[Bug]:

Module

Core

Testcontainers version

1.21.0

Using the latest Testcontainers version?

Yes

Host OS

Windows 11 + WSL2(Ubuntu)

Host Arch

X86

Docker version

Client: Docker Engine - Community
 Version:           28.1.1
 API version:       1.49
 Go version:        go1.23.8
 Git commit:        4eba377
 Built:             Fri Apr 18 09:52:14 2025
 OS/Arch:           linux/amd64
 Context:           default

Server: Docker Engine - Community
 Engine:
  Version:          28.1.1
  API version:      1.49 (minimum version 1.24)
  Go version:       go1.23.8
  Git commit:       01f442b
  Built:            Fri Apr 18 09:52:14 2025
  OS/Arch:          linux/amd64
  Experimental:     false
 containerd:
  Version:          1.7.27
  GitCommit:        05044ec0a9a75232cad458027ca83437aae3f4da
 runc:
  Version:          1.2.5
  GitCommit:        v1.2.5-0-g59923ef
 docker-init:
  Version:          0.19.0
  GitCommit:        de40ad0

What happened?

This code in RyukResourceReaper :

    @SneakyThrows(InterruptedException.class)
    private synchronized void maybeStart() {
        ...
        ...
        Thread kiraThread = new Thread(
            DockerClientFactory.TESTCONTAINERS_THREAD_GROUP,
            () -> {
                while (true) {
                    RYUK_ACK_RATE_LIMITER.doWhenReady(() -> {
                        int index = 0;
                        // not set the read timeout, as Ryuk would not send anything unless a new filter is submitted, meaning that we would get a timeout exception pretty quick
                        try (Socket clientSocket = new Socket()) {
                            clientSocket.connect(new InetSocketAddress(host, ryukPort), 5 * 1000);
                            ResourceReaper.FilterRegistry registry = new ResourceReaper.FilterRegistry(
                                clientSocket.getInputStream(),
                                clientSocket.getOutputStream()
                            );

                            synchronized (ResourceReaper.DEATH_NOTE) {
                                while (true) {
                                    if (ResourceReaper.DEATH_NOTE.size() <= index) {
                                        try {
                                            ResourceReaper.DEATH_NOTE.wait(1_000);
                                            continue;
                                        } catch (InterruptedException e) {
                                            throw new RuntimeException(e);
                                        }
                                    }
                                    List<Map.Entry<String, String>> filters = ResourceReaper.DEATH_NOTE.get(index);
                                    boolean isAcknowledged = registry.register(filters);
                                    if (isAcknowledged) {
                                        log.debug("Received 'ACK' from Ryuk");
                                        ryukScheduledLatch.countDown();
                                        index++;
                                    } else {
                                        log.debug("Didn't receive 'ACK' from Ryuk. Will retry to send filters.");
                                    }
                                }
                            }
                        } catch (IOException e) {
                            log.warn("Can not connect to Ryuk at {}:{}", host, ryukPort, e);
                        }
                    });
                }
            },
            "testcontainers-ryuk"
        );

The problem is the line:

/log.warn("Can not connect to Ryuk at {}:{}", host, ryukPort, e);

Why?

It shouldn't be a warning since it is expected that this can happen. The situation fixes itself after 4-500 msecs (on my host).
IMO, warnings are for unexpected events or for things that requires the user's attention. This is logged with stack trace and all .. but it is really not something the user should be concerned with.

I suggest the following instead

/log.info("Attempt failed: Cannot connect to Ryuk at {}:{}. Will retry", host, ryukPort);

.. or something.

Relevant log output

13:35:24.175 [main] INFO tc.testcontainers/ryuk:0.11.0 -- Container testcontainers/ryuk:0.11.0 started in PT0.4782861S
13:35:24.179 [testcontainers-ryuk] WARN org.testcontainers.utility.RyukResourceReaper -- Can not connect to Ryuk at localhost:32790
java.net.ConnectException: Connection refused: getsockopt
	at java.base/sun.nio.ch.Net.pollConnect(Native Method)
	at java.base/sun.nio.ch.Net.pollConnectNow(Net.java:628)
	at java.base/sun.nio.ch.NioSocketImpl.timedFinishConnect(NioSocketImpl.java:533)
	at java.base/sun.nio.ch.NioSocketImpl.connect(NioSocketImpl.java:583)
	at java.base/java.net.SocksSocketImpl.connect(SocksSocketImpl.java:282)
	at java.base/java.net.Socket.connect(Socket.java:665)
	at org.testcontainers.utility.RyukResourceReaper.lambda$maybeStart$0(RyukResourceReaper.java:92)
	at org.rnorth.ducttape.ratelimits.RateLimiter.doWhenReady(RateLimiter.java:27)
	at org.testcontainers.utility.RyukResourceReaper.lambda$maybeStart$1(RyukResourceReaper.java:88)
	at java.base/java.lang.Thread.run(Thread.java:1447)
13:35:24.432 [testcontainers-ryuk] WARN org.testcontainers.utility.RyukResourceReaper -- Can not connect to Ryuk at localhost:32790
java.net.ConnectException: Connection refused: getsockopt
	at java.base/sun.nio.ch.Net.pollConnect(Native Method)
	at java.base/sun.nio.ch.Net.pollConnectNow(Net.java:628)
	at java.base/sun.nio.ch.NioSocketImpl.timedFinishConnect(NioSocketImpl.java:533)
	at java.base/sun.nio.ch.NioSocketImpl.connect(NioSocketImpl.java:583)
	at java.base/java.net.SocksSocketImpl.connect(SocksSocketImpl.java:282)
	at java.base/java.net.Socket.connect(Socket.java:665)
	at org.testcontainers.utility.RyukResourceReaper.lambda$maybeStart$0(RyukResourceReaper.java:92)
	at org.rnorth.ducttape.ratelimits.RateLimiter.doWhenReady(RateLimiter.java:27)
	at org.testcontainers.utility.RyukResourceReaper.lambda$maybeStart$1(RyukResourceReaper.java:88)
	at java.base/java.lang.Thread.run(Thread.java:1447)
13:35:24.688 [main] INFO org.testcontainers.utility.RyukResourceReaper -- Ryuk started - will monitor and terminate Testcontainers containers on JVM exit
13:

Additional Information

No response

Start in RyukResourceReaper.maybeStart at the connection-failure log shown in the issue. Review the surrounding retry behavior and relevant Core tests, then verify that expected connection retries no longer produce warning-level stack traces while Ryuk still starts and registers resources normally.