[MESOS-7709] Add --default_container_dns flag to the agent.

• Type: Task
• Status: Resolved
• Priority: Major
• Resolution: Fixed
• Fix Version/s: 1.4.0
• Component/s: containerization
• Labels: mesosphere
• Target Version/s: 1.4.0
• Epic Link: IPv6 Support
• Sprint: Mesosphere Sprint 58, Mesosphere Sprint 59, Mesosphere Sprint 60
• Story Points: 5
• Assignee: Qian Zhang
• Reporter: Avinash Sridharan
• Shepherd: Jie Yu
• Created: 22/Jun/17 15:56
• Updated: 03/Aug/17 08:03
• Resolved: 03/Aug/17 08:03

Description

Mesos support both CNI (through `network/cni` isolator) and CNM (through docker) specification. Both these specifications allow for DNS entries for containers to be set on a per-container, and per-network basis.

Currently, the behavior of the agent is to use the DNS nameservers set in /etc/resolv.conf when the CNI or CNM plugin that is used to attached the container to the CNI/CNM network doesnt' explicitly set the DNS for the container. This is a bit inflexible especially when we have a mix of v4 and v6 networks.

The operator should be able to specify DNS nameservers for the networks he installs either the override the ones provided by the plugin or as defaults when the plugins are not going to specify DNS name servers.

In order to achieve the above goal we need to introduce a `--dns` flag to the agent. The `--dns` flag should support a JSON (or a JSON file) with the following schema:

{
  "mesos": [
    {
      "network" : <name of the network>,
      "nameservers": [<list of name servers (upto 3)>]
    }
  ],
  "docker": [
    {
      "network" : <name of the network>,
      "nameservers": [<list of name servers (upto 3)>]
    }
  ]
}