Strange connection issue (Unable to connect)

[Obyvante]

I have two different applications and they use the same API I coded. Both applications call api.connectRedis(). Same code, same IP address, and same port but for some reason, one application cannot connect to the Redis server.

Everything works perfectly fine when I try this on my personal computer; macOS Sonoma.

This is so strange and it is hard to explain why. Any idea why it is happening even though everything is the same?

Connection Code

// Client and connection initialization.
this.client = RedisClient.create(RedisURI.builder()
    .withHost(this.host)
    .withPort(this.port)
    .withPassword(redisInformation.password().toCharArray())
    .build());

// Base client connection.
// One connection is enough for everything.
this.connection = this.client.connect(codec);
this.connection.addListener(BaseRedisProvider.STATE_HANDLER);

Error code

Caused by: io.lettuce.core.RedisConnectionException: Unable to connect to localhost/<unresolved>:6379

Tests

Redis-cli: Connected, everything is fine and one application connects without any problem.

Specs

OS: Debian 12
Redis server: Docker image -> redis:7.2.1 -> port exposed to outside and works perfectly fine.

[mp911de]

Unable to connect to localhost/<unresolved>:6379 has much more stack trace. Can you include the cause?

[mp911de]

There must be more than io.lettuce.core.RedisConnectionException: Unable to connect to 127.0.0.1/<unresolved>:6379 as the cause is a netty exception.

[Obyvante]

This is the full exception error, sorry. Do you want me to check something else to debug so I can provide you with more information?

[Obyvante]

For the sake of clarification and OS tests, I have tried other Redis libraries to ensure it is not related to anything like the Java version, OS, etc.

The tests were successful and all of them worked. Lettuce has a problem with working on different OS.

[Obyvante]

More error log;

