Hello, it seems that the default configuration (when run on Windows 10):

DefaultDockerClientConfig.createDefaultConfigBuilder().build();

is setting the docker host to a unix socket. After the first connection (Apache http 5 transport) this is printed in the console:

15:34:50.030 [main] DEBUG org.apache.hc.client5.http.impl.classic.ConnectExec - ex-0000000001 acquiring connection with route {}->unix://localhost:2375
15:34:50.030 [main] DEBUG org.apache.hc.client5.http.impl.classic.InternalHttpClient - ex-0000000001 acquiring endpoint (3 MINUTES)
15:34:50.031 [main] DEBUG org.apache.hc.client5.http.impl.io.PoolingHttpClientConnectionManager - ex-0000000001 endpoint lease request (3 MINUTES) [route: {}->unix://localhost:2375][total available: 0; route allocated: 0 of 100; total allocated: 0 of 100]
15:34:50.036 [main] DEBUG org.apache.hc.client5.http.impl.io.PoolingHttpClientConnectionManager - ex-0000000001 endpoint leased [route: {}->unix://localhost:2375][total available: 0; route allocated: 1 of 100; total allocated: 1 of 100]
15:34:50.046 [main] DEBUG org.apache.hc.client5.http.impl.io.PoolingHttpClientConnectionManager - ex-0000000001 acquired ep-0000000000
15:34:50.047 [main] DEBUG org.apache.hc.client5.http.impl.classic.InternalHttpClient - ex-0000000001 acquired endpoint ep-0000000000
15:34:50.047 [main] DEBUG org.apache.hc.client5.http.impl.classic.ConnectExec - ex-0000000001 opening connection {}->unix://localhost:2375
15:34:50.047 [main] DEBUG org.apache.hc.client5.http.impl.classic.InternalHttpClient - ep-0000000000 connecting endpoint (30000000000 NANOSECONDS)
15:34:50.048 [main] DEBUG org.apache.hc.client5.http.impl.io.PoolingHttpClientConnectionManager - ep-0000000000 connecting endpoint to unix://localhost:2375 (30000000000 NANOSECONDS)
Exception in thread "main" java.lang.UnsatisfiedLinkError: Error looking up function 'write': Die angegebene Prozedur wurde nicht gefunden.

("Die angegebene Prozedur wurde nicht gefunden" ~ "Procedure not found")

As you can see, there are entries like route: {}->unix://localhost:2375.

When I explicitly define the config like this, it is connecting successfully:

DefaultDockerClientConfig.createDefaultConfigBuilder() .withDockerHost("tcp://localhost:2375") .withDockerTlsVerify(false) .build();

I have created an small example on GitHub, which can be build with Maven. I used Java 14 in this case, which can be change in pom.xml.

Any info appreciated, thank you!