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flagd can expose a gRPC sync service, allowing in-process providers to obtain their flag definitions. The gRPC sync stream contains flag definitions currently configured at flagd as sync-configurations.

title: gRPC sync
    flagd ||--o{ "sync (file)" : watches
    flagd ||--o{ "sync (http)" : polls
    flagd ||--o{ "sync (grpc)" : "sync.proto (gRPC/stream)"
    flagd ||--o{ "sync (kubernetes)" : watches
    "In-Process provider" ||--|| flagd : "gRPC sync stream (default port 8015)"

You may change the default port of the service using startup flag --sync-port (or -g shothand flag).

By default, the gRPC stream exposes all the flag configurations, with conflicting flag keys merged following flag's standard merge strategy. You can read more about the merge strategy in our dedicated concepts guide on syncs.

If you specify a selector in the gRPC sync request, the gRPC service will attempt match the provided selector value to a source, and stream just the flags identified in that source. For example, if selector is set to myFlags.json, service will stream flags observed from myFlags.json file. Note that, to observe flags from myFlags.json file, you may use startup option uri like --uri myFlags.json or source option --sources='[{"uri":"myFlags.json", provider":"file"}]. And the request will fail if there is no flag source matching the requested selector.

flagd provider implementations expose the ability to define the selector value. Please consider below example for Java,

final FlagdProvider flagdProvider =
        new FlagdProvider(FlagdOptions.builder()