Grant access to the graph on a per-client basis, and manage what and how clients can access it.
Authorization in a data graph has two equally important aspects: access control, which dictates which objects and fields a user is allowed to access, and demand control, which dictates how (and how much) the user is allowed to access those resources. While access control is often talked about, attention also needs to be given to demand control, since it is critical in any production deployment of GraphQL. It is a mistake to allow users to perform any possible query regardless of cost, with no ability to manage its impact on production systems. Both access and demand control must be performed with full awareness of the semantics and performance of the data graph. It's not sufficient to limit a user to particular number of queries per minute without an analysis of the queries actually being sent, as a query could access a wide universe of services and the cost of a query can vary over multiple orders of magnitude.
Authentication in a data graph also has two aspects: the app that is requesting the operation, and the person that is using the app. While access control may center on the person using the app, proper demand control depends at least as much on per-app controls as it does on per-person controls, as it is the developer of the app, not the user of the app, that is responsible for the particular query shapes that the app uses to do its job.
Best practices for demand control include:
Capture structured logs of all graph operations and leverage them as the primary tool for understanding graph usage.
A wealth of information can be captured about each operation (read or write) that is performed on a graph: what user and app performed the operation, what fields were accessed, how the operation was actually executed, how it performed, and more. This information is highly valuable and should be systematically captured and made available for later use. Instead of a text log, it should be captured in a structured, machine readable format so that it can be leveraged for as many purposes as possible.
The record of a graph operation is called a trace. A trace should bring together all pertinent information about an operation in one place, including business information (who performed the operation, what was accessed or changed, which feature of which app built by which developer, whether it succeeded, how it performed) and purely technical information (which backend services were contacted, how each service contributed to latency, whether caches were used).
Because traces truly capture how a graph is being used, they can be used for a wide range of purposes:
Traces for all graph operations should be collected in one central place, so that there is one authoritative stream of traces. This stream can then be piped into other observability systems (perhaps after a simple transformation for existing systems that are not GraphQL-aware), or stored in one or more data warehouses for later use (aggregated and sampled as budget, use cases, and scale require).
Adopt a layered architecture with data graph functionality broken into a separate tier rather than baked into every service.
In most API technologies, clients do not talk directly to servers, except possibly in development. Instead, a layered approach is adopted in which some concerns such as load balancing, caching, service location, or API key management are split into a separate tier. This tier can then be designed, operated, and scaled separately from the backend services.
It's no different with GraphQL. Rather than baking all of the functionality needed for a complete data graph system into each and every service, most data graph functionality should be factored out into a separate tier that sits in between clients and services, leaving each service to focus on serving the actual client request. This tier, which can be composed of multiple processes, performs functions such as access and demand control, federation, trace collection, and potentially caching. Some parts of this tier will be GraphQL-specific and require deep awareness of the data graph, while other functions such as load balancing and client authentication can likely be performed by systems that are already in place.
This separate tier is valuable even in simple scenarios with only one app and only one service; otherwise, functionality that properly belongs in the middle tier will have to be implemented in the server. In complex applications, this tier may start to look like a geographically distributed system: receiving incoming queries through multiple ingress points, processing some of them on the edge of the network with the benefit of edge caches, routing subcomponents of the queries to multiple data centers in the public cloud, privately operated, or operated by partners, and finally assembling these components into a query result, all while recording a trace that memorializes the entire operation.
In some cases, this data graph tier will talk to the backend services using GraphQL. But, most frequently, the backend services are left untouched and continue to be accessed by their existing APIs, such as REST, SOAP, gRPC, Thrift, or even SQL, with the mapping from these APIs to data graph objects accomplished by servers that form one part of the data graph tier.