network create: make --ipv6 optional

[akerouanton]

• relates to api: Make EnableIPv6 optional (impl #1 - pointer-based) moby/moby#47867

- What I did

The API field EnableIPv6 was marked as optional in our Swagger docs, and its default value in the Go client came from that field being a bool, thus defaulting to its zero value. That's not the case anymore.

This field is now a *bool as to let daemon's config define the default value. IPv6 can still be enabled / disabled by explicitly specifying the --ipv6 flag when doing docker network create.

- How to verify it

Start a daemon from moby/moby master branch:

$ ./build/docker-darwin-arm64 network create testnet
$ docker network inspect --format='{{ (index .IPAM.Config) }}' testnet
[{172.20.0.0/16  172.20.0.1 map[]}]

$ ./build/docker-darwin-arm64 network create --ipv6 testnetv6
$ docker network inspect --format='{{ (index .IPAM.Config) }}' testnetv6
[{172.19.0.0/16  172.19.0.1 map[]} {fdbc:8ec0:bb64::/64  fdbc:8ec0:bb64::1/64 map[]}]

Then restart the daemon with --default-network-opt=bridge=com.docker.network.enable_ipv6=true:

$ ./build/docker-darwin-arm64 network create testnetv6
$ docker network inspect --format='{{ (index .IPAM.Config) }}' testnetv6
[{172.20.0.0/16  172.20.0.1 map[]} {fd8c:5815:be1a::/64  fd8c:5815:be1a::1/64 map[]}]

$ ./build/docker-darwin-arm64 network create --ipv6=false testnet
$ docker network inspect --format='{{ (index .IPAM.Config) }}' testnet
[{172.19.0.0/16  172.19.0.1 map[]}]

- A picture of a cute animal (not mandatory but encouraged)

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 50.00000% with 2 lines in your changes missing coverage. Please review.

Project coverage is 61.34%. Comparing base (9b61bbb) to head (db2672e).

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #5126      +/-   ##
==========================================
- Coverage   61.37%   61.34%   -0.03%     
==========================================
  Files         298      295       -3     
  Lines       20717    20714       -3     
==========================================
- Hits        12715    12707       -8     
- Misses       7102     7104       +2     
- Partials      900      903       +3     

[thaJeztah]

LOL perhaps we need to create our own "optional bool" so that we could have nil as default. 🤔

Perhaps the flag-description should be updated though; something like "auto" (or "determined by daemon"?);

Suggested change

	flags.BoolVar(options.ipv6, "ipv6", false, "Enable IPv6 networking")
	flags.BoolVar(options.ipv6, "ipv6", false, "Enable or disable IPv6 networking (default is auto)")

or should we consider the default to be "true"?

Suggested change

	flags.BoolVar(options.ipv6, "ipv6", false, "Enable IPv6 networking")
	flags.BoolVar(options.ipv6, "ipv6", true, "Enable or disable IPv6 networking (default is enabled, if supported)")

[akerouanton]

or should we consider the default to be "true"?

I think we shouldn't do that, at least for now. One reason is the discussion we had regarding ip6tables. Another reason, IPv6 isn't supported by all drivers currently (eg. overlay).

If we want to enable IPv6 by default, I think it'd need to be done at the API level, in a new API version.

[thaJeztah]

Suggested change

	f := cmd.Flag("ipv6")
	if !f.Changed {
	if !cmd.Flag("ipv6").Changed {

or (not sure which one is more performant, but probably won't matter much)

Suggested change

	f := cmd.Flag("ipv6")
	if !f.Changed {
	if !cmd.Flags().Changed("ipv6") {

[thaJeztah]

Actually; would the reverse work? I see you have the var ipv6 bool added; that one could be set on the flag;

And this code could then do;

if cmd.Flag("ipv6").Changed {
	options.ipv6 = &ipv6
}

[akerouanton]

I chose cmd.Flag("ipv6").Changed instead of cmd.Flags().Changed("ipv6") as the former will trigger a panic if the flag is renamed / removed, whereas the latter will silently fail (ie. return false).

[thaJeztah]

LGTM

[thaJeztah]

The only thing I'm wondering is if we need to add more details about what the default is, but we can do in a follow-up.

[akerouanton]

@thaJeztah Sorry for the 1st version of this patch, it was crap. I should stop multi-tasking sometimes 😓

The only thing I'm wondering is if we need to add more details about what the default is, but we can do in a follow-up.

I think we need to update the documentation to explain how to set the default daemon-wide, how to disable ipv6 for a specific network, etc... but that's pretty much it. Do you have anything else in mind?

FWIW, we discussed docs updates a bit with @robmry and we decided to wait for at least the rc1 to start working on that -- we'd like to get every PR ready first.