Agent skill

apollo-router-plugin-creator

Guide for writing Apollo Router native Rust plugins. Use this skill when: (1) users want to create a new router plugin, (2) users want to add service hooks (router_service, supergraph_service, execution_service, subgraph_service), (3) users want to modify an existing router plugin, (4) users need to understand router plugin patterns or the request lifecycle. (5) triggers on requests like "create a new plugin", "add a router plugin", "modify the X plugin", or "add subgraph_service hook".

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Install this agent skill to your Project

npx add-skill https://github.com/apollographql/skills/tree/main/skills/apollo-router-plugin-creator

Metadata

Additional technical details for this skill

author
apollographql
version
1.0.0
compatibility
Requires Apollo Router with native plugin support

SKILL.md

Apollo Router Plugin Creator

Create native Rust plugins for Apollo Router.

Request Lifecycle

┌────────┐             ┌────────────────┐                                   ┌────────────────────┐               ┌───────────────────┐       ┌─────────────────────┐
│ Client │             │ Router Service │                                   │ Supergraph Service │               │ Execution Service │       │ Subgraph Service(s) │
└────┬───┘             └────────┬───────┘                                   └──────────┬─────────┘               └─────────┬─────────┘       └──────────┬──────────┘
     │                          │                                                      │                                   │                            │
     │      Sends request       │                                                      │                                   │                            │
     │──────────────────────────▶                                                      │                                   │                            │
     │                          │                                                      │                                   │                            │
     │                          │  Converts raw HTTP request to GraphQL/JSON request   │                                   │                            │
     │                          │──────────────────────────────────────────────────────▶                                   │                            │
     │                          │                                                      │                                   │                            │
     │                          │                                                      │  Initiates query plan execution   │                            │
     │                          │                                                      │───────────────────────────────────▶                            │
     │                          │                                                      │                                   │                            │
     │                          │                                                      │                               ┌par [Initiates sub-operation]───────┐
     │                          │                                                      │                               │   │                            │   │
     │                          │                                                      │                               │   │  Initiates sub-operation   │   │
     │                          │                                                      │                               │   │────────────────────────────▶   │
     │                          │                                                      │                               │   │                            │   │
     │                          │                                                      │                               ├[Initiates sub-operation]╌╌╌╌╌╌╌╌╌╌╌┤
     │                          │                                                      │                               │   │                            │   │
     │                          │                                                      │                               │   │  Initiates sub-operation   │   │
     │                          │                                                      │                               │   │────────────────────────────▶   │
     │                          │                                                      │                               │   │                            │   │
     │                          │                                                      │                               ├[Initiates sub-operation]╌╌╌╌╌╌╌╌╌╌╌┤
     │                          │                                                      │                               │   │                            │   │
     │                          │                                                      │                               │   │  Initiates sub-operation   │   │
     │                          │                                                      │                               │   │────────────────────────────▶   │
     │                          │                                                      │                               │   │                            │   │
     │                          │                                                      │                               └────────────────────────────────────┘
     │                          │                                                      │                                   │                            │
     │                          │                                                      │  Assembles and returns response   │                            │
     │                          │                                                      ◀╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌│                            │
     │                          │                                                      │                                   │                            │
     │                          │            Returns GraphQL/JSON response             │                                   │                            │
     │                          ◀╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌│                                   │                            │
     │                          │                                                      │                                   │                            │
     │  Returns HTTP response   │                                                      │                                   │                            │
     ◀╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌│                                                      │                                   │                            │
     │                          │                                                      │                                   │                            │
┌────┴───┐             ┌────────┴───────┐                                   ┌──────────┴─────────┐               ┌─────────┴─────────┐       ┌──────────┴──────────┐
│ Client │             │ Router Service │                                   │ Supergraph Service │               │ Execution Service │       │ Subgraph Service(s) │
└────────┘             └────────────────┘                                   └────────────────────┘               └───────────────────┘       └─────────────────────┘

Service Hooks

Service Overview

Service Description
router_service Runs at the very beginning and very end of the HTTP request lifecycle.For example, JWT authentication is performed within the RouterService.Define router_service if your customization needs to interact with HTTP context and headers. It doesn't support access to the body property
supergraph_service Runs at the very beginning and very end of the GraphQL request lifecycle.Define supergraph_service if your customization needs to interact with the GraphQL request or the GraphQL response. For example, you can add a check for anonymous queries.
execution_service Handles initiating the execution of a query plan after it's been generated.Define execution_service if your customization includes logic to govern execution (for example, if you want to block a particular query based on a policy decision).
subgraph_service Handles communication between the router and your subgraphs.Define subgraph_service to configure this communication (for example, to dynamically add HTTP headers to pass to a subgraph).Whereas other services are called once per client request, this service is called once per subgraph request that's required to resolve the client's request. Each call is passed a subgraph parameter that indicates the name of the corresponding subgraph.

