Runtime Session & Permission Changes for Container deployments

[cjackson202]

This README explains the recent changes made to app.py, config.py, and the Dockerfile to fix Docker container permission issues and runtime session initialization failures. The goal was to make the application run reliably both with code and container Azure App Service Deployments, without breaking current session functionality.

Why The Change Was Needed

When the container was deployed to Azure App Service, it crashed with:

PermissionError: [Errno 13] Permission denied: '/app/flask_session'

The app ran as a non-root user (nonroot), and Flask-Session (filesystem backend) tried to create /app/flask_session, which wasn't writable. This required fixing the Docker container's permission structure to properly handle session storage. There were also three duplicated blocks of session initialization logic in app.py that caused runtime issues when the container was deployed to App Service.

Summary of Changes

File	What Changed	Why
config.py	Added SESSION_FILE_DIR (defaults to /app/flask_session).	Ensures filesystem session storage uses a properly permissioned directory inside the container; tracks release.
app.py	Created a single configure_sessions(settings) helper. Removed three duplicated Redis/filesystem setup blocks. Ensured session directory is created early if using filesystem sessions.	Eliminates duplication, improves reliability, keeps logic in one place, supports Redis or filesystem seamlessly.
Dockerfile	Builder stage runs as root to create venv, install deps, and create/permission /app/flask_session. Final stage copies the pre-permissioned directory.	Ensures privileged steps (install/build/permission) succeed in builder, while final container follows least-privilege with proper session directory permissions.

How Session Selection Now Works

1. Admin enables Redis in settings:
   • If redis_url present → Redis backend configured (key or managed identity).
   • If enabled but URL missing → falls back to filesystem with a log message.
2. Redis not enabled → filesystem backend using SESSION_FILE_DIR (default /app/flask_session).
3. Any unexpected Redis error → graceful fallback to filesystem (no startup crash).

Container Deployment with Azure CLI

To build and deploy the container image to Azure Container Registry:

1. Navigate to the project directory:

   cd simplechat/

2. Set environment variables:

   ACR_NAME="<your-azure-container-registry-name>"
   IMAGE_NAME="simplechat"
   IMAGE_TAG="<version-tag>"  # Example: v0229062 (remove dots from version)

3. Build and push the image:

   az acr build --registry $ACR_NAME --image $IMAGE_NAME:$IMAGE_TAG -f application/single_app/Dockerfile .

Example with actual values:

ACR_NAME="mycompanyregistry"
IMAGE_NAME="simplechat"
IMAGE_TAG="v0229062"
az acr build --registry mycompanyregistry --image simplechat:v0229062 -f application/single_app/Dockerfile .

Environment Overrides (Optional)

You can override the session directory:

SESSION_FILE_DIR=/home/site/wwwroot/flask_session

(Useful only if persistent storage is enabled and you intentionally want on-disk sessions without Redis.)

Benefits

• No more permission errors during container deployment and startup.
• Clear, single place to update session handling.
• Works in both development and Azure environments.
• Easy future extension (e.g., adding diagnostics or health checks for Redis).

[aaronba]

@cjackson202 Can you make sure that ManagedIdentity code path works for AzureGovernment deployments and supports a custom Redis endpoint when getting the token (example hardcoded suffix below)

token = credential.get_token(f"https://{redis_hostname}.cacheinfra.windows.net:10225/appid")

[cjackson202]

@aaronba completed.