Replace ISC dhcp4-server with isc-kea-dhcp4-server

[1977er]

My very first PR.

[AiyionPrime]

I just looked into it;
with kea it should finally be easy enough to omit the dhcp leases in logs at all.

in the configuration docs is a topic about how to assign log levels to log topics like this:

"loggers": [{
            "name": "*",
            "severity": "DEBUG"
        }]

The loggers are then listed in the logger section.
The ones we care for are kea-dhcp4.leases and possibly kea-dhcp6.leases.

Their severity can be set to log-level NONE as stated here.

I'd really like to see us making use of this great feature as it would get rid of #70, finally.

Please let me know what you think about this opportunity.

[1977er]

The current proposed config logs events with a severity of WARN and above. Afaik lease information are already left out. I will keep an eye on it while deploying the first (test) installations.

I would not recommend turning off logging at all (loglevel NONE).

[1977er]

Tested on sn01. Seems to work fine.

[lemoer]

Does this mean, it has been rolled out on all supernodes?

[1977er]

Nope. Only on sn01 so far. Let's test it for some days before we break all our supernodes.

[1977er]

On the hardly used sn01 we get a handful of "kea-dhcp4[XXX]: ERROR [kea-dhcp4.packets.140175791149824] DHCP4_BUFFER_RECEIVE_FAIL error on attempt to receive packet: Truncated DHCPv4 packet (len=0) received, at least 236 is expected." messages per day. We might want to silence them with mailfilters in the journald role.

[AiyionPrime]

Please keep in mind, that I role out master on our supernodes on a regular basis.
I always assume master is tested and safe to deploy.

It's not really an option to keep in mind which tags are safe to deploy and which aren't.

[CodeFetch]

@AiyionPrime I actually thought that we should roll out the change on all supernodes. I think that rolling the change out on a single supernode does not really help in finding issues... That's something we could have done if we'd have a parallel test network as 1977er suggested.

@1977er To me it looks quite stable. At least as stable as ISC. So shall we roll it out everywhere or shall we modify the Playbooks and restore the old dhcp-role as "legacy_dhcp" or something and use it for the supernodes running ISC DHCP?

[1977er]

When rolling out KEA: deinstallation of legacy isc-dhcpd was not in the scope of this role and has to be done manually.
Should be done by night when fewer endusers are affected.

[AiyionPrime]

isc-dhcp-server is the one to be removed,
isc-dhcp-common contains manpages for both server and client and is irrelevant;
what ever isc-dhcp-client does in our system, I left it where it was on both sn07 and sn09.

[1977er]

I assumed isc-dhcp-client ships dhclient which is partially used on some systems to get ip addresses for eth0 from ISPs. There I did not touch that one.

[1977er]

This PR is already merged and targets a removed package now. Can we close and remove it?

[AiyionPrime]

I did not intend to reopen it, just thought this would be a good place to discuss the manual migration strategy.