feat: Add JSON Log Format Support to Vault CSI Provider

[khajanB]

Summary

This PR adds support for JSON-formatted logging to the vault-csi-provider, enabling better integration with log aggregation systems like Datadog, ELK, and Splunk.

Changes

Core Implementation

New CLI Flag:

• Added -log-format flag with support for json and text formats
• Default format remains text to maintain backward compatibility
• Case-insensitive validation (accepts JSON, TEXT, etc.)

Files Modified:

• main.go: Implemented setupLogger() function with format selection logic
• internal/config/config.go: Added LogFormat field to FlagsConfig

Testing

Unit Tests (main_test.go):

• TestSetupLoggerFormat: Validates format configuration (JSON, TEXT, default)
• TestSetupLoggerFormatValidation: Tests case-insensitive validation
• TestSetupLoggerIntegration: End-to-end JSON output verification
• All existing tests continue to pass

Test Configuration:

• test/bats/configs/vault-csi-provider-test.yaml: Kubernetes test manifest
• test/bats/configs/test-app-with-vault-secrets.yaml: Sample app for mount testing

Usage

Command Line

# JSON format (for log aggregation systems)
vault-csi-provider -log-format=json -log-level=info

# Text format (human-readable, default)
vault-csi-provider -log-format=text -log-level=info

Kubernetes Deployment

args:
- -endpoint=/provider/vault.sock
- -log-level=info
- -log-format=json  # Add this line

Example Output

JSON Format

{"@level":"info","@message":"Logger initialized","@module":"vault-csi-provider","@timestamp":"2025-10-07T23:14:08.986Z","format":"json","level":"info"}
{"@level":"info","@message":"Creating new gRPC server","@module":"vault-csi-provider","@timestamp":"2025-10-07T23:14:08.987Z"}
{"@level":"info","@message":"Processing unary gRPC call","grpc.method":"/v1alpha1.CSIDriverProvider/MountSecretsStoreObjectContent","@timestamp":"..."}

Manual Testing

# Build and test locally
go build -o vault-csi-provider .
./vault-csi-provider -log-format=json -log-level=debug

Benefits

1. ✅ Better Observability: JSON logs are easily parsed by log aggregation systems
2. ✅ Structured Data: All log fields are machine-readable (timestamp, level, message, context)
3. ✅ Backward Compatible: Default behaviour unchanged (text format)
4. ✅ Production Ready: Includes comprehensive unit and integration tests

Migration Guide

For existing deployments wanting to switch to JSON logging:

1. Update your Kubernetes manifests to include -log-format=json in container args
2. Update log parsing rules in your monitoring system to handle JSON format
3. No other changes required - all log levels and functionality remain the same

Related Issues

#177

PCI review checklist

• I have documented a clear reason for, and description of, the change I am making.

• If applicable, I've documented a plan to revert these changes if they require more than reverting the pull request.

• If applicable, I've documented the impact of any changes to security controls.

  Examples of changes to security controls include using new access control methods, adding or removing logging pipelines, etc.

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