readme: Update installation instructions

[samuelkarp]

Summary

Updates the installation instructions in the README to be in sync with our documentation. This should help address some confusion (like in #511).

Implementation details

No implementation.

Testing

Followed these instructions on an Ubuntu 14.04 instance.

Description for the changelog

No changelog description

Licensing

This contribution is under the terms of the Apache 2.0 License: yes (Amazon employee)

r? @aaithal @nrdlngr

[jamesongithub]

maybe a ref to the docs, so don't have to worry about keeping them in sync

[samuelkarp]

@jamesongithub There's one right below the "Usage" header, but I think it's helpful to have it here as well.

[aaithal]

[rafaelmagu]

These instructions did not give me a working endpoint inside the container until I accepted all traffic from docker0 with something similar to:

iptables -A INPUT -i docker0 -j ACCEPT

[samuelkarp]

@rafaelmagu That's interesting; can you share more about what system you're running on? The instructions here are the same ones we use in ecs-init for the ECS-optimized AMI.

[rafaelmagu]

We are rolling our own Ubuntu 14.04 AMIs. We have existing iptables rules in place, hence why it got me confused.

We ran this (but with -I) to add the exception right before our REJECT rule.

iptables -A INPUT -i docker0 -p tcp -m tcp --dport 51679 -j ACCEPT

[samuelkarp]

Are the existing iptables rules (the REJECT rule) ones you put in place or ones that were otherwise installed on the hosts? I've used these instructions with the Ubuntu 14.04 AMI in the AWS Marketplace successfully.

[rafaelmagu]

@samuelkarp we put those in place as part of our hardening. Can I suggest the documentation be appended to explain what these rules actually do?

[jamesongithub]

we're on ubuntu 14.04 also , didn't need to change iptables other than the ones in the docs