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Posted to dev@tomcat.apache.org by Stephen Wick <sw...@NicholsonKovac.com> on 2007/11/02 22:04:42 UTC
Are Sticky Sessions really necessary?
The Tomcat 5.5 "Clustering/Session Replication Guide" says, "Make sure
that your loadbalancer is configured for sticky session mode." However,
I don't see the term "Sticky" sessions anywhere in the Servlet 2.3 or
2.4 specifications.
Are sticky sessions really required for clustering to function properly
in Tomcat 5.5? I thought that session replication would eliminate any
need to direct a client session to one node in a cluster.
If not, can we adjust the documentation to indicate that Sticky sessions
are optional, for the appropriate reason (I'm guessing the advent of
session replication in tomcat.)
I am asking this question because I am having trouble with Sticky
sessions in my load balancer, and I need to know whether or not I should
pursue fixing this feature. If tomcat doesn't really require sticky
sessions, then I can leave my load balancer alone. If tomcat does need
the feature to function properly, then I need to go to some additional
expense to resolve the issue with my load balancing appliance.
Thank you for your time and expertise.
Stephen Wick
Interactive Developer
Nicholson Kovac, Inc.
References
http://tomcat.apache.org/tomcat-5.5-doc/cluster-howto.html
Re: Are Sticky Sessions really necessary?
Posted by "Preston L. Bannister" <pr...@bannister.us>.
On 11/3/07, Len Popp <le...@gmail.com> wrote:
>
> But isn't the purpose of session replication to allow different
> servers to handle the session? If not, what's it for?
>
This discussion touches on a bit of philosophy, and a set of design
decisions built into the code, and no longer relevant. In this case it's
"sticky sessions", a notion that once made some sense, but no longer. There
are really only two design points that make sense for sessions: 1) sessions
kept in-memory (or on-disk) within a single machine, and 2) sessions kept in
an external service (database or specialized store). There are a bunch of
intermediate solutions that used to make some sense - before web-oriented
databases, before massive scaling, before gigabit local nets, before cheap
and insanely fast single-box systems.
All the time spent maintaining intermediate solutions removes focus. Java
is not losing out to PHP (and the like) due to lack of focus on the present,
not inferior technology.
Not that I expect the argument to make any headway in this venue, but
someone has to raise the issue.
Re: Are Sticky Sessions really necessary?
Posted by Peter Rossbach <pr...@objektpark.de>.
Hi Len,
the normal servlet spec conform purpose is to handle administration
down, app version migration or
handle real crashes without lost your user session/context! This
means not that tomcat replication cluster can't handle your "request
stateless" szenario. It works
with speziell application, but to build those application is a very
hard job. You can test it with pooled replication mode, but it's high
risk to have inconsistence at normal runtime. You must have good
synchronization points to handle multiple request at same session at
lots of threads and processes. Please, check how your browser client
interact exactly with your application. At my experience the sticky
session constraint help to have a better and controlled server env :-)
Peter
Am 03.11.2007 um 16:16 schrieb Len Popp:
> But isn't the purpose of session replication to allow different
> servers to handle the session? If not, what's it for?
> --
> Len
>
> On 11/3/07, Peter Rossbach <pr...@objektpark.de> wrote:
>> Hi,
>>
>> It is not only ineffizient and a risk, Read 7.7.2 at the spec:
>>
>> SRV.7.7.2 Distributed Environments
>> Within an application marked as distributable, all requests that are
>> part of a session
>> must be handled by one Java Virtual Machine1 ("JVM") at a time. The
>> container
>> must be able to handle all objects placed into instances of the
>> HttpSession class
>> using the setAttribute or putValue methods appropriately.
>> ....
>>
>> regards
>> Peter
>>
>> Am 02.11.2007 um 22:37 schrieb Len Popp:
>>
>>> You can indeed use session replication without sticky sessions, and
>>> the session data will be copied to all the Tomcat servers.
>>> However it
>>> may be inefficient. You probably have to use synchronous replication
>>> to ensure the session data is consistent across the cluster, which
>>> adds latency to the requests. And there could be a lot of extra
>>> network traffic in the cluster if it's busy (which it is, otherwise
>>> you wouldn't be doing load balancing).
>>>
>>> (I haven't used session replication in a high-load situation. Maybe
>>> someone else can tell us how well it works.)
>>> --
>>> Len
>>>
>>> On 11/2/07, Stephen Wick <sw...@nicholsonkovac.com> wrote:
>>>> The Tomcat 5.5 "Clustering/Session Replication Guide" says, "Make
>>>> sure
>>>> that your loadbalancer is configured for sticky session mode."
