Auto-registration of max query complexity/depth instrumentations if property is set

[marceloverdijk]

spring-graphql auto-configuration already supports picking Instrumentation beans and registering them in the GraphQlSource.
So it's just a matter of creating an instrumentation bean and it works 👍

One of the important (security) aspects to consider when developing a GraphQL server, is to make sure clients will not exhaust it by querying too many levels or fields.
E.g. when having a circular model a bad client could request many many levels deep almost causing an infinite loop.

So a good practice is:

• to have a limit on the length of the GraphQL query passed to the engine itself
• to have a limit on query depth
• to have a limit on query complexity (number of fields requested)

For the latter 2 graphql-java provides 2 instrumentation already.

I would be nice if user could enable these instrumentation by just providing an application property like:

spring.graphql.instrumentation.max-query-complexity=200
spring.graphql.instrumentation.max-query-depth=20

The starter could then contain something like below to register the beans:
(this is actually what I have now in my own application)

    @Bean
    @ConditionalOnMissingBean
    @ConditionalOnProperty(prefix = "spring.graphql.instrumentation", name = "max-query-complexity")
    public MaxQueryComplexityInstrumentation maxQueryComplexityInstrumentation(@Value("${spring.graphql.instrumentation.max-query-complexity}") int maxComplexity) {
        return new MaxQueryComplexityInstrumentation(maxComplexity);
    }

    @Bean
    @ConditionalOnMissingBean
    @ConditionalOnProperty(prefix = "spring.graphql.instrumentation", name = "max-query-depth")
    public MaxQueryDepthInstrumentation maxQueryDepthInstrumentation(@Value("${spring.graphql.instrumentation.max-query-depth}") int maxDepth) {
        return new MaxQueryDepthInstrumentation(maxDepth);
    }

(off course better to add the instrumentation properties to the actual GraphQlProperties class)

If interested I could create a PR for this?

[bclozel]

Thanks for creating this issue, this is something we'd like to explore more generally. I'd like to repurpose this issue for a broader query complexity/depth support with:

1. check whether we can add some instrumentation around query complexity/depth for metrics
2. see if there's a need for a specific mechanism in Spring Boot or Spring for GraphQL for auto-registration/auto-detection of field complexity calculator
3. optionally register the instrumentation implementations mentioned in this issue

[bclozel]

Moving this issue back to Spring for GraphQL, as this is likely to happen in the 1.1.x line and projects should provide Observation support directly with Micrometer 1.10.