Signatures:

rust
fn router_service(&self, service: router::BoxService) -> router::BoxService
fn supergraph_service(&self, service: supergraph::BoxService) -> supergraph::BoxService
fn execution_service(&self, service: execution::BoxService) -> execution::BoxService
fn subgraph_service(&self, name: &str, service: subgraph::BoxService) -> subgraph::BoxService

Individual Hooks (Tower Layers)

Use ServiceBuilder to compose these hooks within any service:

Hook Purpose Sync/Async
map_request(fn) Transform request before proceeding Sync
map_response(fn) Transform response before returning Sync
checkpoint(fn) Validate/filter, can short-circuit Sync
checkpoint_async(fn) Async validation, can short-circuit Async
buffered() Enable service cloning (needed for async) -
instrument(span) Add tracing span around service -
rate_limit(num, period) Control request throughput -
timeout(duration) Set operation time limit -

Choosing a Service Hook

By data needed:

  • HTTP headers only → router_service
  • GraphQL query/variables → supergraph_service
  • Query plan → execution_service
  • Per-subgraph control → subgraph_service

By timing:

  • Before GraphQL parsing → router_service request
  • After parsing, before planning → supergraph_service request
  • After planning, before execution → execution_service request
  • Before/after each subgraph call → subgraph_service
  • Final response to client → router_service response

See references/service-hooks.md for implementation patterns.

Quick Start

Step 1: Create Plugin File

Create a new file src/plugins/my_plugin.rs with required imports:

rust
use std::ops::ControlFlow;
use apollo_router::plugin::{Plugin, PluginInit};
use apollo_router::register_plugin;
use apollo_router::services::{router, subgraph, supergraph};
use schemars::JsonSchema;
use serde::Deserialize;
use tower::{BoxError, ServiceBuilder, ServiceExt};

const PLUGIN_NAME: &str = "my_plugin";

Step 2: Define Configuration Struct

Every plugin needs a configuration struct with Deserialize and JsonSchema derives. The JsonSchema enables configuration validation in editors:

rust
#[derive(Debug, Clone, Default, Deserialize, JsonSchema)]
struct MyPluginConfig {
  /// Enable the plugin
  enabled: bool,
  // Add other configuration fields as needed
}

Step 3: Define Plugin Struct

rust
#[derive(Debug)]
struct MyPlugin {
  configuration: MyPluginConfig,
}

Step 4: Implement Plugin Trait

Implement the Plugin trait with the required Config type and new constructor:

rust
#[async_trait::async_trait]
impl Plugin for MyPlugin {
  type Config = MyPluginConfig;

  async fn new(init: PluginInit<Self::Config>) -> Result<Self, BoxError> {
    Ok(MyPlugin { configuration: init.config })
  }

  // Add service hooks based on your needs (see "Choosing a Service Hook" section)
}

Step 5: Add Service Hooks

Choose which service(s) to hook based on your requirements, see Service Overview for details.

Example service hook:

rust
fn supergraph_service(&self, service: supergraph::BoxService) -> supergraph::BoxService {
  if !self.configuration.enabled {
    return service;
  }

  ServiceBuilder::new()
    .map_request(|req| { /* transform request */ req })
    .map_response(|res| { /* transform response */ res })
    .service(service)
    .boxed()
}

Step 6: Register Plugin

At the bottom of your plugin file, register it with the router:

rust
register_plugin!("acme", "my_plugin", MyPlugin);

Step 7: Add Module to mod.rs

In src/plugins/mod.rs, add your module:

rust
pub mod my_plugin;

Step 8: Configure in YAML

Enable your plugin in the router configuration:

yaml
plugins:
  acme.my_plugin:
    enabled: true

Common Patterns

For implementation patterns and code examples, see references/service-hooks.md:

  • Enable/disable pattern
  • Request/response transformation (map_request, map_response)
  • Checkpoint (early return/short-circuit)
  • Context passing between hooks
  • Async operations (checkpoint_async, buffered)
  • Error response builders

Examples

Apollo Router Examples

Located in the Apollo Router plugins directory:

Plugin Service Hook Pattern Description
forbid_mutations.rs execution_service checkpoint Simple gate on query plan
expose_query_plan.rs execution + supergraph Context passing Multi-service coordination
cors.rs router_service HTTP layer CORS handling at HTTP level
headers/ subgraph_service Layer composition Complex header manipulation

For full code examples and testing patterns, see references/examples.md.

Prerequisites

It is advised to have the rust-best-practices skill installed for writing idiomatic Rust code when developing router plugins. If installed, follow those best practices when generating or modifying plugin code.

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