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[CC Pablo]
Hi Alex,
On Wed, Aug 26, 2015 at 10:47:52AM -0700, Alex Gartrell wrote:
> The configuration of ipvs at Facebook is relatively straightforward. All
> ipvs instances bgp advertise a set of VIPs and the network prefers the
> nearest one or uses ECMP in the event of a tie. For the uninitiated, ECMP
> deterministically and statelessly load balances by hashing the packet
> (usually a 5-tuple of protocol, saddr, daddr, sport, and dport) and using
> that number as an index (basic hash table type logic).
>
> The problem is that ICMP packets (which contain really important
> information like whether or not an MTU has been exceeded) will get a
> different hash value and may end up at a different ipvs instance. With no
> information about where to route these packets, they are dropped, creating
> ICMP black holes and breaking Path MTU discovery. Suddenly, my mom's
> pictures can't load and I'm fielding midday calls that I want nothing to do
> with.
>
> To address this, this patch set introduces the ability to schedule icmp
> packets which is gated by a sysctl net.ipv4.vs.schedule_icmp. If set to 0,
> the old behavior is maintained -- otherwise ICMP packets are scheduled.
Nice work.
I have queued these up with Julian's Ack in the ipvs-next tree.
At this stage my plan is to send a pull request to Pablo targeted
at v4.4 after v4.3-rc1 has been released. I will probably rebase ipvs-next
at that time.
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