Feature Flags

Viaduct exposes certain runtime behaviours as feature flags so that service engineers can control them without redeploying. The [FlagManager][FlagManager] SPI is the integration point: implement it to bridge Viaduct flags into your organisation's flag system, or use one of the built-in implementations when you don't need dynamic control.

Default behaviour¶

If you do not call withFlagManager, Viaduct uses FlagManager.default. The default enables flags that are considered safe and stable, and disables experimental or killswitch flags. See Available flags for the per-flag defaults.

Available flags¶

All flags are defined in FlagManager.Flags.

Flag	Default	Description
`EXECUTE_ACCESS_CHECKS`	enabled	Enforces access-check directives (`@scope`, etc.) during execution. Disable only as an emergency killswitch.
`KILLSWITCH_NON_BLOCKING_ENQUEUE_FLUSH`	disabled	Reverts the data-loader coroutine dispatcher to blocking enqueue flush. Enable to recover from a regression introduced by the non-blocking implementation.
`ENABLE_SYNC_VALUE_COMPUTATION`	disabled	Allows resolvers to compute values synchronously where possible. Experimental — do not enable in production without guidance from the Viaduct team.

Wiring a FlagManager¶

Pass your implementation to ViaductBuilder.withFlagManager. The StarWars demo wires Viaduct through ViaductBuilder; adding a flag manager follows the same pattern:

production/ViaductConfiguration.kt

import io.micronaut.context.annotation.Bean
import io.micronaut.context.annotation.Factory
import viaduct.service.ViaductBuilder
import viaduct.service.api.Viaduct
import viaduct.service.api.spi.FlagManager

@Factory
class ViaductConfiguration(
    private val tenantModuleBootstrapper: MicronautTenantModuleBootstrapper,
    private val meterRegistry: MeterRegistry,
    private val flagManager: StarWarsFlagManager,
) {
    @Bean
    fun providesViaduct(): Viaduct =
        ViaductBuilder()
            .withTenantModuleBootstrapper(tenantModuleBootstrapper)
            .withMeterRegistry(meterRegistry)
            .withFlagManager(flagManager)
            .build()
}

Implementing FlagManager¶

isEnabled is called on the hot path during every query execution. Implementations must return quickly — do not perform I/O or blocking work inside isEnabled. Fetch flag state asynchronously and cache it; let isEnabled read from the cache.

class StarWarsFlagManager(
    private val flagCache: FlagCache,
) : FlagManager {
    override fun isEnabled(flag: FlagManager.Flag): Boolean =
        flagCache.get(flag.flagName) ?: FlagManager.default.isEnabled(flag)
}

Falling back to FlagManager.default for unknown flags means your service automatically picks up the recommended default for any flags added in future Viaduct releases.

Built-in implementations¶

Implementation	Behaviour
`FlagManager.default`	Framework-recommended defaults — use this as a fallback
`FlagManager.disabled`	All flags disabled — useful in tests to isolate behaviour