Add agentless Feature Flagging configuration source

[leoromanovsky]

Motivation

Java Feature Flagging needs a tracer-side configuration-source split so SDKs can fetch UFC from an agentless Datadog backend while preserving the existing Agent Remote Configuration path.

Changes

• Adds DD_FEATURE_FLAGS_CONFIGURATION_SOURCE with agentless, remote_config, and reserved offline; default is agentless.
• Adds agentless polling controls: DD_FEATURE_FLAGS_CONFIGURATION_SOURCE_AGENTLESS_POLL_INTERVAL_SECONDS and DD_FEATURE_FLAGS_CONFIGURATION_SOURCE_AGENTLESS_REQUEST_TIMEOUT_SECONDS.
• Adds AgentlessConfigurationSource, an HTTP UFC poller for the Datadog server-distribution endpoint.
• Keeps remote_config on the existing RemoteConfigServiceImpl / Agent RC path.
• Handles DD-API-KEY, ETag/304, timeout/429/5xx retry, malformed UFC rejection, last-known-good preservation, and no overlapping polls.
• Removes the proposed DD_FEATURE_FLAGS_ENABLED, agentless base URL env, and extra-header env from this PR.

Decisions

No new provider kill switch. This keeps the existing provider bootstrap behavior through DD_EXPERIMENTAL_FLAGGING_PROVIDER_ENABLED; changing enablement is out of scope for this PR.

No public agentless base URL/header envs. The default agentless endpoint is derived from Datadog site/env as https://api.<site>/api/v2/feature-flagging/config/server-distribution?dd_env=<env>. Custom customer endpoints, dogfood proxies, and system-test proxies should be wired through an explicit custom source/client API, not process-wide env vars.

No offline factory yet. offline remains a reserved configuration-source value. This PR does not expose a startup-bytes API or offline factory because that API still needs design work.

Source selection stays SDK-local. DD_FEATURE_FLAGS_CONFIGURATION_SOURCE decides which local source implementation starts. It is not sent to the backend.

Class Shape

classDiagram
    direction LR
    class FeatureFlaggingSystem {
      +start()
      +stop()
      -createConfigurationSourceService()
    }
    class ConfigurationSourceService {
      <<interface>>
      +init()
      +close()
    }
    class RemoteConfigServiceImpl {
      +init()
      +close()
      +accept()
    }
    class AgentlessConfigurationSource {
      +init()
      +close()
      -pollOnce()
      -fetchAndApply()
    }
    class FeatureFlaggingGateway {
      +dispatch()
    }

    FeatureFlaggingSystem --> ConfigurationSourceService : selects one source
    ConfigurationSourceService <|.. RemoteConfigServiceImpl
    ConfigurationSourceService <|.. AgentlessConfigurationSource
    RemoteConfigServiceImpl --> FeatureFlaggingGateway : Agent RC UFC
    AgentlessConfigurationSource --> FeatureFlaggingGateway : HTTP UFC

Loading

Customer Usage Example

Default Datadog-hosted agentless delivery:

export DD_API_KEY=<datadog-api-key>
export DD_SITE=datadoghq.com
export DD_ENV=prod

# Optional because agentless is the default configuration source.
export DD_FEATURE_FLAGS_CONFIGURATION_SOURCE=agentless
export DD_FEATURE_FLAGS_CONFIGURATION_SOURCE_AGENTLESS_POLL_INTERVAL_SECONDS=30
export DD_FEATURE_FLAGS_CONFIGURATION_SOURCE_AGENTLESS_REQUEST_TIMEOUT_SECONDS=2

java -javaagent:/path/to/dd-java-agent.jar -jar app.jar

Explicit Agent Remote Configuration delivery still uses the existing Agent path:

export DD_FEATURE_FLAGS_CONFIGURATION_SOURCE=remote_config
export DD_REMOTE_CONFIGURATION_ENABLED=true

java -javaagent:/path/to/dd-java-agent.jar -jar app.jar

Verification

./gradlew :products:feature-flagging:feature-flagging-agent:test :products:feature-flagging:feature-flagging-lib:test --tests com.datadog.featureflag.FeatureFlaggingSystemTest --tests com.datadog.featureflag.AgentlessConfigurationSourceTest
result: BUILD SUCCESSFUL in 7s

./gradlew :products:feature-flagging:feature-flagging-agent:spotlessCheck :products:feature-flagging:feature-flagging-lib:spotlessCheck :dd-trace-api:spotlessCheck :internal-api:spotlessCheck
result: BUILD SUCCESSFUL in 5s

git diff --check
result: clean

rg "AgentlessUfcSource|UfcHttpConfigService|DD_FEATURE_FLAGS_ENABLED|DD_FEATURE_FLAGS_CONFIGURATION_SOURCE_AGENTLESS_BASE_URL|DD_FEATURE_FLAGS_CONFIGURATION_SOURCE_AGENTLESS_EXTRA_HEADERS|FeatureFlagConfigurationSources\\.offline|offline factory" -S products/feature-flagging dd-trace-api internal-api metadata dd-java-agent
result: no matches

[dd-octo-sts]

🟢 Java Benchmark SLOs — All performance SLOs passed

Suite	Status
Startup	🟢 pass

SLO thresholds are defined here based on automatically generated metrics. A warning is raised when results are within 5% of the threshold.

PR vs. master results

Scenario	Candidate	master	Δ (95% CI of mean)
startup:insecure-bank:iast:Agent	13.99 s	13.94 s	[-0.3%; +1.0%] (no difference)
startup:insecure-bank:tracing:Agent	12.84 s	12.97 s	[-1.8%; -0.1%] (maybe better)
startup:petclinic:appsec:Agent	17.06 s	17.35 s	[-6.1%; +2.8%] (no difference)
startup:petclinic:iast:Agent	17.37 s	17.51 s	[-1.6%; +0.1%] (no difference)
startup:petclinic:profiling:Agent	16.77 s	17.34 s	[-7.5%; +0.9%] (no difference)
startup:petclinic:sca:Agent	16.82 s	17.49 s	[-7.9%; +0.2%] (no difference)
startup:petclinic:tracing:Agent	16.51 s	16.63 s	[-1.9%; +0.4%] (no difference)

Commit: e4393c21 · CI Pipeline · Benchmarking Platform UI

---

Load and DaCapo benchmarks can be triggered manually in the GitLab pipeline. Results will appear in the Benchmarking Platform UI after completion.