Moving to the Apollo Router from @apollo/gateway

If you have a federated supergraph that currently uses the Node.js @apollo/gateway library, this article describes how to move that supergraph to the Rust-based Apollo Router. We recommend the Apollo Router over @apollo/gateway for all supergraphs, because it provides significant performance improvements.

What's different?

Unlike @apollo/gateway, the Apollo Router is packaged as a static, standalone binary. To customize its behavior, you pass it a YAML configuration file at startup. If you start the router with the --hot-reload flag (or set the APOLLO_ROUTER_HOT_RELOAD environment variable to true), you can even modify that configuration without a restart.

You can download the Apollo Router source and use it as a library in a larger project. However, our goal is to remove the need to write custom code in your graph router (which is always necessary with @apollo/gateway). Instead, the Apollo Router exposes the most common critical features via declarative configuration.

Take inventory of your gateway configuration

The @apollo/gateway library is an extension to the Apollo Server library, and you need to consider your existing configuration of both libraries when moving to the Apollo Router. For example, you might be customizing which HTTP headers your subgraphs receive from client requests, or passing specific headers back to the client from specific subgraphs.

Because the Apollo Router uses an entirely different configuration mechanism, you should make a checklist of your gateway's custom behaviors to make sure those behaviors all remain when your migration is complete.

Start by looking for configuration and customizations in these places:

• Environment variables
• Non-Apollo telemetry and instrumentation (e.g., OpenTelemetry or Datadog)
• Constructor options passed to new ApolloGateway({ ... })
• Constructor options passed to new ApolloServer({ ... })
• Specific plugins passed to new ApolloServer({ plugins: [ ... ] })
• Custom middleware (e.g., Express, Koa, Fastify)

The sections below provide more details on what to look for in each of these categories.

Environment variables

Many Apollo tools use environment variables prefixed with APOLLO_ to set certain values, such as an API key for communicating with Apollo Studio.

Make sure to note any environment variables you set in your existing gateway's environment, especially those prefixed with APOLLO_

The Apollo Router supports the following environment variables used by @apollo/gateway:

• APOLLO_KEY
• APOLLO_GRAPH_REF

The Apollo Router renames the following environment variables used by @apollo/gateway:

• APOLLO_SCHEMA_CONFIG_DELIVERY_ENDPOINT → APOLLO_UPLINK_ENDPOINTS
  • This argument supports providing a comma-separated list of URLs.

ApolloGateway constructor options

The number of options you currently provide to your ApolloGateway constructor varies depending on whether you're using managed federation. If you are using managed federation, you might even be providing zero options to this constructor!

supergraphSdl

The supergraphSdl option is used in non-managed federation to provide a composed supergraph schema via a file or other string. Usually, that schema is composed using the Rover CLI.

You can achieve this option's effect with the Apollo Router in one of the following ways:

• Move to managed federation with your move to the Apollo Router.

• Provide the --supergraph command-line argument to the Apollo Router on startup:

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  ./router --supergraph supergraph-schema.graphql

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  The router watches this schema file and hot-reloads it whenever it changes.

serviceList / IntrospectAndCompose

If you provide one of these constructor options, your gateway performs its own supergraph schema composition on startup. The Apollo Router does not support this in-process composition.

Instead, you need to perform composition using managed federation or the Rover CLI. With either of these methods, the Apollo Router can hot-reload its supergraph schema without restarting, and you avoid the possibility of a composition failure that results in downtime.

buildService

The buildService function enables you to customize the HTTP requests that the gateway sends to your subgraphs.

Common use cases include:

• Overriding subgraph URLs at runtime
  • In the Apollo Router, you can use the override_subgraph_urls option.
• Propagating headers to subgraphs via RemoteGraphQLDataSource
  • In the Apollo Router, you can use the headers option.

logger

The logger constructor option enables you to specify a different logger for messages that are produced by the ApolloGateway. By default, it inherits from the logger used by your ApolloServer instance. This option is also useful for changing logging verbosity.

In the Apollo Router, logging is JSON-structured in production environments by default, and you can adjust the verbosity. More advanced logging can be enabled through the use of plugins.

For more information, see Logging in the Apollo Router.

ApolloServer constructor options

The ApolloServer constructor supports a large variety of options, but for the purposes of moving to the Apollo Router, we'll focus on the following:

• context
• plugins

context

This constructor option is an object that enables you to propagate information across the request lifecycle. Use cases include:

• Authentication information
• Header propagation

The Apollo Router provides similar functionality.

plugins

This constructor option is an array of built-in or custom plugins that extend Apollo Server's functionality. If you provide plugins to your ApolloServer instance, take note of each plugin's functionality and add it to your migration checklist.

Before you attempt to replicate a plugin's functionality via an Apollo Router customization, check whether any router configuration options provide that same functionality. For example, the router supports options for propagating HTTP headers to subgraphs and enabling OpenTelemetry instrumentation.

Supported customizations

The Apollo Router currently supports two types of customizations that hook into the request-handling pipeline:

• Rhai scripts
  • Rhai is a scripting language designed for use with Rust applications.
• External coprocessing

Examples for each are provided in their respective documentation, and in the Router repo.

Reporting migration issues

If you encounter a migration issue that isn't resolved by this article, please search for existing GitHub discussions and start a new discussion if you don't find what you're looking for.