feature: add metrics_port from env variable

[ciglenecki]

Extract metrics port from the metrics_port environment variable.

Motivation and Context

There's no reason that the metrics_port is a hard-coded value.

Types of changes

The old code isn't affected since the default value is still 8081

• [x] New feature (non-breaking change which adds functionality)

Checklist:

• [x] My code follows the code style of this project.
• [x] My change requires a change to the documentation.
• [x] I have updated the documentation accordingly.
• [x] I've read the CONTRIBUTION guide
• [x] I have signed-off my commits with git commit -s
• [x] I have added tests to cover my changes.
• [x] All new and existing tests passed.

[derek[bot]]

Thank you for your contribution. unfortunately, one or more of your commits are missing the required "Signed-off-by:" statement. Signing off is part of the Developer Certificate of Origin (DCO) which is used by this project.

Read the DCO and project contributing guide carefully, and amend your commits using the git CLI. Note that this does not require any cryptography, keys or special steps to be taken.

:bulb: Shall we fix this?

This will only take a few moments.

First, clone your fork and checkout this branch using the git CLI.

Next, set up your real name and email address:

git config --global user.name "Your Full Name" git config --global user.email "you@domain.com"

Finally, run one of these commands to add the "Signed-off-by" line to your commits.

If you only have one commit so far then run: git commit --amend --signoff and then git push --force. If you have multiple commits, watch this video.

Check that the message has been added properly by running "git log".

[alexellis]

There's no reason that the metrics_port is a hard-coded value.

There is no reason it should not be hard-coded.

Can you explain why you think we should accept this change? How is it impacting you personally?

And please note, all changes require an issue which needs approval from a maintainer before a PR is sent.

https://github.com/openfaas/faas/blob/master/CONTRIBUTING.md

I'll get this closed until we have an issue and a proper reason for the change beyond "because we can".