[09:53:33 INFO] [main]: [LoggedPrintStream] [STDERR]: io.lettuce.core.RedisConnectionException: Unable to connect to localhost/<unresolved>:6379
[09:53:33 INFO] [main]: [LoggedPrintStream] [STDERR]: 	at io.lettuce.core.RedisConnectionException.create(RedisConnectionException.java:78)
[09:53:33 INFO] [main]: [LoggedPrintStream] [STDERR]: 	at io.lettuce.core.RedisConnectionException.create(RedisConnectionException.java:56)
[09:53:33 INFO] [main]: [LoggedPrintStream] [STDERR]: 	at io.lettuce.core.AbstractRedisClient.getConnection(AbstractRedisClient.java:350)
[09:53:33 INFO] [main]: [LoggedPrintStream] [STDERR]: 	at io.lettuce.core.RedisClient.connect(RedisClient.java:215)
[09:53:33 INFO] [main]: [LoggedPrintStream] [STDERR]: 	at io.lettuce.core.RedisClient.connect(RedisClient.java:200)
[09:53:33 INFO] [main]: [LoggedPrintStream] [STDERR]: 	at com.atlas.api.service.content.database.DatabaseService.<init>(DatabaseService.java:75)
[09:53:33 INFO] [main]: [LoggedPrintStream] [STDERR]: 	at java.base/jdk.internal.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
[09:53:33 INFO] [main]: [LoggedPrintStream] [STDERR]: 	at java.base/jdk.internal.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:77)
[09:53:33 INFO] [main]: [LoggedPrintStream] [STDERR]: 	at java.base/jdk.internal.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
[09:53:33 INFO] [main]: [LoggedPrintStream] [STDERR]: 	at java.base/java.lang.reflect.Constructor.newInstanceWithCaller(Constructor.java:499)
[09:53:33 INFO] [main]: [LoggedPrintStream] [STDERR]: 	at java.base/java.lang.reflect.Constructor.newInstance(Constructor.java:480)
[09:53:33 INFO] [main]: [LoggedPrintStream] [STDERR]: 	at com.atlas.api.Atlas.registerService(Atlas.java:289)
[09:53:33 INFO] [main]: [LoggedPrintStream] [STDERR]: 	at com.atlas.api.Atlas.registerServices(Atlas.java:240)
[09:53:33 INFO] [main]: [LoggedPrintStream] [STDERR]: 	at com.atlas.api.Atlas.<init>(Atlas.java:106)
[09:53:33 INFO] [main]: [LoggedPrintStream] [STDERR]: 	at com.atlas.fabric.AtlasFabric.<init>(AtlasFabric.java:60)
[09:53:33 INFO] [main]: [LoggedPrintStream] [STDERR]: 	at java.base/jdk.internal.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
[09:53:33 INFO] [main]: [LoggedPrintStream] [STDERR]: 	at java.base/jdk.internal.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:77)
[09:53:33 INFO] [main]: [LoggedPrintStream] [STDERR]: 	at java.base/jdk.internal.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
[09:53:33 INFO] [main]: [LoggedPrintStream] [STDERR]: 	at java.base/java.lang.reflect.Constructor.newInstanceWithCaller(Constructor.java:499)
[09:53:33 INFO] [main]: [LoggedPrintStream] [STDERR]: 	at java.base/java.lang.reflect.Constructor.newInstance(Constructor.java:480)
[09:53:33 INFO] [main]: [LoggedPrintStream] [STDERR]: 	at net.fabricmc.loader.impl.util.DefaultLanguageAdapter.create(DefaultLanguageAdapter.java:58)
[09:53:33 INFO] [main]: [LoggedPrintStream] [STDERR]: 	at net.fabricmc.loader.impl.entrypoint.EntrypointStorage$NewEntry.getOrCreate(EntrypointStorage.java:117)
[09:53:33 INFO] [main]: [LoggedPrintStream] [STDERR]: 	at net.fabricmc.loader.impl.entrypoint.EntrypointContainerImpl.getEntrypoint(EntrypointContainerImpl.java:53)
[09:53:33 INFO] [main]: [LoggedPrintStream] [STDERR]: 	at net.fabricmc.loader.impl.entrypoint.EntrypointUtils.invoke0(EntrypointUtils.java:47)
[09:53:33 INFO] [main]: [LoggedPrintStream] [STDERR]: 	at net.fabricmc.loader.impl.entrypoint.EntrypointUtils.invoke(EntrypointUtils.java:35)
[09:53:33 INFO] [main]: [LoggedPrintStream] [STDERR]: 	at net.fabricmc.loader.impl.game.minecraft.Hooks.startServer(Hooks.java:62)
[09:53:33 INFO] [main]: [LoggedPrintStream] [STDERR]: 	at net.minecraft.server.Main.main(Main.java:112)
[09:53:33 INFO] [main]: [LoggedPrintStream] [STDERR]: 	at net.fabricmc.loader.impl.game.minecraft.MinecraftGameProvider.launch(MinecraftGameProvider.java:468)
[09:53:33 INFO] [main]: [LoggedPrintStream] [STDERR]: 	at net.fabricmc.loader.impl.launch.knot.Knot.launch(Knot.java:74)
[09:53:33 INFO] [main]: [LoggedPrintStream] [STDERR]: 	at net.fabricmc.loader.impl.launch.knot.KnotServer.main(KnotServer.java:23)
[09:53:33 INFO] [main]: [LoggedPrintStream] [STDERR]: 	at net.fabricmc.loader.impl.launch.server.FabricServerLauncher.main(FabricServerLauncher.java:69)
[09:53:33 INFO] [main]: [LoggedPrintStream] [STDERR]: 	at net.fabricmc.installer.ServerLauncher.main(ServerLauncher.java:69)
[09:53:33 INFO] [main]: [LoggedPrintStream] [STDERR]: Caused by: java.lang.UnsatisfiedLinkError: 'int io.netty.channel.unix.ErrorsStaticallyReferencedJniMethods.errorEHOSTUNREACH()'
[09:53:33 INFO] [main]: [LoggedPrintStream] [STDERR]: 	at io.netty.channel.unix.ErrorsStaticallyReferencedJniMethods.errorEHOSTUNREACH(Native Method)
[09:53:33 INFO] [main]: [LoggedPrintStream] [STDERR]: 	at io.netty.channel.unix.Errors.<clinit>(Errors.java:62)
[09:53:33 INFO] [main]: [LoggedPrintStream] [STDERR]: 	at io.netty.channel.unix.Socket.connect(Socket.java:351)
[09:53:33 INFO] [main]: [LoggedPrintStream] [STDERR]: 	at io.netty.channel.epoll.AbstractEpollChannel.doConnect0(AbstractEpollChannel.java:773)
[09:53:33 INFO] [main]: [LoggedPrintStream] [STDERR]: 	at io.netty.channel.epoll.EpollSocketChannel.doConnect0(EpollSocketChannel.java:144)
[09:53:33 INFO] [main]: [LoggedPrintStream] [STDERR]: 	at io.netty.channel.epoll.AbstractEpollChannel.doConnect(AbstractEpollChannel.java:758)
[09:53:33 INFO] [main]: [LoggedPrintStream] [STDERR]: 	at io.netty.channel.epoll.AbstractEpollChannel$AbstractEpollUnsafe.connect(AbstractEpollChannel.java:600)
[09:53:33 INFO] [main]: [LoggedPrintStream] [STDERR]: 	at io.netty.channel.DefaultChannelPipeline$HeadContext.connect(DefaultChannelPipeline.java:1342)
[09:53:33 INFO] [main]: [LoggedPrintStream] [STDERR]: 	at io.netty.channel.AbstractChannelHandlerContext.invokeConnect(AbstractChannelHandlerContext.java:653)
[09:53:33 INFO] [main]: [LoggedPrintStream] [STDERR]: 	at io.netty.channel.AbstractChannelHandlerContext.connect(AbstractChannelHandlerContext.java:632)
[09:53:33 INFO] [main]: [LoggedPrintStream] [STDERR]: 	at io.netty.channel.AbstractChannelHandlerContext.connect(AbstractChannelHandlerContext.java:616)
[09:53:33 INFO] [main]: [LoggedPrintStream] [STDERR]: 	at io.netty.channel.DefaultChannelPipeline.connect(DefaultChannelPipeline.java:978)
[09:53:33 INFO] [main]: [LoggedPrintStream] [STDERR]: 	at io.netty.channel.AbstractChannel.connect(AbstractChannel.java:265)
[09:53:33 INFO] [main]: [LoggedPrintStream] [STDERR]: 	at io.netty.bootstrap.Bootstrap$3.run(Bootstrap.java:264)
[09:53:33 INFO] [main]: [LoggedPrintStream] [STDERR]: 	at io.netty.util.concurrent.AbstractEventExecutor.runTask(AbstractEventExecutor.java:173)
[09:53:33 INFO] [main]: [LoggedPrintStream] [STDERR]: 	at io.netty.util.concurrent.AbstractEventExecutor.safeExecute(AbstractEventExecutor.java:166)
[09:53:33 INFO] [main]: [LoggedPrintStream] [STDERR]: 	at io.netty.util.concurrent.SingleThreadEventExecutor.runAllTasks(SingleThreadEventExecutor.java:470)
[09:53:33 INFO] [main]: [LoggedPrintStream] [STDERR]: 	at io.netty.channel.epoll.EpollEventLoop.run(EpollEventLoop.java:406)
[09:53:33 INFO] [main]: [LoggedPrintStream] [STDERR]: 	at io.netty.util.concurrent.SingleThreadEventExecutor$4.run(SingleThreadEventExecutor.java:997)
[09:53:33 INFO] [main]: [LoggedPrintStream] [STDERR]: 	at io.netty.util.internal.ThreadExecutorMap$2.run(ThreadExecutorMap.java:74)
[09:53:33 INFO] [main]: [LoggedPrintStream] [STDERR]: 	at io.netty.util.concurrent.FastThreadLocalRunnable.run(FastThreadLocalRunnable.java:30)
[09:53:33 INFO] [main]: [LoggedPrintStream] [STDERR]: 	at java.base/java.lang.Thread.run(Thread.java:840)

