firebase database 테스트 중 아래와 같은 오류가 발생하면..
com.google.api.gax.rpc.UnavailableException: io.grpc.StatusRuntimeException: UNAVAILABLE: Credentials failed to obtain metadata at com.google.api.gax.rpc.ApiExceptionFactory.createException(ApiExceptionFactory.java:69) at com.google.api.gax.grpc.GrpcApiExceptionFactory.create(GrpcApiExceptionFactory.java:72) at com.google.api.gax.grpc.GrpcApiExceptionFactory.create(GrpcApiExceptionFactory.java:60) at com.google.api.gax.grpc.GrpcExceptionCallable$ExceptionTransformingFuture.onFailure(GrpcExceptionCallable.java:97) at com.google.api.core.ApiFutures$1.onFailure(ApiFutures.java:68) at com.google.common.util.concurrent.Futures$CallbackListener.run(Futures.java:982) at com.google.common.util.concurrent.DirectExecutor.execute(DirectExecutor.java:30) at com.google.common.util.concurrent.AbstractFuture.executeListener(AbstractFuture.java:1138) at com.google.common.util.concurrent.AbstractFuture.complete(AbstractFuture.java:957) at com.google.common.util.concurrent.AbstractFuture.setException(AbstractFuture.java:748) at io.grpc.stub.ClientCalls$GrpcFuture.setException(ClientCalls.java:522) at io.grpc.stub.ClientCalls$UnaryStreamToFuture.onClose(ClientCalls.java:497) at io.grpc.PartialForwardingClientCallListener.onClose(PartialForwardingClientCallListener.java:39) at io.grpc.ForwardingClientCallListener.onClose(ForwardingClientCallListener.java:23) at io.grpc.ForwardingClientCallListener$SimpleForwardingClientCallListener.onClose(ForwardingClientCallListener.java:40) at io.grpc.internal.CensusStatsModule$StatsClientInterceptor$1$1.onClose(CensusStatsModule.java:700) at io.grpc.PartialForwardingClientCallListener.onClose(PartialForwardingClientCallListener.java:39) at io.grpc.ForwardingClientCallListener.onClose(ForwardingClientCallListener.java:23) at io.grpc.ForwardingClientCallListener$SimpleForwardingClientCallListener.onClose(ForwardingClientCallListener.java:40) at io.grpc.internal.CensusTracingModule$TracingClientInterceptor$1$1.onClose(CensusTracingModule.java:399) at io.grpc.internal.ClientCallImpl.closeObserver(ClientCallImpl.java:510) at io.grpc.internal.ClientCallImpl.access$300(ClientCallImpl.java:66) at io.grpc.internal.ClientCallImpl$ClientStreamListenerImpl.close(ClientCallImpl.java:630) at io.grpc.internal.ClientCallImpl$ClientStreamListenerImpl.access$700(ClientCallImpl.java:518) at io.grpc.internal.ClientCallImpl$ClientStreamListenerImpl$1StreamClosed.runInternal(ClientCallImpl.java:692) at io.grpc.internal.ClientCallImpl$ClientStreamListenerImpl$1StreamClosed.runInContext(ClientCallImpl.java:681) at io.grpc.internal.ContextRunnable.run(ContextRunnable.java:37) at io.grpc.internal.SerializingExecutor.run(SerializingExecutor.java:123) at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511) at java.util.concurrent.FutureTask.run(FutureTask.java:266) at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.access$201(ScheduledThreadPoolExecutor.java:180) at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.run(ScheduledThreadPoolExecutor.java:293) at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142) at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617) at java.lang.Thread.run(Thread.java:745)
* 서버의 시간을 확인 해본다.
잘못 되어 있으면 수정하면 동작할 수 있다.