opentelemetry Connection refused: localhost/0:0:0:0:0:0:0:1:4317 - jaeger

Question

I am using opentelemtry for tracing purpose following are the command but getting error
Can any one suggest what I am doing wrong here:
java -Dotel.traces.exporter=jaeger -Dotel.exporter.jaeger.endpoint=host:14250 -Dotel.resource.attributes=service.name=app-name \
-javaagent:./opentelemetry-javaagent-all.jar -jar app-1.0.0.jar
[opentelemetry.auto.trace 2021-03-17 12:41:19:593 +0530] [IntervalMetricReader-1] WARN io.opentelemetry.exporter.otlp.metrics.OtlpGrpcMetricExporter - Failed to export metrics
io.grpc.StatusRuntimeException: UNAVAILABLE: io exception
at io.grpc.Status.asRuntimeException(Status.java:534)
at io.grpc.stub.ClientCalls$UnaryStreamToFuture.onClose(ClientCalls.java:533)
at io.grpc.internal.ClientCallImpl.closeObserver(ClientCallImpl.java:617)
at io.grpc.internal.ClientCallImpl.access$300(ClientCallImpl.java:70)
at io.grpc.internal.ClientCallImpl$ClientStreamListenerImpl$1StreamClosed.runInternal(ClientCallImpl.java:803)
at io.grpc.internal.ClientCallImpl$ClientStreamListenerImpl$1StreamClosed.runInContext(ClientCallImpl.java:782)
at io.grpc.internal.ContextRunnable.run(ContextRunnable.java:37)
at io.grpc.internal.SerializingExecutor.run(SerializingExecutor.java:123)
at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1128)
at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:628)
at java.base/java.lang.Thread.run(Thread.java:834)
Caused by: io.netty.channel.AbstractChannel$AnnotatedConnectException: Connection refused: localhost/0:0:0:0:0:0:0:1:4317
Caused by: java.net.ConnectException: Connection refused
at java.base/sun.nio.ch.SocketChannelImpl.checkConnect(Native Method)
at java.base/sun.nio.ch.SocketChannelImpl.finishConnect(SocketChannelImpl.java:779)
at io.netty.channel.socket.nio.NioSocketChannel.doFinishConnect(NioSocketChannel.java:330)
at io.netty.channel.nio.AbstractNioChannel$AbstractNioUnsafe.finishConnect(AbstractNioChannel.java:334)
at io.netty.channel.nio.NioEventLoop.processSelectedKey(NioEventLoop.java:702)
at io.netty.channel.nio.NioEventLoop.processSelectedKeysOptimized(NioEventLoop.java:650)
at io.netty.channel.nio.NioEventLoop.processSelectedKeys(NioEventLoop.java:576)
at io.netty.channel.nio.NioEventLoop.run(NioEventLoop.java:493)
at io.netty.util.concurrent.SingleThreadEventExecutor$4.run(SingleThreadEventExecutor.java:989)
at io.netty.util.internal.ThreadExecutorMap$2.run(ThreadExecutorMap.java:74)
at io.netty.util.concurrent.FastThreadLocalRunnable.run(FastThreadLocalRunnable.java:30)
at java.base/java.lang.Thread.run(Thread.java:834)

Answer 1

As far as I understand, OTel has 2 modules - traces and metrics. The error seems to complain about the exports of "metrics", while your traces might actually work fine. It tries to use the default metrics exporter (non jaeger) which writes metrics to a local Otel collector https://github.com/open-telemetry/opentelemetry-collector ( localhost/0:0:0:0:0:0:0:1:4317)
At time of writing, metrics is still marked as Alpha as in https://github.com/open-telemetry/opentelemetry-java/blob/v1.0.1/QUICKSTART.mds
I have not used jaeger perhaps they have support for metrics as well. Try -Dotel.metrics.exporter=jaeger and see whether it works.
If you just want to remove that warning you might consider adding flag -Dotel.metrics.exporter=none which should disable the export of metrics, while traces should still function.