Something like the following:
HAProxy1 --------> Tomcat1
| +++++++++/\
| +
|--------+--->Tomcat2
+ /+\
+ +
HAProxy2+++++++
HAProxy1 is in the same machine as Tomcat1
HAproxy2 is in the same machine as Tomcat2
HAProxy1 distributes the load among Tomcat1 and Tomcat2.
I erroneously thought that HAProxy2 would take over when HAProxy1 crashed to
distribute the load among Tomcat1/Tomcat2.
So if both are independent what can I do?
________________________________
From: David Coulson <da...@davidcoulson.net>
To: Hermes Flying <flyingher...@yahoo.com>
Cc: Baptiste <bed...@gmail.com>; "haproxy@formilux.org" <haproxy@formilux.org>
Sent: Thursday, November 29, 2012 9:12 PM
Subject: Re: HAproxy and detect split-brain (network failures)
Again, you are mixing everything up.
HAProxy has it's own configuration - It defines what nodes your port
80 traffic (or whatever) is routed to. Haproxy does periodic health
checks of these backend services to make sure they are available for
requests. If you have multiple haproxy instances they will all
independently do health checks and not share any of that information
with each other. HAProxy will route traffic to all systems defined
as a backend for a particular service based upon whatever criteria
is in the haproxy config.
You can run a two-node environment that is active/backup from a VIP
perspective, but active/active from a haproxy service perspective -
Each node would run Apache (or whatever your service is) and haproxy
would distribute requests across both based on your haproxy config.
But, at any point in time only one node would actually be routing
requests through it's local instance of haproxy.
I can't make it any simpler than that. Draw a diagram of what you
are trying to do if it doesn't make sense.
On 11/29/12 2:06 PM, Hermes Flying wrote:
You are saying that one instance of HAProxy runs in each system and one
instance is assigned the VIP that clients hit-on (out of scope for HAProxy).
>But this HAProxy distributes the requests according to the load, either on
>system-A or system-B for which you seem to refer to as backup system. In what
>way are you now refering to it as backup system? Because I am interested in
>distributing the load to all the nodes.
>
>
>
>From: David Coulson mailto:da...@davidcoulson.net
>To: Hermes Flying mailto:flyingher...@yahoo.com
>Cc: Baptiste mailto:bed...@gmail.com; mailto:haproxy@formilux.org
>mailto:haproxy@formilux.org
>Sent: Thursday, November 29, 2012 8:57 PM
>Subject: Re: HAproxy and detect split-brain (network failures)
>
>
>You can do that, but haproxy doesn't have anything to do with the failover
>process, other than you run an instance of haproxy on one server, and another
>instance on your backup system. As I said, neither of the haproxy instances
>communicate anything, so all you need to do is move the IP clients are using
>from one server to the other in order to handle a failure. Moving the IP
>around is something keepalived, pacemaker, etc handles - Look at their
>documentation for specifics and challenges in a two-node config.
>
>HAProxy doesn't have a concent of primary and backup
in terms of it's own instances. Each of them is stand
alone. It's up to you, based on your network/IP config
which one has traffic routed to it.
>
>David
>
>
>
>On 11/29/12 1:53 PM, Hermes Flying wrote:
>
>But if I install 2 HAProxy as load balancers, doesn't one act as the primary
>loadbalancer directing the load to the known servers while the secondary takes
>over load distribution as soon as the heartbeat fails? I remember reading
>this. Is this wrong?
>>
>>
>>From: David Coulson mailto:da...@davidcoulson.net
>>To: Hermes Flying mailto:flyingher...@yahoo.com
>>Cc: Baptiste mailto:bed...@gmail.com; mailto:haproxy@formilux.org
>>mailto:haproxy@formilux.org
>>Sent: Thursday, November 29, 2012 8:39 PM
>>Subject: Re: HAproxy and detect split-brain (network failures)
>>
>>
>>You are mixing two totally different things together.
>>
>>1) HAProxy will do periodic health checks
of backend systems you are routing to.
