dhcp: Base for dhcp server

[jellonek]

• base skeleton for serving 2 protocols on 2 different connection types
• grpc on unix socket server for configuration providing/modifying/removal
• skeleton for dhcp server
• passing real data from configuration as options (ip/routes, hardcoded dns entries read from host?)

With this points fulfilled we will have possibility to add support for dhcp into calico branch.

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This change is

[jellonek]

https://github.com/Mirantis/virtlet/pull/110/files#diff-98e28311e3529c25828c931b46319afaR45 - this was chosen as a simple way to store/restore internal metadata. Also traversing through list is suboptimal, but for now - we don't need any extreme performance.

When this will be too slow - we will be able to change saving/updating/restoring metadata in hashmap, internally in simple map, externally - in e.x. redis or something similar.
This is not added now due to unnecessary complication and no need for greater performance for this moment.

[nhlfr]

Review status: 0 of 11 files reviewed at latest revision, 1 unresolved discussion.

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pkg/dhcp/README.md, line 5 at r1 (raw file):

```sh
  protoc --go_out=plugins=grpc:. configuration.proto

Why two spaces at the beginning?

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Comments from Reviewable

[jellonek]

Review status: 0 of 11 files reviewed at latest revision, 1 unresolved discussion.

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pkg/dhcp/README.md, line 5 at r1 (raw file):

Previously, nhlfr (Michal Rostecki) wrote…

Why two spaces at the beginning?

Good catch. Just habit. Will fix this.

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Comments from Reviewable

[jellonek]

For now, there is no passing any dns values - should be rethinked.

[ivan4th]

Review status: 0 of 12 files reviewed at latest revision, 3 unresolved discussions.

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cmd/dhcpserver/dhcp-server.go, line 45 at r2 (raw file):

      os.Exit(1)
  }
  glog.Infof("Starting server on socket %s", *socketPath)

glog.V(1) maybe?

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pkg/dhcp/server/dhcp_server.go, line 35 at r2 (raw file):

)

type dHCPServer struct {

somewhat strange casing, maybe dhcpServer ?

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Comments from Reviewable

[jellonek]

Review status: 0 of 12 files reviewed at latest revision, 3 unresolved discussions.

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cmd/dhcpserver/dhcp-server.go, line 45 at r2 (raw file):

Previously, ivan4th (Ivan Shvedunov) wrote…

glog.V(1) maybe?

Yes, good catch.

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pkg/dhcp/server/dhcp_server.go, line 35 at r2 (raw file):

Previously, ivan4th (Ivan Shvedunov) wrote…

somewhat strange casing, maybe dhcpServer ?

Specific shortcuts in golang should be named in upcase, like DNS, DHCP, IP, ID, but i tried to not export this from package and this is why it have so ugly name. I think that your proposal is much better.

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Comments from Reviewable

[ivan4th]

LGTM, but we need tests for that, and not just integration tests.

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Review status: 0 of 13 files reviewed at latest revision, 2 unresolved discussions.

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Comments from Reviewable

[ivan4th]

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Review status: 0 of 13 files reviewed at latest revision, 2 unresolved discussions.

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Comments from Reviewable