#35239 [Bug]: Microservice images (litellm-gateway / litellm-backend) never initialise the secret manager, so os.environ/<KEY> config references silently resolve to None
### Check for existing issues
- [x] I have searched the existing issues and checked that my issue is not a duplicate.
### What happened?
### What happened?
With the split/microservice images (`ghcr.io/berriai/litellm-gateway`, `ghcr.io/berriai/litellm-backend`), a config that resolves the master key and provider keys from AWS Secrets Manager does not work. The proxy starts, logs `LITELLM_MASTER_KEY is not set!`, and the Admin UI rejects the correct master key with *"Master Key not set for Proxy"*. Provider keys in `model_list` are nulled the same way, so model calls fail authentication.
The identical config, secret, and IAM role work on the monolithic image (`ghcr.io/berriai/litellm-database`) at the same versions, which isolates this to the deployment topology rather than the release.
Config used (trimmed):
```yaml model_list: - model_name: gpt-4.1 litellm_params: model: azure/gpt-4.1 api_base: "https://example.openai.azure.com/" api_version: "2024-10-21" api_key: os.environ/MY_AZURE_KEY
general_settings: master_key: os.environ/LITELLM_MASTER_KEY key_management_system: aws_secret_manager key_management_settings: aws_region_name: "us-…