Adding Unary Interceptors To Pluginsdk's ServeConfig

Nov 26, 2025 by Alex Johnson 53 views

Enhancing gRPC Server Interceptors in pluginsdk: A Deep Dive into UnaryInterceptors Support for ServeConfig

In the realm of plugin development, ensuring robust communication and streamlined processes is paramount. The pluginsdk.ServeConfig structure plays a pivotal role in this, especially when dealing with gRPC servers. This article delves into a significant enhancement proposal: the addition of UnaryInterceptors support to ServeConfig. We'll explore the current limitations, the proposed solution, its practical applications, and the benefits it brings to plugin development.

Understanding the Need for Unary Interceptors

At the heart of this discussion lies the necessity for gRPC interceptors. Interceptors are powerful tools that allow developers to intercept and modify gRPC calls, offering a centralized mechanism for tasks such as logging, authentication, and tracing. Currently, the pluginsdk.ServeConfig lacks the capability to register these interceptors, which presents a significant hurdle for plugins aiming to leverage these functionalities. Unary Interceptors, in particular, are crucial for handling unary RPC calls, the most common type of gRPC interaction where a client sends a single request and receives a single response. The absence of native support for UnaryInterceptors within ServeConfig necessitates workarounds that can lead to code duplication and increased complexity. Therefore, it is important to add UnaryInterceptors support to ServeConfig in pluginsdk.

The primary motivation behind this enhancement is to enable plugins to seamlessly integrate interceptors like TracingUnaryServerInterceptor(), which is provided in pulumicost-spec/sdk/go/pluginsdk/logging.go. This interceptor is designed for automatic trace_id propagation, a critical feature for distributed tracing and debugging in microservices architectures. Without this support, plugins are forced to manually extract trace_id from gRPC metadata in each handler, a redundant and error-prone process.

Examining the Current State of ServeConfig

To fully appreciate the proposed change, let's first examine the existing structure of ServeConfig. As it stands, ServeConfig is defined as follows:

type ServeConfig struct {
    Plugin   Plugin
    Port     int
    Registry RegistryLookup
}

This structure includes fields for the plugin itself (Plugin), the port on which the gRPC server will listen (Port), and a registry lookup mechanism (RegistryLookup). However, a critical piece is missing: the ability to register gRPC interceptors. When the Serve() function is invoked, it creates the gRPC server without any interceptor options:

grpcServer := grpc.NewServer()  // No interceptors

This omission means that plugins cannot leverage the benefits of interceptors for centralized request processing, leading to the aforementioned code duplication and increased maintenance overhead. The lack of interceptor support limits the ability to implement cross-cutting concerns efficiently and consistently across plugins. The current state, therefore, highlights a clear need for an enhancement to ServeConfig to accommodate gRPC interceptors.

The Proposed Solution: Adding UnaryInterceptors

The proposed solution addresses this limitation by introducing a new field to the ServeConfig structure: UnaryInterceptors. This field will be a slice of grpc.UnaryServerInterceptor, allowing plugins to register multiple interceptors that will be executed for each unary RPC call. The modified ServeConfig structure will look like this:

type ServeConfig struct {
    Plugin           Plugin
    Port             int
    Registry         RegistryLookup
    UnaryInterceptors []grpc.UnaryServerInterceptor  // NEW
}

With the addition of UnaryInterceptors, the Serve() function needs to be updated to utilize these interceptors when creating the gRPC server. This involves creating gRPC server options that include the chained interceptors. The updated Serve() function will incorporate the following logic:

opts := []grpc.ServerOption{}
if len(config.UnaryInterceptors) > 0 {
    opts = append(opts, grpc.ChainUnaryInterceptor(config.UnaryInterceptors...))
}
grpcServer := grpc.NewServer(opts...)

In this snippet, if the UnaryInterceptors slice is not empty, the grpc.ChainUnaryInterceptor function is used to chain the interceptors together. This ensures that each interceptor in the slice is executed in the order it appears. The resulting server options are then passed to grpc.NewServer() during server creation. This approach provides a flexible and extensible way for plugins to incorporate interceptors into their gRPC servers. The proposed solution not only addresses the immediate need for trace_id propagation but also opens the door for other interceptor-based functionalities in the future.