[mp911de]

There can be a multitude of reasons, ranging from library incompatibilities up to native library failures. Without the cause, we cannot proceed in diagnosis.

Line AbstractRedisClient.java:350 catches some sort of exception and wraps it into RedisConnectionException.

[mp911de]

Ah, here we go:

[09:53:33 INFO] [main]: [LoggedPrintStream] [STDERR]: Caused by: java.lang.UnsatisfiedLinkError: 'int io.netty.channel.unix.ErrorsStaticallyReferencedJniMethods.errorEHOSTUNREACH()'

You're having the epoll dependency on your class path and the error indicates a missing symbol. I suspect a glibc incompatibility although I'm not fully sure.

What you can do is either:

1. excluding the netty-transport-native-epoll dependency
2. Setting a system property -Dio.lettuce.core.epoll=false to instruct Lettuce to not use the epoll native transport
3. Upgrade or downgrade netty according to your system baseline.

[mp911de]

See also netty/netty#13447

[Obyvante]

Both solutions have worked for me.

@mp911de Thank you so much for your fast and clear solution!

[Obyvante]

Sorry for bumping this discussion again even if it is solved!

Since I am using an external application and use my API with it, I cannot exclude netty-transport-native-epoll and -Dio.lettuce.core.epoll=false.

The last option for me seems Upgrade or downgrade netty according to your system baseline.. The base application I have is using netty 4.1.82.Final. How should I handle/depend lettuce for this project. Do you suggest me to exclude netty from lettuce-core?

EDIT I have fixed this issue as well by completely excluding netty module since my application's netty versions all different. With this, the whole problem has solved. You may start testing by excluding netty-transport-native-epoll as mp911de stated then move one completely excluding the module.