feat: add prometheus metric

[fatelei]

Description

fix #383

Example Metrics

Visit http://localhost:5002/metrics to see:

Plugin invocation count

plugin_invocations_total{plugin_id="openai",plugin_type="model",runtime_type="local",operation="invoke_llm",status="success"} 1234

Plugin invocation latency (histogram)

plugin_invocation_duration_seconds{plugin_id="openai",plugin_type="model",runtime_type="local",operation="invoke_llm"}

Current active invocations

plugin_invocations_active{plugin_id="openai",plugin_type="model",runtime_type="local"} 2

Plugin runtime status

plugin_runtime_status{plugin_id="openai",runtime_type="local"} 1

Active plugins

active_plugins_total{runtime_type="local"} 15

Plugin installation count

plugin_installations_total{plugin_id="openai",status="success"} 5

Plugin restart count

plugin_restarts_total{plugin_id="openai",runtime_type="local"} 1

Type of Change

• Bug fix
• New feature
• Refactor
• Performance improvement
• Other

Essential Checklist

Testing

• I have tested the changes locally and confirmed they work as expected
• I have added unit tests where necessary and they pass successfully

Bug Fix (if applicable)

• I have used GitHub syntax to close the related issue (e.g., Fixes #123 or Closes #123)

Additional Information

Please provide any additional context that would help reviewers understand the changes.

[gemini-code-assist]

Summary of Changes

Hello @fatelei, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request significantly enhances the application's observability by integrating Prometheus metrics. It provides a detailed view into the system's performance and behavior, covering HTTP request handling, the lifecycle of plugins from installation to runtime, and their invocation patterns. This will allow for better monitoring and debugging of the application's operations.

Highlights

• Prometheus Metrics Integration: Introduced comprehensive Prometheus metrics to monitor various aspects of the application, including HTTP requests, plugin invocations, and plugin lifecycle events.
• New Metrics Endpoint: A new /metrics HTTP endpoint has been added to expose the collected Prometheus metrics, making them accessible for monitoring systems.
• Plugin Observability: Detailed metrics are now collected for plugin activities such as invocation counts, invocation latency, active invocations, installation status, installation duration, runtime status, and active plugin counts.
• HTTP Request Monitoring: Implemented middleware to track total HTTP requests and their durations, categorized by method, endpoint, and status.

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[gemini-code-assist]

Code Review

This pull request introduces Prometheus metrics for monitoring various aspects of the application, including HTTP requests, plugin invocations, installations, and runtime status. This is a valuable addition for observability. The implementation is solid, but I've identified a critical issue with metric cardinality in the HTTP middleware that could negatively affect your Prometheus instance. Additionally, I've suggested several refactorings to address code duplication and improve maintainability. Overall, great work on enhancing the application's monitoring capabilities.