>>>> However,
>>>> I don't see the term "Sticky" sessions anywhere in the Servlet
>>>> 2.3 or
>>>> 2.4 specifications.
>>>>
>>>> Are sticky sessions really required for clustering to function
>>>> properly
>>>> in Tomcat 5.5? I thought that session replication would eliminate
>>>> any
>>>> need to direct a client session to one node in a cluster.
>>>>
>>>> If not, can we adjust the documentation to indicate that Sticky
>>>> sessions
>>>> are optional, for the appropriate reason (I'm guessing the
>>>> advent of
>>>> session replication in tomcat.)
>>>>
>>>> I am asking this question because I am having trouble with Sticky
>>>> sessions in my load balancer, and I need to know whether or not I
>>>> should
>>>> pursue fixing this feature. If tomcat doesn't really require
>>>> sticky
>>>> sessions, then I can leave my load balancer alone. If tomcat does
>>>> need
>>>> the feature to function properly, then I need to go to some
>>>> additional
>>>> expense to resolve the issue with my load balancing appliance.
>>>>
>>>> Thank you for your time and expertise.
>>>>
>>>> Stephen Wick
>>>> Interactive Developer
>>>> Nicholson Kovac, Inc.
>>>>
>>>> References
>>>> http://tomcat.apache.org/tomcat-5.5-doc/cluster-howto.html
>>>>
>>>
>>> --------------------------------------------------------------------
>>> -
>>> To unsubscribe, e-mail: dev-unsubscribe@tomcat.apache.org
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>>>
>>>
>>
>>
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>>
>>
>
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Re: Are Sticky Sessions really necessary?
Posted by Len Popp <le...@gmail.com>.
But isn't the purpose of session replication to allow different
servers to handle the session? If not, what's it for?
--
Len
On 11/3/07, Peter Rossbach <pr...@objektpark.de> wrote:
> Hi,
>
> It is not only ineffizient and a risk, Read 7.7.2 at the spec:
>
> SRV.7.7.2 Distributed Environments
> Within an application marked as distributable, all requests that are
> part of a session
> must be handled by one Java Virtual Machine1 ("JVM") at a time. The
> container
> must be able to handle all objects placed into instances of the
> HttpSession class
> using the setAttribute or putValue methods appropriately.
> ....
>
> regards
> Peter
>
> Am 02.11.2007 um 22:37 schrieb Len Popp:
>
> > You can indeed use session replication without sticky sessions, and
> > the session data will be copied to all the Tomcat servers. However it
> > may be inefficient. You probably have to use synchronous replication
> > to ensure the session data is consistent across the cluster, which
> > adds latency to the requests. And there could be a lot of extra
> > network traffic in the cluster if it's busy (which it is, otherwise
> > you wouldn't be doing load balancing).
> >
> > (I haven't used session replication in a high-load situation. Maybe
> > someone else can tell us how well it works.)
> > --
> > Len
> >
> > On 11/2/07, Stephen Wick <sw...@nicholsonkovac.com> wrote:
> >> The Tomcat 5.5 "Clustering/Session Replication Guide" says, "Make
> >> sure
> >> that your loadbalancer is configured for sticky session mode."
> >> However,
> >> I don't see the term "Sticky" sessions anywhere in the Servlet 2.3 or
> >> 2.4 specifications.
> >>
> >> Are sticky sessions really required for clustering to function
> >> properly
> >> in Tomcat 5.5? I thought that session replication would eliminate
> >> any
> >> need to direct a client session to one node in a cluster.
> >>
> >> If not, can we adjust the documentation to indicate that Sticky
> >> sessions
> >> are optional, for the appropriate reason (I'm guessing the advent of
> >> session replication in tomcat.)
> >>
> >> I am asking this question because I am having trouble with Sticky
> >> sessions in my load balancer, and I need to know whether or not I
> >> should
> >> pursue fixing this feature. If tomcat doesn't really require sticky
> >> sessions, then I can leave my load balancer alone. If tomcat does
> >> need
> >> the feature to function properly, then I need to go to some
> >> additional
> >> expense to resolve the issue with my load balancing appliance.
> >>
> >> Thank you for your time and expertise.
> >>
> >> Stephen Wick
> >> Interactive Developer
> >> Nicholson Kovac, Inc.
> >>
> >> References
> >> http://tomcat.apache.org/tomcat-5.5-doc/cluster-howto.html
> >>
> >
> > ---------------------------------------------------------------------
> > To unsubscribe, e-mail: dev-unsubscribe@tomcat.apache.org
> > For additional commands, e-mail: dev-help@tomcat.apache.org
> >
> >
>
>
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>
>
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Re: Are Sticky Sessions really necessary?
