backend-plugin-architecture

Backend Plugin Architecture

Purpose

Design extensible backend systems where third-party code (plugins) can be loaded dynamically at runtime through well-defined extension points and service provider interfaces (SPI). A plugin architecture enables the host application to be extended without modifying its core code.

Agent Protocol

Trigger

Exact user phrases: "plugin system", "plugin architecture", "extension point", "SPI", "service provider interface", "hot-plug", "modular design", "plugin loader", "extensible", "plugin API", "custom extension", "plug-in", "dynamic loading".

Input Context

• What the host application does and where extensibility is needed.
• Language/runtime (supports dynamic loading?).
• Security requirements for plugin isolation.

Output Artifact

Plugin system design or implementation code. No file unless requested.

Response Format

Extension Point: {name}
SPI: {interface/contract}
Loading: {dynamic|compile-time|classpath}
Isolation: {classloader|process|container}

Completion Criteria

• Extension points defined and documented.
• SPI interface created for each extension point.
• Plugin loader implemented.
• Plugin lifecycle (load, init, start, stop, destroy) managed.
• Isolation and security boundaries established.

Max Response Length

3 lines per extension point. 20 lines for full system.

Architecture Decision Tree

Should I Build a Plugin System?

Do you need to support third-party extensions?
  ├── Yes → Plugin architecture
  └── No → Can the functionality be handled by configuration?
            ├── Yes → Use configuration, not plugins
            └── No → Is the extension point stable (won't change monthly)?
                      ├── Yes → Plugin architecture is appropriate
                      └── No → Plugin API will need constant breaking changes — reconsider

Plugin Loading Strategy

Can plugins be loaded at runtime without restart?
  ├── Yes → Dynamic loading (hot-plug)
  │   ├── Language supports dynamic loading (JS, Python, Java, .NET, Go plugins)
  │   ├── Plugin discovery via file system scanning or registry
  │   └── Risk: Version conflicts, dependency hell
  └── No → Compile-time loading
      ├── Simpler, safer, no runtime isolation concerns
      ├── Requires recompile/redeploy for new plugins
      └── Use when: Plugin churn is low, safety is critical