Add mDns support

[vitorjclima]

What is the current behavior you want to change?

The kurento-media-server docker does not support mDns. Before this solution, the community manually disabled the browser flag, like chrome://flags/#enable-webrtc-hide-local-ips-with-mdns

What is the new behavior provided by this change?

Add mDns support on kurento-media-server docker.

How has this been tested?

It was tested with an IP camera stream in the local network.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature / enhancement (non-breaking change which improves the project)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• My change requires a change to the documentation
• My change requires a change in other repository

Checklist

• I have read the Contribution Guidelines
• I have added an explanation of what the changes do and why they should be included
• I have written new tests for the changes, as applicable, and have successfully run them locally

[j1elo]

Doesn't the first exec replace the bach command by KMS, thus the second exec never gets executed?

[vitorjclima]

@j1elo, you are right, this line is not running and is not necessary, as Avahi runs as a service after installation.

[j1elo]

mDNS is (or was) known to not work correctly inside Docker containers. Does this imply that the Troubleshooting section about mDNS & docker is outdated? Has the situation improved and now mDNS works reliably inside Docker containers?

Caveat: mDNS does not work from within Docker

Docker does not play well with mDNS/zeroconf/Bonjour: resolving .local hostnames from inside containers does not work (easily). […] The reasons run deep into how Docker configures DNS inside a container.

The way to test this is using a WebRTC-to-WebRTC connection (maybe the kurento-hello-world is enough) and see if KMS is really able to resolve the mDNS candidates that Chrome sends.

[jenkinskurento]

Hi there, thanks for your Pull Request!

A Kurento member needs to verify that this patch is reasonable to test. In case it is, they should write a comment with the phrase test this please. Until that is done, I will not automatically test new commits in this PR, but the usual testing commands by Kurento members will still work. Regular contributors can be whitelisted to skip this step.

[jenkinskurento]

Hi there, thanks for your Pull Request!

A Kurento member needs to verify that this patch is reasonable to test. In case it is, they should write a comment with the phrase test this please. Until that is done, I will not automatically test new commits in this PR, but the usual testing commands by Kurento members will still work. Regular contributors can be whitelisted to skip this step.

[vitorjclima]

mDNS is (or was) known to not work correctly inside Docker containers. Does this imply that the Troubleshooting section about mDNS & docker is outdated? Has the situation improved and now mDNS works reliably inside Docker containers?

Caveat: mDNS does not work from within Docker

Docker does not play well with mDNS/zeroconf/Bonjour: resolving .local hostnames from inside containers does not work (easily). […] The reasons run deep into how Docker configures DNS inside a container.

The way to test this is using a WebRTC-to-WebRTC connection (maybe the kurento-hello-world is enough) and see if KMS is really able to resolve the mDNS candidates that Chrome sends.

I saw in the official Kurento Media Server documentation that mDNS does not work properly within docker containers. However, I did several tests, all using docker, and I succeeded in all of these. There were tests using STUN / TURN and the Chrome and Firefox browsers.