[pve-devel] has somebody already tested corosync3 alpha et new knet transport ?

Thomas Lamprecht t.lamprecht at proxmox.com
Wed Jun 27 08:44:51 CEST 2018


On 6/27/18 8:35 AM, Alexandre DERUMIER wrote:
>>> FYI, knet is a abstraction layer, it still uses udp (aka multicast) 
> 
> Are you sure ? 
> 

I was but now not anymore, no ^^ Need to take a look at the code...

> 
> http://build.clusterlabs.org/corosync/presentations/2017-Kronosnet-The-new-face-of-corosync-communications.pdf 
> 
> Currently supported
> ○ UDP (unicast)
> ○ SCTP (connection-oriented)
> ○ Loopback (for localhost only … obviously)
> ○ No multicast, but could be added if really wanted
> ○ No broadcast
> ■ We are no longer that insane
> 
> 
> so udp unicast and sctp.
> 
> 
> and 
> 
> http://people.redhat.com/ccaulfie/docs/KnetCorosync.pdf
> 
> 
> Other options in the interface section do just what you might expect.
> mcastport: <n> 
>   tells knet to use that port number <n> for communication,. The default remains the old one of 5405
>   +linknumber, but you can override it per link here. Even though knet doesn't do actual multicasting
>   the name remains for old time's sake
> 
> 
> If it's really working without multicast, with lower latencies, that's a big improvement :)

yes would be :)

> 
>>> Are there links to the presentation, could be interesting :) 
> I'll try to get it. But it's was more about casual consistency vs paxos.
> The guy is only begining to implement his container orchestrator (in rust )
> 

Thanks!

> 
> 
> ----- Mail original -----
> De: "Thomas Lamprecht" <t.lamprecht at proxmox.com>
> À: "pve-devel" <pve-devel at pve.proxmox.com>, "aderumier" <aderumier at odiso.com>
> Envoyé: Mercredi 27 Juin 2018 08:02:30
> Objet: Re: [pve-devel] has somebody already tested corosync3 alpha et new knet transport ?
> 
> Hi, 
> 
> On 6/26/18 10:54 PM, Alexandre DERUMIER wrote: 
>> I have found this presentation about coming corosync3 (seem to be alpha recently) 
>> http://build.clusterlabs.org/corosync/presentations/2017-Kronosnet-The-new-face-of-corosync-communications.pdf 
>> with the new kronosnet (knet) transport. 
>>
> 
> Yes, tracking it somewhat since over half a year, looks really 
> good on paper but didn't not have yet time to do much testing - 
> as it'd be PVE 6.X timeframe anyway. 
> 
>>
>> Latencies results are really impressive and no more multicast ! (users will be happy ;) 
> 
> FYI, knet is a abstraction layer, it still uses udp (aka multicast) 
> As you do not get to handle a lot of links with a lot of nodes without 
> multicast - i.e., multicast is a very good thing, even if some hosting 
> environments and switch default settings are against it :) 
> It can also uses SCTP as transport method, which is a layer 4 protocol, 
> on the same level as UDP or TCP - i.e., it's not encapsulated in those. 
> 
>> and a lot of others improvments (dynamic mtu, ifdown/iup without breaking cluster, and seem to be compatible with corosync2 (with udp, udpu transports) 
>>
>> I'm still looking to make bigger proxmox clusters in the future :) 
> 
> Yes, looks definitly nice and it's on our radar, I'll try to build 
> a corosync 3 package if got a bit time to spare. 
> 
>> BTW, I was at a kubernetes/container conference at Paris today, 
>> and a talk of a guy was about trying to create in own orchestrator instead kubernetes (because of problem with etcd, network lag brigging down k8s master,...), 
>> talking about clusters, paxos, strong consistency. 
>>
>> He's looking to use a causal consistency model instead strong consistency, I never heard about this, 
>> but this seem really great to be able to manage bigger cluster, and also geo clusters. 
> 
> You can do more in parallel with it. In strong consistency models all 
> events (for our case, write/read operations) are ensured to be ordered. 
> If node A sees write OP-A happen before write OP-B then this principle 
> guarantee that all other nodes see OP-B after OP-A. 
> Casual consistency does this too, but only if OP-A and OP-B are related, 
> i.e., they affect each other (like a write to the same file would). 
> 
> Are there links to the presentation, could be interesting :) 
> Seems they use a a protocol named "cure" for the update replication: 
> https://pages.lip6.fr/Marc.Shapiro/papers/Cure-final-ICDCS16.pdf 
> 
>> He have given a link to an opensource key value store using causal consistency, called "antidote" 
>> https://syncfree.github.io/antidote/ 
>>
>> Maybe for the future (proxmox 10 ;), it could be great to have this kind of model. 
>> (I'm not enough expert to say if it could work, and If it could be possible to reimplement pmxcfs with this kind of protocol, and manage others things like pve-crm/lrm) 
> 
> Hmm, an academic erlang project with a bit short whitepaper, 
> I'm a bit wary on such projects - but sounds definitively interesting. 
> 
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