Added basic Eureka backend and supporting documentation

[jdkeeler]

This adds basic Eureka support as requested in #197, utilizing the hudl/fargo library

[pastjean]

Is there a status of the integration of this feature? Something I'd really like integrated. I can even add tests and help

[wliao008]

LGTM, I would also like to see this get added

[chrisgilbert]

We have some further contributions to this PR - adding of auto metadata population from AWS and the ability to register ELBv2 endpoints if you are using containers in ECS: hudl#2

I am happy to take out a new PR to merge these if it's useful to others. @jdkeeler - these changes might be useful to you anyway. I have tried to preserve your original behaviour if the new flags we added are not set.

[StevenACoffman]

@chrisgilbert hudl#2 seems just what I need. Is there anything remaining to be done, and do you need any help?

[chrisgilbert]

Hi @StevenACoffman - I'm glad it's useful.

ELBv2 registration is working OK in our fork. We've had lots of debates on how to handle it. At the present time it registers the ELB listener endpoint hostname and port as part of the container record, replacing the direct endpoint of the container instead of adding another record for the ELB. That was partly because we had some difficult choices on how to update metadata (we are using that to propagate routes to eureka).

However, we are quite likely to go back to having a separate ELB registration. I am imagining having a flag that will choose whether to keep container registrations, or just hide them if there is a corresponding ELB and only register that.

I'll @ mention you into the next PR we do on it - you can have a look then and see if you can help. Might be next week I hope.