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Posted to users@tomcat.apache.org by "Li,Henry" <he...@mdanderson.org> on 2009/07/30 17:35:24 UTC
How to configure failover for Apache/Tomcat?
I need help--- I have two Apache web servers, two app servers with four Tomcat instances running on them (two Tomcat instances on each server). All four servers run on Red Hat Linux. Current configuration is: web1 connected to app1 only, web2 connected to app2 only. If app1 is down, all users connected to web1 are out. Is it possible to configure web1 connecting to both app1 and app2 so failover will be available? What extra hardware and/or software do I need?
Thanks,
Henry
RE: How to configure failover for Apache/Tomcat?
Posted by "Li,Henry" <he...@mdanderson.org>.
Thank you Chris! I did not use mod_jk before. I will start from the beginning.
Henry
-----Original Message-----
From: Christopher Schultz [mailto:chris@christopherschultz.net]
Sent: Thursday, July 30, 2009 11:03 AM
To: Tomcat Users List
Subject: Re: How to configure failover for Apache/Tomcat?
-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA1
Henry,
On 7/30/2009 11:35 AM, Li,Henry wrote:
> I have two Apache web servers, two app servers with
> four Tomcat instances running on them (two Tomcat instances on each
> server). All four servers run on Red Hat Linux. Current configuration
> is: web1 connected to app1 only, web2 connected to app2 only.
So:
web1 ---> app1 [ Tomcat 1a, Tomcat 1b]
web2 ---> app2 [ Tomcat 1a, Tomcat 2b]
Right?
> If
> app1 is down, all users connected to web1 are out. Is it possible to
> configure web1 connecting to both app1 and app2 so failover will be
> available?
Yes. Given your existing configuration, it seems that using mod_jk to
connect your Apache httpd instances to Tomcat is the right way to go:
mod_jk supports clustering and load balancing in (roughly) the following
way:
1. Create a worker for each back-end Tomcat instance you have
2. Collect all the workers above into a "balancer" worker that will
really multiplex between the workers defined in step 1
3. Session-less users are routed to whichever back-end server makes
sense based upon your chosen load balancing algorithm
4. Users /with/ sessions are always router to the server that "owns"
their session
5. When a server fails, mod_jk detect this and forwards requests to
one of the other members of the cluster
6. When the failed node comes back up, it re-joins the cluster and
everything goes back to normal
Note that you can either implement sticky sessions (as I have described
above), or you can use session replication across your cluster. I'm not
a big fan of session replication because of all the messages that need
to be sent around. For my production purposes, requiring a user to login
again when failover occurs is acceptable. For me, the complexity of
session replication is not necessary. Your requirements may differ.
For more information on mod_jk balancing and clustering, see this page:
http://tomcat.apache.org/connectors-doc/generic_howto/loadbalancers.html
This page presupposes an understanding of how mod_jk is configured. If
you haven't used mod_jk before, start here:
http://tomcat.apache.org/connectors-doc/
and read the links for "All about workers", "For the impatient", and the
reference guide for Apache. If you have more questions, post back to the
list.
> What extra hardware and/or software do I need?
You'll want a hardware load-balancer to balance between web1 and web2.
As for software, just adding mod_jk to the mix should do it.
- -chris
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Re: How to configure failover for Apache/Tomcat?
Posted by Christopher Schultz <ch...@christopherschultz.net>.
-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA1
Henry,
On 7/30/2009 11:35 AM, Li,Henry wrote:
> I have two Apache web servers, two app servers with
> four Tomcat instances running on them (two Tomcat instances on each
> server). All four servers run on Red Hat Linux. Current configuration
> is: web1 connected to app1 only, web2 connected to app2 only.
So:
web1 ---> app1 [ Tomcat 1a, Tomcat 1b]
web2 ---> app2 [ Tomcat 1a, Tomcat 2b]
Right?
> If
> app1 is down, all users connected to web1 are out. Is it possible to
> configure web1 connecting to both app1 and app2 so failover will be
> available?
Yes. Given your existing configuration, it seems that using mod_jk to
connect your Apache httpd instances to Tomcat is the right way to go:
mod_jk supports clustering and load balancing in (roughly) the following
way:
1. Create a worker for each back-end Tomcat instance you have
2. Collect all the workers above into a "balancer" worker that will
really multiplex between the workers defined in step 1
3. Session-less users are routed to whichever back-end server makes
sense based upon your chosen load balancing algorithm
4. Users /with/ sessions are always router to the server that "owns"
their session
5. When a server fails, mod_jk detect this and forwards requests to
one of the other members of the cluster
6. When the failed node comes back up, it re-joins the cluster and
everything goes back to normal
Note that you can either implement sticky sessions (as I have described
above), or you can use session replication across your cluster. I'm not
a big fan of session replication because of all the messages that need
to be sent around. For my production purposes, requiring a user to login
again when failover occurs is acceptable. For me, the complexity of
session replication is not necessary. Your requirements may differ.
For more information on mod_jk balancing and clustering, see this page:
http://tomcat.apache.org/connectors-doc/generic_howto/loadbalancers.html
This page presupposes an understanding of how mod_jk is configured. If
you haven't used mod_jk before, start here:
http://tomcat.apache.org/connectors-doc/
and read the links for "All about workers", "For the impatient", and the
reference guide for Apache. If you have more questions, post back to the
list.
> What extra hardware and/or software do I need?
You'll want a hardware load-balancer to balance between web1 and web2.
As for software, just adding mod_jk to the mix should do it.
- -chris
-----BEGIN PGP SIGNATURE-----
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7EsAn0N3dM9qCB5thWTq0aFIiJEhbr/I
=pM8p
-----END PGP SIGNATURE-----
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