Use Case: Trace Propagation with TracingUnaryServerInterceptor

To illustrate the practical application of this enhancement, consider the use case of the pulumicost-plugin-aws-public plugin (and future plugins). This plugin aims to use the TracingUnaryServerInterceptor() to automatically propagate trace IDs across gRPC calls. With the proposed change, the plugin can configure its ServeConfig as follows:

config := pluginsdk.ServeConfig{
    Plugin: awsPlugin,
    Port:   0,
    UnaryInterceptors: []grpc.UnaryServerInterceptor{
        pluginsdk.TracingUnaryServerInterceptor(),
    },
}

By including TracingUnaryServerInterceptor() in the UnaryInterceptors slice, the plugin can ensure that trace IDs are automatically propagated without requiring manual extraction and insertion in each handler. This significantly simplifies the implementation of distributed tracing and improves the overall observability of the system. This use case highlights the immediate benefits of the proposed change in enabling better tracing and debugging capabilities. Furthermore, this approach can be extended to other interceptors for authentication, logging, and other cross-cutting concerns.

Addressing the Current Workaround

Currently, without native support for UnaryInterceptors, plugins must resort to manual workarounds to achieve similar functionality. This typically involves extracting the trace_id from gRPC metadata in each handler function. This workaround not only duplicates logic but also increases the risk of errors and inconsistencies. The manual extraction of trace_id from gRPC metadata in each handler is a tedious and error-prone process. The proposed enhancement eliminates this need, streamlining the development process and reducing the maintenance burden. By providing a centralized mechanism for interceptor registration, the new UnaryInterceptors field promotes cleaner, more maintainable code.

Benefits of the Proposed Change

The addition of UnaryInterceptors support to ServeConfig brings several key benefits to plugin development:

Simplified Trace Propagation: Plugins can easily integrate tracing interceptors like TracingUnaryServerInterceptor() without manual intervention.
Reduced Code Duplication: Centralized interceptor management eliminates the need to duplicate logic across multiple handlers.
Improved Observability: Automatic trace_id propagation enhances the ability to trace requests across microservices.
Enhanced Maintainability: Cleaner code and reduced complexity lead to easier maintenance and debugging.
Extensibility: The UnaryInterceptors slice allows for the registration of multiple interceptors, enabling a wide range of functionalities.
Consistency: Interceptors ensure consistent handling of requests across all gRPC calls.

The benefits of adding UnaryInterceptors support to ServeConfig are manifold, ranging from simplified trace propagation to improved code maintainability. This enhancement not only addresses the immediate needs of plugins like pulumicost-plugin-aws-public but also lays the foundation for future improvements and features.

Related Efforts and Context

It's important to note the context of this proposal within the broader ecosystem. The pulumicost-spec repository provides the TracingUnaryServerInterceptor() in sdk/go/pluginsdk/logging.go, which is a key component in this enhancement. Additionally, the pulumicost-plugin-aws-public plugin's feature 005-zerolog-logging explicitly requires this functionality for trace propagation. This proposal is closely tied to the ongoing efforts to improve logging and tracing within the pulumicost ecosystem. The related efforts underscore the importance of this enhancement and its alignment with broader goals.

Conclusion: Embracing Interceptors for Robust Plugin Development

The proposal to add UnaryInterceptors support to pluginsdk.ServeConfig represents a significant step forward in enhancing the capabilities of gRPC-based plugins. By providing a native mechanism for registering interceptors, this change simplifies development, reduces code duplication, and improves the overall robustness and observability of plugin systems. The use case of trace_id propagation with TracingUnaryServerInterceptor() highlights the immediate benefits of this enhancement, while the broader implications extend to other interceptor-based functionalities such as authentication and logging.

In conclusion, the addition of UnaryInterceptors to ServeConfig is a valuable improvement that aligns with the best practices of gRPC development and lays the groundwork for future enhancements in plugin architectures. By embracing interceptors, developers can build more robust, maintainable, and observable systems. For more information on gRPC interceptors and their uses, you can visit the official gRPC documentation. This external resource provides a comprehensive overview of gRPC concepts and best practices.