netdog: Persist current IP and add subcommand node-ip for retrieval

[zmrow]

Issue number:
Related to #1458

Description of changes:

With this change, netdog will persist the node's current IP (read from
it's DHCP leases file) to /var/lib/netdog/current_ip.  It does this as
part of its "install" subcommand, which is run each time that wickedd
receives an update.  A new subcommand has also been added, which
retrieves the current IP from said file and returns it as JSON.  This
subcommand is intended for use as a settings generator.

This change is meant to support the VMWare variant #1451, specifically the kubernetes.node-ip setting and will receive further exercise with that PR.

Testing done:

• Build and run an aws-dev variant to ensure that the file containing the IP exists with the correct data and the subcommand works:

bash-5.0# ls -lahZ /var/lib/netdog/current_ip 
-rw-r--r--. 1 root root system_u:object_r:lease_t:s0 11 Apr 19 20:15 /var/lib/netdog/current_ip

bash-5.0# cat /var/lib/netdog/current_ip 
10.0.60.220

bash-5.0# netdog node-ip
"10.0.60.220"

• Build and run an aws-k8s-1.19 node, started sheltie and checked files. Node joins the cluster just fine and I can run pods on it.

Terms of contribution:

By submitting this pull request, I agree that this contribution is dual-licensed under the terms of both the Apache License, version 2.0, and the MIT license.

[bcressey]

Can you also verify that /etc/resolv.conf and /proc/sys/kernel/hostname are still set correctly?

[bcressey]

I expect it'd work with just this change to Cargo.lock and not all the rest of it. Can you try that?

[webern]

Was this a cargo update?

[zmrow]

It wasn't meant to be. I'm going to implement @bcressey 's ask above to avoid it.

[bcressey]

nit: this might be clearer overall, since it doesn't mix NodeIp in with the handling of Install and Remove:

Suggested change

	match parse_args(env::args())? {
	(SubCommand::NodeIp, None) => node_ip()?,
	(subcommand, Some(args)) => match subcommand {
	SubCommand::Install => install(&args)?,
	SubCommand::Remove => remove(&args)?,
	SubCommand::NodeIp => {
	usage_msg(format!("Subcommand 'node-ip' doesn't support arguments"))
	}
	},
	(_, None) => usage_msg(format!("Subcommands 'install/remove' require arguments")),
	match parse_args(env::args())? {
	(SubCommand::NodeIp, None) => node_ip()?,
	(SubCommand::NodeIp, Some(_) => usage_msg(format!("Subcommand 'node-ip' doesn't support arguments")).
	(subcommand, Some(args)) => match subcommand {
	SubCommand::Install => install(&args)?,
	SubCommand::Remove => remove(&args)?,
	},
	(_, None) => usage_msg(format!("Subcommands 'install/remove' require arguments")),

[bcressey]

(_, None) => usage_msg(format!("Subcommands 'install/remove' require arguments"))

For this it might be better to use the subcommand parameter so you can add it to the format string.

[webern]

I suggest:

enum Subcommand {
    Install(Args),
    Remove(Args),
    NodeIp,
}

And

fn parse_args(args: env::Args) -> Result<SubCommand> {
   // ...
}

[webern]

Actually since, since this would require us to stop using serde_plain to 'deserialize' the subcommand string, it's probably not worth it.

[zmrow]

@bcressey - The compiler wasn't smart enough to do your suggestion, it still wanted an exhaustive match of the enum variants inside the second match. I opted to split out the options a bit further and just avoid a nested match altogether.

[webern]

Is persisting the IP to a file an optimization (i.e. for faster queries)? Or is the persistence needed across reboots?

[webern]

Was this a cargo update?

[zmrow]

@webern Persisting the IP to file means that we can use it as the static IP for the setting kubernetes-node-ip, specifically for VMWare (since we don't have the luxury of IMDS).

[zmrow]

^ Addressed @bcressey 's comments and verified that /etc/resolv.conf and /proc/sys/kernel/hostname are both still set correctly.