Study what restrictions about creating local files on containers are

[xni]

I think I'll be great if a container will be able to create some files, independent and secure from other running containers on the same node. I think, this can be done. Creating temporary per-container folders will allow us to use them for docker shared volumes (http://docs.docker.com/userguide/dockervolumes/#mount-a-host-directory-as-a-data-volume) to store a temporary result.

[xni]

I haven't faced with any problems on file creation.

This is my changes in MyContainer.java:

private void run() throws IOException {
  LOG.info("Running Container on {}", this.hostname);
  // http://stackoverflow.com/questions/617414/create-a-temporary-directory-in-java
  final File temp;
  final File parent_dir = new File("/opt/docker-output");
  temp = File.createTempFile("docker-", null, parent_dir);
  temp.delete();
  temp.mkdir();
  final File output = new File(temp, "output.txt");
  FileWriter fr = new FileWriter(output);
  fr.write("Test: ok!");
  fr.close();
}

Then I performed

$ sudo mkdir /opt/docker-output
$ sudo chown yarn /opt/docker-output
$ sudo chgrp yarn /opt/docker-output

on nodes.

Result:

$ head /opt/docker-output/*/output.txt
==> /opt/docker-output/docker-253786542757618065.tmp/output.txt <==
Test: ok!
==> /opt/docker-output/docker-3370875717565256190.tmp/output.txt <==
Test: ok!
==> /opt/docker-output/docker-5835337523467844749.tmp/output.txt <==
Test: ok!
==> /opt/docker-output/docker-8378056582861110864.tmp/output.txt <==
Test: ok!
==> /opt/docker-output/docker-8617089359044222916.tmp/output.txt <==
Test: ok!

[xni]

I don't know how files are created without extra directory creation (/opt/docker-output), but it's okay in the moment to use this approach.