Angular application. Blue-green deployment is a release strategy that minimizes downtime and risk by running two identical production environments: "Blue" and "Green". When deploying a new version, it's deployed to the inactive environment (e.g., Green), tested, and then traffic is switched from the active environment (e.g., Blue) to the new one.

Problem Description

Your task is to create a simplified model of a blue-green deployment system within an Angular application context. This involves simulating the ability to deploy new versions of an application and switch traffic between them. The core of the challenge is to manage the deployment states and how the application "knows" which version is currently active.

What needs to be achieved:

  1. Represent Deployment States: Model how different versions of the Angular application can exist and be in various states (e.g., "Deploying", "Active", "Inactive", "Failed").
  2. Simulate Version Switching: Implement a mechanism to switch the "active" version of the application.
  3. Display Current Version: The application should clearly indicate which version is currently being served.

Key requirements:

  • Version Identification: Each deployed version needs a unique identifier (e.g., a version string like "v1.0.0", "v1.1.0").
  • Active/Inactive Status: A clear distinction between the currently serving version and any other deployed versions.
  • Simulated Deployment Process: While not a full CI/CD pipeline, you should simulate the idea of deploying a new version.
  • User Feedback: The user should be able to see the current active version.

Expected behavior:

  • The application starts with an initial "Blue" version active.
  • A mechanism (simulated by a button or service call) allows for deploying a new "Green" version.
  • Once deployed, the "Green" version can be switched to become the active version.
  • During the switch, the application should display feedback about the process.
  • Only one version can be active at any given time.

Important edge cases to consider:

  • What happens if a new version fails to deploy or test (simulated)?
  • How is the initial version handled?

Examples

Example 1: Initial State and First Deployment

Input:
- Application starts.
- No previous deployments.

Output:
- UI displays: "Current Active Version: v1.0.0 (Blue)"
- Buttons available: "Deploy New Version"

Explanation: The application initializes with a default "Blue" version. The user can initiate the deployment of a new version.

Example 2: Deploying and Switching to Green

Input:
- Application is running v1.0.0 (Blue).
- User clicks "Deploy New Version".
- A new version, v1.1.0 (Green), is simulated as deployed.
- User clicks "Switch to Green Version".

Output:
- During switch: UI displays: "Switching to v1.1.0 (Green)..."
- After switch: UI displays: "Current Active Version: v1.1.0 (Green)"
- The previous version v1.0.0 (Blue) is now marked as inactive.
- Buttons available: "Deploy New Version", "Rollback to Blue" (optional but good practice)

Explanation: A new version is deployed, and then traffic is switched to it, making it the active version. The older version becomes inactive.

Example 3: Simulating a Failed Deployment

Input:
- Application is running v1.1.0 (Green).
- User clicks "Deploy New Version".
- A new version, v1.2.0 (Blue), is simulated as failing its deployment tests.

Output:
- During deployment attempt: UI displays: "Deploying v1.2.0 (Blue)..."
- After failed deployment: UI displays: "Deployment of v1.2.0 (Blue) failed."
- Application remains on v1.1.0 (Green) as active.
- Buttons available: "Deploy New Version"

Explanation: If a deployment attempt fails, the system should not switch to the new version and should inform the user of the failure. The current active version remains unchanged.

Constraints

  • The solution should be implemented within an Angular application structure.
  • Use TypeScript for all application logic.
  • Focus on the front-end simulation of the deployment states and switching. No actual server-side deployment logic is required.
  • The UI should be clear and provide feedback on the current state and actions.
  • The number of concurrent deployed versions to manage in your simulation should be kept to a maximum of two at any given time (Blue and Green).

Notes

  • Consider using Angular services to manage the deployment state and logic.
  • You might want to simulate the "deployment" and "switching" processes with simple setTimeout functions to mimic asynchronous operations.
  • Think about how you will represent the different versions and their states. An array of objects or a dedicated service class could be useful.
  • For UI display, simple text messages or status indicators will suffice.
  • The "rollback" functionality is an excellent extension if time permits, demonstrating how to switch back to a previously active version.
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