Re: [MooseFS-Users] [v4] Suggestions about HA

[Gandalf C. <gan...@gm...>]

Il giorno mer 27 giu 2018 alle ore 11:11 Alexander AKHOBADZE
<ba...@ya...> ha scritto:
> I cant's see who prevents you to set up as many DNS servers as needed to
> achieve HA of DNS-service?
>
> They can be isolated from all the rest of network (i.e. by firewall) to
> be accessible only from MFS cluster parts.
>
> I.e. they also can colocate with Master servers on the same hardware and
> host some fake DNS zone which is used only by MFS cluster.

Let's assume an isolated network used as SAN.
In this network you don't have internet access (or you have it very
very limited)
Relying to an external DNS server is prone to DNS attacks (even
advanced DNS infrastructure
like Dyn.com and Amazon were down due to an attack last year)

If I have to add a local dns server only for MooseFS HA, I also need
to keep additional public dns server for
the rest of operating system (it doesn't matter if a public dns is
down for some hours on a SAN, in these hours i don't
run software updates or similiar, but the storage will be still up and running.

Adding an additional resolver to /etc/resolv.conf not connected to
anything, will slow down dns resolution, as all queries
against anything except the moosefs master domain will fail and a new
query (to another resolver should be made)

So, 3 solution:

1) an additional parameter in mfsmaster.cfg:
   MASTER_DNS_SERVER=127.0.0.1
to be used for HA. Then MooseFS will fetch master severs from that dns
server and not from the standard OS resolver.

2) adding a sort of scale-out dns service like Consul, so that each
master will register itself to Consul.

3) adding a local dns server with forwarning capabilty (in example,
PowerDNS). A local zone like "moosefs.master.lan" will be resolved
locally, everything else will be forwarded to a public dns server

Solution 2 is almost start-and-forget, solution 1 need some
adjustments every time a new master node is added (we have to set the
same value on
all local dns servers)

Solution 3 is similiar to solution 1, but doesn't require any extra
flag in MooseFS , because we can set the local resolver in
/etc/resolv.conf but still require
some adjustments every time we add/remove one master server (we have
to update the local zone file on every server)