Switch to using hyphens as a separator in hostnames

[kung-foo]

The hostname format used by fig creates names that are not strictly valid.

Current pseudo-code:

name = '_'.join([project, container, instance_num])

This generates names like cluster_hadoop_1. Underscores are not valid (though in practice most components are tolerant of this).

Valid names should match [a-zA-Z0-9\-]+.

I came across this error when trying to test out some hadoop/hdfs containers and hadoop bailed with an exception saying that hdfs://flume_hadoop_1/ was not valid URI (even though it was in /etc/hosts and ping flume_hadoop_1 worked just fine).

See: http://en.wikipedia.org/wiki/Hostname#Restrictions_on_valid_host_names

Changing this to dashes is easy, but it would break existing configurations that depend on hard coded container names.

[kung-foo]

also see: moby/moby#5418

[danburkert]

This is causing pain for me as well, in pretty much the exact same scenario (the hostname being parsed by Java's standard library URI parser). Is this a fig issue, or should it be fixed in docker?

[aanand]

Frustratingly, underscores are invalid in hostnames, and dashes are invalid in shell variable names. So if you can't name a Docker link without either breaking one of those or smushing everything together (e.g. hadoop1). Not ideal.

However, looks like moby/moby#6270 might fix this by sanitising environment variable names, in which case Fig can switch to dashes and everything will hopefully work:

web:
  links:
    - hadoop

$ fig run web cat /etc/hosts
...
172.17.0.42 hadoop-1
...

$ fig run web env
...
HADOOP_1_PORT=tcp://172.17.0.42:5432
HADOOP_1_PORT_5432_TCP=tcp://172.17.0.42:5432
HADOOP_1_PORT_5432_TCP_ADDR=172.17.0.42
...

[aanand]

#349 is also relevant.

[nubs]

Technically speaking, I don't believe that hyphens in shell variable names are strictly forbidden. You just can't access them in the normal way:

$ env foo-bar=baz bash
$ printenv foo-bar
baz

[bfirsh]

👍 switching to hyphens

[zeevallin]

What about writing both hyphenated and underscored to the hosts file for now?

[aanand]

@zeeraw that would be out of fig's scope - a job for docker itself.