Samples listening on 8080 instead of $PORT

[steren]

https://github.com/knative/docs/tree/master/serving/samples/helloworld-go listens on a hardcoded 8080.
But what the Knative runtime contract says is to listen on the port defined by the PORT env var.

[steren]

Others are doing this too, for example, the Ruby one is overriding the PORT env var in the Dockerfile: https://github.com/knative/docs/blob/master/serving/samples/helloworld-ruby/Dockerfile#L11

[steren]

@averikitsch @rgregg let's collaborate on this, using this issue to coordinate

[steren]

CC @grayside

[steren]

@mchmarny @samodell, when reviewing samples, make sure they do not hardcode 8080, as captured in the runtime contract

[averikitsch]

Hello World Samples Reviewed:

• Clojure @josephburnett
• C# @grayside
• Elixir
• Go - @grayside
• Haskell @grayside
• Java
• Node.js - @grayside
• PHP - @grayside
• Python
• Ruby - @averikitsch
• Rust @grayside

[grayside]

Opened a fix for PHP and I have work almost ready for Haskell and C#.

[grayside]

Is this issue limited to helloworld samples or should it encompass updates to ensure $PORT is respected by all samples?

[steren]

Let's keep this issue for the hello world, and open other ones for other samples. Hello world are the highest priority as we want to showcase in a few places.