Load Balancing of 2-Tiered vs 3-Tiered Clustering

Question

Hi,
          I was looking at the cluster diagrams on the clustering page:
          http://www.weblogic.com/docs60/cluster/index.html
          And I can't help notice a slight descrepency between the diagram of a 2-Tier
          cluster (WL web cluster + WL app cluster) vs.a 3-Tier cluster (web
          proxy-plugin + WL web cluster + WL app cluster).
          In the 2-Tier diagram, the arrows going from the web nodes to the app nodes
          converges to a single point, indicating that there's load balancing of
          servlet calls to ejbs.
          In the 3-Tier diagram, the arrows from each web node point directly to an
          app node, which seems to indicate that there is a static one-to-one
          relationship, hence no load-balancing. Below the 3-Tier diagram, one of the
          described limitations of using standalone web server and proxy plug-ins is:
          a.. Limited Load Balancing Options: When you use proxy plug-ins or the
          HttpClusterServlet to access clustered servlets, the load balancing
          algorithm is limited to a simple round-robin strategy.
          I believe this is describe load balancing between the fire-wall and the
          proxy web servers. But what about the load balancing between the WL web
          servers and the app servers? Does it exist, or does one web server always
          assigned to one app server?
          Gene Chuang
          Join Kiko.com!
          

Answer 1

Currently, we only support clusters within the same subnet, as most routers
          can't handle multicast traffic. We are considering designs to relax this
          restriction in a future release.
          -Don
          Cameron Purdy wrote:
          > > 3) In WLAS6.0, you can specify how to pick the secondary server. Most
          > > important of all, pick a secondary server which is on the different
          > physical
          > > box than primary.
          >
          > ... and if you are using two different physical networks, make sure it is on
          > the other physical network. Any hints on how to do that?
          >
          > --
          > Cameron Purdy
          > Tangosol, Inc.
          > http://www.tangosol.com
          > +1.617.623.5782
          > WebLogic Consulting Available
          >
          > "Wei Guan" <[email protected]> wrote in message
          > news:[email protected]...
          > > Here is my understanding:
          > > 1) Proxy will route new sessions based on round-robins. Old sessions will
          > > route to the primary server.
          > > 2) Primary server will pick the secondary server.
          > > 3) In WLAS6.0, you can specify how to pick the secondary server. Most
          > > important of all, pick a secondary server which is on the different
          > physical
          > > box than primary.
          > >
          > >
          > > --
          > > Hope it helps.
          > >
          > > Cheers - Wei
          > >
          > >
          > > "Cameron Purdy" <[email protected]> wrote in message
          > > news:[email protected]...
          > > > Is it true that the proxy can only use round-robin to load-balance the
          > WL
          > > > cluster? I understand that, once selected for a session, the proxy will
          > > > always route requests to the primary server specified in the cookie or
          > URL
          > > > (or secondary), but in the case that no primary or secondary has been
          > > > assigned, can the proxy pick a destination server (which I assume
          > becomes
          > > > the primary) using an algorithm such as "random" (which is theoretically
          > > > superior to round-robin over time)? Also, who picks the secondary
          > server?
          > > > Is it the primary or the proxy?
          > > >
          > > > --
          > > > Cameron Purdy
          > > > Tangosol, Inc.
          > > > http://www.tangosol.com
          > > > +1.617.623.5782
          > > > WebLogic Consulting Available
          > > >
          > > >
          > > > "Don Ferguson" <[email protected]> wrote in message
          > > > news:[email protected]...
          > > > > Hi, comments in line.
          > > > >
          > > > > Gene Chuang wrote:
          > > > > >
          > > > > > Hi,
          > > > > >
          > > > > > I was looking at the cluster diagrams on the clustering page:
          > > > > >
          > > > > > http://www.weblogic.com/docs60/cluster/index.html
          > > > > >
          > > > > > And I can't help notice a slight descrepency between the diagram of
          > a
          > > > 2-Tier
          > > > > > cluster (WL web cluster + WL app cluster) vs.a 3-Tier cluster (web
          > > > > > proxy-plugin + WL web cluster + WL app cluster).
          > > > > >
          > > > > > In the 2-Tier diagram, the arrows going from the web nodes to the
          > app
          > > > nodes
          > > > > > converges to a single point, indicating that there's load balancing
          > of
          > > > > > servlet calls to ejbs.
          > > > > >
          > > > > > In the 3-Tier diagram, the arrows from each web node point directly
          > to
          > > > an
          > > > > > app node, which seems to indicate that there is a static one-to-one
          > > > > > relationship, hence no load-balancing.
          > > > >
          > > > > This is just an artifact of the drawing, not of the architecture. The
          > > > same
          > > > > load balancing would be performed between the web and app tiers
          > > regardless
          > > > > of whether or not there is a front end web server.
          > > > >
          > > > > > Below the 3-Tier diagram, one of the
          > > > > > described limitations of using standalone web server and proxy
          > > plug-ins
          > > > is:
          > > > > >
          > > > > > a.. Limited Load Balancing Options: When you use proxy plug-ins or
          > the
          > > > > > HttpClusterServlet to access clustered servlets, the load balancing
          > > > > > algorithm is limited to a simple round-robin strategy.
          > > > > >
          > > > > > I believe this is describe load balancing between the fire-wall and
          > > the
          > > > > > proxy web servers. But what about the load balancing between the WL
          > > web
          > > > > > servers and the app servers? Does it exist, or does one web server
          > > > always
          > > > > > assigned to one app server?
          > > > >
          > > > > This is not describing the load balancing between the firewall and the
          > > > > proxy web servers; we do not control of how that is performed. It is
          > > > > describing the load balancing between the proxy servers and the web
          > > tier.
          > > > > The diagram should really show that more clearly, as was done in the
          > > > 2-tier
          > > > > example.
          > > > >
          > > > > -Don
          > > > >
          > > > > >
          > > > > > --
          > > > > > Gene Chuang
          > > > > > Join Kiko.com!
          > > >
          > > >
          > >
          > >