Posted by Peter Rossbach <pr...@objektpark.de>.
Hi,
It is not only ineffizient and a risk, Read 7.7.2 at the spec:
SRV.7.7.2 Distributed Environments
Within an application marked as distributable, all requests that are
part of a session
must be handled by one Java Virtual Machine1 (“JVM”) at a time. The
container
must be able to handle all objects placed into instances of the
HttpSession class
using the setAttribute or putValue methods appropriately.
....
regards
Peter
Am 02.11.2007 um 22:37 schrieb Len Popp:
> You can indeed use session replication without sticky sessions, and
> the session data will be copied to all the Tomcat servers. However it
> may be inefficient. You probably have to use synchronous replication
> to ensure the session data is consistent across the cluster, which
> adds latency to the requests. And there could be a lot of extra
> network traffic in the cluster if it's busy (which it is, otherwise
> you wouldn't be doing load balancing).
>
> (I haven't used session replication in a high-load situation. Maybe
> someone else can tell us how well it works.)
> --
> Len
>
> On 11/2/07, Stephen Wick <sw...@nicholsonkovac.com> wrote:
>> The Tomcat 5.5 "Clustering/Session Replication Guide" says, "Make
>> sure
>> that your loadbalancer is configured for sticky session mode."
>> However,
>> I don't see the term "Sticky" sessions anywhere in the Servlet 2.3 or
>> 2.4 specifications.
>>
>> Are sticky sessions really required for clustering to function
>> properly
>> in Tomcat 5.5? I thought that session replication would eliminate
>> any
>> need to direct a client session to one node in a cluster.
>>
>> If not, can we adjust the documentation to indicate that Sticky
>> sessions
>> are optional, for the appropriate reason (I'm guessing the advent of
>> session replication in tomcat.)
>>
>> I am asking this question because I am having trouble with Sticky
>> sessions in my load balancer, and I need to know whether or not I
>> should
>> pursue fixing this feature. If tomcat doesn't really require sticky
>> sessions, then I can leave my load balancer alone. If tomcat does
>> need
>> the feature to function properly, then I need to go to some
>> additional
>> expense to resolve the issue with my load balancing appliance.
>>
>> Thank you for your time and expertise.
>>
>> Stephen Wick
>> Interactive Developer
>> Nicholson Kovac, Inc.
>>
>> References
>> http://tomcat.apache.org/tomcat-5.5-doc/cluster-howto.html
>>
>
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> To unsubscribe, e-mail: dev-unsubscribe@tomcat.apache.org
> For additional commands, e-mail: dev-help@tomcat.apache.org
>
>
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Re: Are Sticky Sessions really necessary?
Posted by Len Popp <le...@gmail.com>.
You can indeed use session replication without sticky sessions, and
the session data will be copied to all the Tomcat servers. However it
may be inefficient. You probably have to use synchronous replication
to ensure the session data is consistent across the cluster, which
adds latency to the requests. And there could be a lot of extra
network traffic in the cluster if it's busy (which it is, otherwise
you wouldn't be doing load balancing).
(I haven't used session replication in a high-load situation. Maybe
someone else can tell us how well it works.)
--
Len
On 11/2/07, Stephen Wick <sw...@nicholsonkovac.com> wrote:
> The Tomcat 5.5 "Clustering/Session Replication Guide" says, "Make sure
> that your loadbalancer is configured for sticky session mode." However,
> I don't see the term "Sticky" sessions anywhere in the Servlet 2.3 or
> 2.4 specifications.
>
> Are sticky sessions really required for clustering to function properly
> in Tomcat 5.5? I thought that session replication would eliminate any
> need to direct a client session to one node in a cluster.
>
> If not, can we adjust the documentation to indicate that Sticky sessions
> are optional, for the appropriate reason (I'm guessing the advent of
> session replication in tomcat.)
>
> I am asking this question because I am having trouble with Sticky
> sessions in my load balancer, and I need to know whether or not I should
> pursue fixing this feature. If tomcat doesn't really require sticky
> sessions, then I can leave my load balancer alone. If tomcat does need
> the feature to function properly, then I need to go to some additional
> expense to resolve the issue with my load balancing appliance.
>
> Thank you for your time and expertise.
>
> Stephen Wick
> Interactive Developer
> Nicholson Kovac, Inc.
>
> References
> http://tomcat.apache.org/tomcat-5.5-doc/cluster-howto.html
>
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