Kafka Schema Registry Unable to Register Schema - Register schema request failed since master is unknown - docker

Question

I have a docker container running the confluentinc/cp-schema-registry:5.5.0 image in AWS Elastic Container Service (Fargate). Only one container is running. API calls to get currently registered schemas through this schema registry are working (e.g. GET http://<schema-registry-url>:8081/subjects). If I try to register a schema that matches a current subject's definition (e.g. POST http://<schema-registry-url>:8081/subjects/<my-subject>/versions) I get the current subject's ID returned. However, if I try to register a brand new subject (e.g. POST http://<schema-registry-url>:8081/subjects/<my-subject-that-doesn't-exist-yet>/versions) I get a 500 exception and a message as follows:
{
"error_code": 50004,
"message": "Master not known."
}
Trying to delete existing schema versions likewise fails. Logs from the docker container show the following:
[2021-01-15 22:09:57,855] ERROR Request Failed with exception (io.confluent.rest.exceptions.DebuggableExceptionMapper)
io.confluent.kafka.schemaregistry.rest.exceptions.RestUnknownMasterException: Master not known.
at io.confluent.kafka.schemaregistry.rest.exceptions.Errors.unknownMasterException(Errors.java:114)
at io.confluent.kafka.schemaregistry.rest.resources.SubjectVersionsResource.register(SubjectVersionsResource.java:281)
at sun.reflect.GeneratedMethodAccessor6.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at org.glassfish.jersey.server.model.internal.ResourceMethodInvocationHandlerFactory.lambda$static$0(ResourceMethodInvocationHandlerFactory.java:52)
at org.glassfish.jersey.server.model.internal.AbstractJavaResourceMethodDispatcher$1.run(AbstractJavaResourceMethodDispatcher.java:124)
at org.glassfish.jersey.server.model.internal.AbstractJavaResourceMethodDispatcher.invoke(AbstractJavaResourceMethodDispatcher.java:167)
at org.glassfish.jersey.server.model.internal.JavaResourceMethodDispatcherProvider$VoidOutInvoker.doDispatch(JavaResourceMethodDispatcherProvider.java:159)
at org.glassfish.jersey.server.model.internal.AbstractJavaResourceMethodDispatcher.dispatch(AbstractJavaResourceMethodDispatcher.java:79)
at org.glassfish.jersey.server.model.ResourceMethodInvoker.invoke(ResourceMethodInvoker.java:469)
at org.glassfish.jersey.server.model.ResourceMethodInvoker.apply(ResourceMethodInvoker.java:391)
at org.glassfish.jersey.server.model.ResourceMethodInvoker.apply(ResourceMethodInvoker.java:80)
at org.glassfish.jersey.server.ServerRuntime$1.run(ServerRuntime.java:253)
at org.glassfish.jersey.internal.Errors$1.call(Errors.java:248)
at org.glassfish.jersey.internal.Errors$1.call(Errors.java:244)
at org.glassfish.jersey.internal.Errors.process(Errors.java:292)
at org.glassfish.jersey.internal.Errors.process(Errors.java:274)
at org.glassfish.jersey.internal.Errors.process(Errors.java:244)
at org.glassfish.jersey.process.internal.RequestScope.runInScope(RequestScope.java:265)
at org.glassfish.jersey.server.ServerRuntime.process(ServerRuntime.java:232)
at org.glassfish.jersey.server.ApplicationHandler.handle(ApplicationHandler.java:680)
at org.glassfish.jersey.servlet.WebComponent.serviceImpl(WebComponent.java:394)
at org.glassfish.jersey.servlet.ServletContainer.serviceImpl(ServletContainer.java:386)
at org.glassfish.jersey.servlet.ServletContainer.doFilter(ServletContainer.java:561)
at org.glassfish.jersey.servlet.ServletContainer.doFilter(ServletContainer.java:502)
at org.glassfish.jersey.servlet.ServletContainer.doFilter(ServletContainer.java:439)
at org.eclipse.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1604)
