Implement Post-Deployment Health-checks

[kornel-filep]

Add post-deployment health-checks to the AWS-CDK deployment pipelines.

The health-checks need to be integrated with Github Actions. We currently lack clarity on how to achieve this, so research into best practices or viable strategies are part of this issue. Importantly, these checks should ensure that the pipeline only concludes when the deployment is fully finished, and new webpage content is confirmed to be visible and operable.

Acceptance Criteria:

1. Research and decide on an efficient method to implement post-deployment health-checks.
2. Health-checks are implemented into both main and feature branch pipelines.
3. The pipeline process only finishes once health-checks confirm the deployment is completed fully.
4. Preferably the health-checks should also reliably work for repeat deployments - when the same branch is deployed a 2nd and 3rd time - in these cases the stack is already deployed and only the s3 bucket content changes with CloudFront invalidation (this results in a near 0 downtime).

[taughty]

Implementation Details:

Prerequisites:

• deploy pipelines implemented for main and feature branch
• deploy pipelines expose deployment URL and deployed version
• block deploy pipeline until CloudFront invalidation is completed to make sure health-check is performed against newly deployed version

Tools:

• use curl to send HTTP requests and get responses / status codes
• use pup to parse the version of the page from HTTP response

Tasks:

• add new jobs health-check to both main and feature branch pipelines
• implement a polling step to retry fetching index page from deployment URL, parsing deployed version and comparing it with the expected one up to 5 times with a 10 seconds delay between retries
• implement a conditional step that fails if the polling step fails