Codeship builds fail: `can not connect to Ryuk`

TestContainers works locally. Builds on Codeship fail with the following:

2018-02-10_19:22:35.027 WARN  o.t.utility.ResourceReaper - Can not connect to Ryuk at 172.17.0.1:32768
java.net.SocketException: Broken pipe (Write failed)
	at java.net.SocketOutputStream.socketWrite0(Native Method)
	at java.net.SocketOutputStream.socketWrite(SocketOutputStream.java:111)
	at java.net.SocketOutputStream.write(SocketOutputStream.java:134)
	at org.testcontainers.utility.ResourceReaper.lambda$start$2(ResourceReaper.java:136)
	at java.lang.Thread.run(Thread.java:748)
2018-02-10_19:22:35.044 WARN  o.t.utility.ResourceReaper - Can not connect to Ryuk at 172.17.0.1:32768
java.net.SocketException: Connection reset
	at java.net.SocketInputStream.read(SocketInputStream.java:210)
	at java.net.SocketInputStream.read(SocketInputStream.java:141)
	at sun.nio.cs.StreamDecoder.readBytes(StreamDecoder.java:284)
	at sun.nio.cs.StreamDecoder.implRead(StreamDecoder.java:326)
	at sun.nio.cs.StreamDecoder.read(StreamDecoder.java:178)
	at java.io.InputStreamReader.read(InputStreamReader.java:184)
	at java.io.BufferedReader.fill(BufferedReader.java:161)
	at java.io.BufferedReader.readLine(BufferedReader.java:324)
	at java.io.BufferedReader.readLine(BufferedReader.java:389)
	at org.testcontainers.utility.ResourceReaper.lambda$start$2(ResourceReaper.java:139)
	at java.lang.Thread.run(Thread.java:748)

I do not use volume mapping for this service, but I use volumes to build other services. My understanding of https://www.testcontainers.org/usage/inside_docker.html is that I do not need to mount the Docker socket volume.

I've set add_docker: true in my codeship-services.yml, which does the following:

Add the environment variables DOCKER_HOST, DOCKER_TLS_VERIFY and DOCKER_CERT_PATH from the host.
If DOCKER_CERT_PATH is set, it will mount the certificate directory through to the container. See add_docker for an example using Docker-in-Docker.

https://documentation.codeship.com/pro/builds-and-configuration/services/

Beginne mit dem Stacktrace von ResourceReaper und der inside-Docker-Dokumentation von Testcontainers und untersuche anschließend, wie die add_docker-Einstellung von Codeship DOCKER_HOST, DOCKER_TLS_VERIFY, DOCKER_CERT_PATH und Zertifikate bereitstellt. Reproduziere den Ryuk-Verbindungsfehler in der gemeldeten Codeship-Konfiguration; abgeschlossen ist die Aufgabe, wenn die Konfigurationsursache identifiziert und die unterstützte Lösung dokumentiert oder implementiert wurde.