Open Stack

On Sep 20, 2016, at 10:06 PM, Alexandr Porunov wrote:

> If you care about high availability (as I do) then you need to have
> additional keystone instance which will prevent your cluster from SPOF.

That was the idea. One node is already dedicated for that, but I haven't
installed it yet, because I'm not sure what the right way to do this is.

I've been reading the high availability docs for the last couple of weeks
now, but they don't talk about the most basic things :(. For once, they
get right down to it (which I've complained about other docs don't in the
past :D).


IF (!) I understand things correctly, services report themselves into
the catalog (which is basically the *SQL server). This catalog is Keystone.

So my first Keystone server have registered itself as:

bladeA01:~# openstack endpoint list | grep keystone
| 26855d6e55284651a0fcaa5cf25b3d90 | europe-london | keystone     | identity            | True    | internal  | http://10.0.4.1:5000/v2.0                  |
| 72eb76cdb6cf4db3813eac4a683e4e34 | europe-london | keystone     | identity            | True    | public    | http://10.0.4.1:5000/v2.0                  |
| c95ce66a4efa46b4855185d088279824 | europe-london | keystone     | identity            | True    | admin     | http://10.0.4.1:35357/v2.0                 |

Now, I'm assuming that the second one will do the same (on ITS IP of
course). So "anyone" needing to contact Keystone, will, I assume,
consult this catalog and "pick one".


So if I use a DNS round-robin for the two keystones:

    openstack.domain.tld.    1 IN A 10.0.4.1
    openstack.domain.tld.    1 IN A 10.0.4.9

the entry for 'openstack.domain.tld.' will be invalidated every second,
practically making sure that a new request will be given every time.
The downside is that if the .1 keystone is down, the service will have
to wait for the time out before it can ask the next one.

Round-robin is "poor mans load balancer", and it have many flaws, but
it will at least give some form of using all available resources at any
one time.

> For it I use the same virtual IP address for both keystone instances
> managed by keepalived.

That is more like a hot-standby (only one server is used at any one time)
and I guess that's an option as well. But because I have limited resources,
I'd prefer, if possible, to use all of them all the time.

Balancing the load is less of an issue than high availability is, but
if possible, I'd like to solve both of them :).

> Also you can use peacemaker and other stuff to reach high availability

Yes, but I'm guessing those need _another_ machine in front of the ones
I want to load balance. And if that goes down, EVERYTHING stops working.
Unless they are clustered, which require _even more_ machines!

Which I don't have. I don't want to dedicate a dual CPU, eight core
Intel Xeon E5530 @ 2.40GHz just to swap traffic around! It's a huge
waste of precious resources. And if I add smaller machines outside of
the blade center, then ALL traffic needs to go out in the rack and then
back in, which will affect performance (which is already kind'a bad
because it's an older setup with only Gbps links).

I had to dedicate one whole switch (there's two Cisco 3020 in the
blade center) just for the truncated link down to the storage. Which
is another think I need to solve eventually - it is currently the biggest,
badest SPOF :( :(.
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