at org.eclipse.jetty.servlet.ServletHandler.doHandle(ServletHandler.java:545)
at org.eclipse.jetty.server.handler.ScopedHandler.nextHandle(ScopedHandler.java:233)
at org.eclipse.jetty.server.session.SessionHandler.doHandle(SessionHandler.java:1607)
at org.eclipse.jetty.server.handler.ScopedHandler.nextHandle(ScopedHandler.java:233)
at org.eclipse.jetty.server.handler.ContextHandler.doHandle(ContextHandler.java:1297)
at org.eclipse.jetty.server.handler.ScopedHandler.nextScope(ScopedHandler.java:188)
at org.eclipse.jetty.servlet.ServletHandler.doScope(ServletHandler.java:485)
at org.eclipse.jetty.server.session.SessionHandler.doScope(SessionHandler.java:1577)
at org.eclipse.jetty.server.handler.ScopedHandler.nextScope(ScopedHandler.java:186)
at org.eclipse.jetty.server.handler.ContextHandler.doScope(ContextHandler.java:1212)
at org.eclipse.jetty.server.handler.ScopedHandler.handle(ScopedHandler.java:141)
at org.eclipse.jetty.server.handler.HandlerCollection.handle(HandlerCollection.java:146)
at org.eclipse.jetty.server.handler.HandlerCollection.handle(HandlerCollection.java:146)
at org.eclipse.jetty.server.handler.StatisticsHandler.handle(StatisticsHandler.java:173)
at org.eclipse.jetty.server.handler.ContextHandlerCollection.handle(ContextHandlerCollection.java:221)
at org.eclipse.jetty.server.handler.gzip.GzipHandler.handle(GzipHandler.java:767)
at org.eclipse.jetty.server.handler.HandlerWrapper.handle(HandlerWrapper.java:127)
at org.eclipse.jetty.server.Server.handle(Server.java:500)
at org.eclipse.jetty.server.HttpChannel.lambda$handle$1(HttpChannel.java:383)
at org.eclipse.jetty.server.HttpChannel.dispatch(HttpChannel.java:547)
at org.eclipse.jetty.server.HttpChannel.handle(HttpChannel.java:375)
at org.eclipse.jetty.server.HttpConnection.onFillable(HttpConnection.java:270)
at org.eclipse.jetty.io.AbstractConnection$ReadCallback.succeeded(AbstractConnection.java:311)
at org.eclipse.jetty.io.FillInterest.fillable(FillInterest.java:103)
at org.eclipse.jetty.io.ChannelEndPoint$2.run(ChannelEndPoint.java:117)
at org.eclipse.jetty.util.thread.strategy.EatWhatYouKill.runTask(EatWhatYouKill.java:336)
at org.eclipse.jetty.util.thread.strategy.EatWhatYouKill.doProduce(EatWhatYouKill.java:313)
at org.eclipse.jetty.util.thread.strategy.EatWhatYouKill.tryProduce(EatWhatYouKill.java:171)
at org.eclipse.jetty.util.thread.strategy.EatWhatYouKill.run(EatWhatYouKill.java:129)
at org.eclipse.jetty.util.thread.ReservedThreadExecutor$ReservedThread.run(ReservedThreadExecutor.java:388)
at org.eclipse.jetty.util.thread.QueuedThreadPool.runJob(QueuedThreadPool.java:806)
at org.eclipse.jetty.util.thread.QueuedThreadPool$Runner.run(QueuedThreadPool.java:938)
at java.lang.Thread.run(Thread.java:748)
Caused by: io.confluent.kafka.schemaregistry.exceptions.UnknownMasterException: Register schema request failed since master is unknown
at io.confluent.kafka.schemaregistry.storage.KafkaSchemaRegistry.registerOrForward(KafkaSchemaRegistry.java:546)
at io.confluent.kafka.schemaregistry.rest.resources.SubjectVersionsResource.register(SubjectVersionsResource.java:263)
... 59 more
This is in a deployed environment. A local docker container on my machine with the same environment variables as the deployed version will successfully register new schema subjects.

Answer 1

I killed the Task that was running and let the ECS Service spin up a new container and it started to work. I didn't dig into the logs further to see when or where something in the container got corrupted at some point, but at least for now killing and creating a new container did the trick.