Depending if you configure something as
'backup' or 'not backup' will determine
if/how traffic is routed to it. The
backend systems do not 'take over'.
Haproxy just routes traffic to systems
based on your configuration. The backend
systems don't know/care about the other
backend nodes, unless your application
requires it which is a different story and
nothing to do with haproxy. HAproxy only
cares about a single instance of itself -
If you have more than one haproxy
instance, they do NOT communicate anything
between each other.
>>
>>2) In terms of keepalived, pacemaker, etc,
it makes no difference which you use with
haproxy - all they do is manage the IP
address(es) which haproxy is listening on,
and perhaps restart haproxy if it dies.
Their configuration and how you maintain
quorum in a two-node configuration is a
question for one of their mailing lists,
or just read their documentation. I
personally use pacemaker.
>>
>>
>>On 11/29/12 1:35 PM, Hermes Flying wrote:
>>
>>Well I don't follow:
>>>"You can have a pool of primary that it routes across, then backup systems
>>>that are only used when all primary systems are unavailable."
>>>When you are saying that "the backup systems that are used when primary
>>>systems are unavailable", how do they decide to take over? How do they know
>>>that the other systems are unavailable?
>>>Are you saying that they depend on third party components like the ones you
>>>mentioned (Keepalived etc)? In this case, what is the most suitable tool to
>>>be used along with HAProxy? Is there a reference manual for this somewhere?
>>>
>>>
>>>
>>>From: David Coulson mailto:da...@davidcoulson.net
>>>To: Hermes Flying mailto:flyingher...@yahoo.com
>>>Cc: Baptiste mailto:bed...@gmail.com; mailto:haproxy@formilux.org
>>>mailto:haproxy@formilux.org
>>>Sent: Thursday, November 29, 2012 8:21 PM
>>>Subject: Re: HAproxy and detect split-brain (network failures)
>>>
>>>
>>>HAProxy only does primary and backup in terms of active backend systems -
>>>You can have a pool of primary that it routes across, then backup systems
>>>that are only used when all primary systems are unavailable.
>>>
>>>There is no concept of a
cluster in terms of haproxy
instances, although you can
run more than one and manage
them via something like
pacemaker, keepalived or
rgmanager.
>>>
>>>
>>>On 11/29/12 1:19 PM, Hermes Flying wrote:
>>>
>>>Hi,
>>>>From a quick look into HAProxy, I see that it is a Primary/backup
>>>>architecture. So isn't ensuring that both "nodes" don't become primary part
>>>>of HAProxy's primary/backup "protocol" ?
>>>>
>>>>
>>>>From: Baptiste mailto:bed...@gmail.com
>>>>To: Hermes Flying mailto:flyingher...@yahoo.com
>>>>Cc: mailto:haproxy@formilux.org mailto:haproxy@formilux.org
>>>>Sent: Thursday, November 29, 2012 3:02 PM
>>>>Subject: Re: HAproxy and detect split-brain (network failures)
>>>>
>>>>Hi,
>>>>
>>>>This is not
HAProxy's role, this
is the tool you use
to ensure high
>>>>availability to do
that.
>>>>
>>>>I could see a way
where HAProxy can
report one interface
failing,
>>>>maybe this could
help you to detect
if you're in a split
brain
>>>>situation.
>>>>
>>>>cheers
>>>>
>>>>
>>>>
>>>>On Thu, Nov 29, 2012
at 11:51 AM, Hermes
Flying
<flyingher...@yahoo.com> wrote:
>>>>> Hi,
>>>>> I am looking
into using HAProxy
as our load
balancer.
>>>>> I see that you
are using a
primary/backup
approach. I was
wondering how does
>>>>> HAProxy (if it
does) address
split-brain
situation? Do you
have a mechanism
>>>>> to detect and
avoid it? Do you
have some standard
recommendation to
all
>>>>> those using
your solution?
>>>>>
>>>>> Thanks
>>>>
>>>>
>>>>
>>>
>>>
>>>
>>
>>
>>
>
>
>
