[IMP] Expand env vars in config

[lasley]

• Add optional environment variable expansion for the config file

[coveralls]

Coverage increased (+0.2%) to 89.199% when pulling 50467a3 on LasLabs:feature/yml-env-expansion into 115f7e9 on acsone:master.

[yajo]

Simply great!

[yajo]

Lacks proper docs in README.

[lmignon]

@lasley Thank you for this improvement! As stated by @yajo an entry into the documentation for this new feature will be greatly appreciated.

[lasley]

Oops I knew I was forgetting something! Documentation updated

[coveralls]

Coverage decreased (-0.9%) to 88.153% when pulling 30561dc on LasLabs:feature/yml-env-expansion into 115f7e9 on acsone:master.

[coveralls]

Coverage decreased (-0.9%) to 88.153% when pulling 30561dc on LasLabs:feature/yml-env-expansion into 115f7e9 on acsone:master.

[coveralls]

Coverage decreased (-0.9%) to 88.153% when pulling 30561dc on LasLabs:feature/yml-env-expansion into 115f7e9 on acsone:master.

[lasley]

Coverage drop is due to more lines being added in the ReadMe it seems. I submitted #9 for that.

[lmignon]

@lasley IMO Variable expansion should be the default. A plus should be to keep a parameter to disable the expansion.

[sbidoul]

@lmignon @lasley are there security implications when enabling env var substitution?

[lasley]

@lmignon Making it the default sounds good to me - not being a core contributor to this repo, I was trying to make the change as silently as possible for the proposal.

@sbidoul Yeah there could be some security implications here, as with most things using environment vars. An example of a harmful act that could be performed with this is the using a Travis Secret env var in a test & dumping it to console.

This would require a merge to master though, because the Travis secures are not exposed to forks. I'm sure some other dangerous things could be thought of as well, but that's the main one I watch out for in PRs with systems that include env expansion.

As with most security holes, the tradeoff is usability. In my specific instance, these env vars enhance usability of this application quite a bit in the context of Docker.

[sbidoul]

I prefer to keep the explicit activation of the substitution mode.

[lasley]

Per @pedrobaeza in Tecnativa@50467a3#commitcomment-20682952:

this is an incorrect use of parse arguments.

[pedrobaeza]

Correct use is:

    main_parser.add_argument(
        '-e', '--expand-env',
        dest='expand_env',
        action='store_true',
        help='Expand environment variables in configuration file',
)

[coveralls]

Coverage increased (+0.8%) to 89.803% when pulling a4a8b5a on LasLabs:feature/yml-env-expansion into 115f7e9 on acsone:master.