Re: Numen with reference to vmap

["Serguei Bezverkhi (sbezverk)" <sbezverk@cisco.com>]

Hi Phil,

I can also minimize any impact by inserting a new rule in front of the old one, and then delete the old one. So in this case there should no any impact. Here is iptables rules I try to mimic:

// -A KUBE-SVC-57XVOCFNTLTR3Q27 -m statistic --mode random --probability 0.50000000000 -j KUBE-SEP-FS3FUULGZPVD4VYB
// -A KUBE-SVC-57XVOCFNTLTR3Q27 -j KUBE-SEP-MMFZROQSLQ3DKOQA
// !
// ! Endpoint 1 for KUBE-SVC-57XVOCFNTLTR3Q27
// !
// -A KUBE-SEP-FS3FUULGZPVD4VYB -s 57.112.0.247/32 -j KUBE-MARK-MASQ
// -A KUBE-SEP-FS3FUULGZPVD4VYB -p tcp -m tcp -j DNAT --to-destination 57.112.0.247:8080
// !
// ! Endpoint 2 for KUBE-SVC-57XVOCFNTLTR3Q27
// !
// -A KUBE-SEP-MMFZROQSLQ3DKOQA -s 57.112.0.248/32 -j KUBE-MARK-MASQ
// -A KUBE-SEP-MMFZROQSLQ3DKOQA -p tcp -m tcp -j DNAT --to-destination 57.112.0.248:8080

As you can see SVC chain KUBE-SVC-57XVOCFNTLTR3Q27 load balance between 2 endpoints.

Thank you
Serguei


On 2019-12-04, 10:19 AM, "n0-1@orbyte.nwl.cc on behalf of Phil Sutter" <n0-1@orbyte.nwl.cc on behalf of phil@nwl.cc> wrote:

    Hi,
    
    On Wed, Dec 04, 2019 at 01:47:47PM +0000, Serguei Bezverkhi (sbezverk) wrote:
    > Thank you for your reply. It is very unfortunate indeed. Here is the scenario where I thought to use a non-anonymous vmap.
    > 
    > Each k8s service can have 0, 1 or more associated endpoints, backends (pods providing this service). 0 endpoint already taken care of in filter prerouting hook.  When there are 1 or more, proxy needs to load balance incoming connections between endpoints.I thought to create vmap per service with 1 rule per service . When an endpoint gets updated (add/deleted) which could happen anytime then the only vmap get corresponding update and my hope was that automagically load balancing will be adjusted to use updated endpoints list.
    > 
    > With what you explained, I am not sure if dynamic load balancing is possible at all. If numgen work only with static anonymous vmap and fixed modulus , the only way to address this dynamic nature of endpoints is to recreate service rule everytime when number of endpoints changes (recalculate modulus and entries in vmap). I suspect it is way less efficient.
    
    Well, if you have a modulus of, say, 5 and your vmap contains only
    entries 0 to 3 your setup is broken anyway. So I guess you will need to
    adjust modulus along with entries in vmap at all times.
    
    What is the iptables-equivalent you want to replace? Maybe that serves
    as inspiration for how to solve it in nftables.
    
    > What will happen to dataplane and packets in transit when the rule will be deleted and then recreated? I suspect it might result in dropped packets, could you please comment on the possible impact?
    
    Well, you could replace the rule in a single transaction, that would
    eliminate the timespan the rule doesn't exist. AFAICT, this is RCU-based
    so packets will either hit the old or the new rule then.
    
    Cheers, Phil