Servlet cluster, Object cluster & Firewall

          Hi,
          WLS 5.1 have a firewall restriction : no firewall between the servlet cluster and the object cluster. Is this restristion stay in WLS 6.0 ?
          Thanks.
          Ernest Remanjon
          Related documentation: Using Weblogic server clusters, version 1.1, October 2000, pg 3-19.

Hi,
          This issue has come up several times -- hopefully, we will update our documentation to clarify the issues.
          The answer is that WLS (i.e., any version) does not care about firewalls in general, what it cares about are any load-balancing and/or network
          address translation features of the firewalls. Let's take the easy one first.
          Network-address translation issues
          =========================
          WebLogic uses the IP address of the machine where the server is running to pass information back to the caller (e.g., the RMI stub has
          information about the location of the object, the Session ID has information encoded in it about the location of the HttpSession object).
          Therefore, if the caller uses a different IP address (the one that maps to the firewall) than the physical IP address of the machine where the
          server is running, you need to tell WebLogic what the "external" IP address is so that it will use this when encoding location information. I
          don't remember exactly when this capability was added but you control it via the weblogic.system.DNSName property in later versions of the
          product.
          Load-balancing issues
          ================
          WebLogic offers the capability of using stateful objects -- objects that reside on a particular server in the cluster. The information about
          the location of these stateful objects is passed back to the caller so that the callers next request can be routed back to the correct
          location. If, there is some network device between the caller and the server that causes the request to be routed to a server other than the
          one containing the object, this will cause the application not to work.
          For example, I have a stateful session bean instance residing in Server A in my cluster for a particular caller. However, I have set my
          weblogic.system.DNSName property in my server to map to the IP address of my load-balancing hardware device so that the stub sends the caller's
          request to the load-balancer instead of Server A. Now, if the load-balancer (for whatever reason) decides to route the request to some other
          server in my cluster (i.e., not Server A), the call is going to fail because the server receiving the call has no knowledge of the stateful
          session bean instance.
          Therefore, in whatever architecture you choose, you need to make sure that you do not use a hardware load-balancer (or even DNS round-robining)
          at the point where calls must be routed to a particular server. There are a couple of popular configurations, I will start with the one I
          always recommend to my customers first.
          Internet ---> firewall and/or hardware load-balancer ---> Web (Proxy) Servers ---> firewall ----> WLS Cluster (Servlets/JSPs and EJBs)
          The one you are describing can be done multiple ways, none of which I recommend unless you have some outstanding reason for needing this
          architecture.
          Internet ---> firewall and/or hardware load-balancer ---> Web (Proxy) Servers ---> WLS Cluster (Servlets/JSPs) ---> firewall ---> WebLogic
          Cluster (EJBs)
          Internet ---> firewall and/or hardware load-balancer ---> Web (Proxy) Servers ---> firewall ----> WLS Cluster (Servlets/JSPs) ---> firewall (or
          not) ---> WebLogic Cluster (EJBs)
          Hope this clarifies the issues,
          Robert
          Ernest Remanjon wrote:
          > Hi,
          >
          > WLS 5.1 have a firewall restriction : no firewall between the servlet cluster and the object cluster. Is this restristion stay in WLS 6.0 ?
          >
          > Thanks.
          >
          > Ernest Remanjon
          >
          > Related documentation: Using Weblogic server clusters, version 1.1, October 2000, pg 3-19.

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Servlet applet object io streams

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another weird thing that i found out.
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Sorry folks, just found my error. Forgot about the ObjectInputStream waiting on the Servlet side, so of course had a dead look...
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Applet-servlet communication, object serialization, problem

hi,
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I try to build an applet-servlet communication using serialized objects. In my test scenario i write a serialized standard java object (e.g. a String object) onto the ObjectOutputStream of the applet/test-application (it doesn't matters wheter to use the first or the latter one for test cases) and the doPost method of the servlet reads the object from the ObjectInputStream. That works fine. But if i use customized objects (which should also work fine) the same code produces an classnotfound exception. When i try to read and cast the object:
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hi, thanks for the reply,
all my classes are in the web-inf/classes of the web-app and have an appropriate package structure. thus the TestMessage class is inside a package.
i tried some names for the testclass but it didn't matter. the exception stays the same. I also tried to put the jar in the common/lib but the problem stays.
Well the problem with loaded classes: As i mentioned in the post above i can instantiate an object of TestMessage in the code without any problems (so the classloader of my webapp should know the class!!)
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strange behaviour...
p.s. sending the same object from the servlet to the client works well
regards
daniel
Message was edited by:
theazazel

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Best regards,
Ryan LeCompte
[email protected]
http://www.louisiana.edu/~rml7669
"Linus Nikander" <[email protected]> wrote:
Is it possible to accesss objects stored in a Servlet session context
from
an EJB ? If so, how ?
//Linus Nikander - [email protected]

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[att1.html]


Patrick Power wrote:
          > Thanx for your reply Prasad. I was surprised none of the Bea engineers
          > wished to touch this one. What do you suppose is up with that? Either
          > they are too busy, or possibly my question is too dumb.
          >
          I am from BEA so its not that we are not responding ;).
          >
          > Back to the issue: Yes, we will NES bridge/proxy into servlet front-end
          > cluster, potentially with Directors on the very front of the topology for
          > balancing. Your diagram as such:
          >
          > <Netscape/IIS/Apache/WLS FRONT END> ----- <CLUSTER OF WEBLOGIC SERVER
          > > SERVING SERVLETS> --- <CLUSTER OF WEBLOGIC SERVERS SERVING EJB>
          >
          > 1) Does <Netscape/IIS/Apache/WLS FRONT END> mean NES with proxy shared lib,
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          Yes.
          >
          > 2) I would assume that <CLUSTER OF WEBLOGIC SERVERS SERVING SERVLETS> would
          > need the WLS HttpClusterServlet to the <CLUSTER OF WEBLOGIC SERVERS SERVING
          > EJB> all the way in the back.
          No. I was splitting presentation logic (namely servlets and jsp) and business
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          colocate them both together. You could use NES or IIS or Apache or WLS. You
          don't need HttpClusterServlet.
          Lets get this straight.
          1. You need our proxy plugin for failover and to load balance the request that
          are going to presentation logic.
          2. From presentation logic layer, when you talk to backend business logic
          providers (like ejb cluster), if you use stateless session beans we provide
          failover and load balancing. In future we will support clustered stateful
          session beans as well. Therefore you don't need load balancer here.
          3. HttpClusterServlet should run only in front of presentation logic cluster and
          also it supports http only.
          Hope this helps.
          - Prasad
          > The NES proxy would only proxy into the f/e
          > cluster, right? You're not suggesting an external proxy of some type, are
          > you? The HttpClusterServlet is for WLS cluster-to-cluster proxies.
          > 3) A load balancer between the wls f/e and wls b/e clusters? That doesn't
          > seem applicable here. Once again, it should be HttpClusterServlet for WLS
          > cluster-to-cluster proxies.
          > 4) "use two or three proxy servers to avoid single point of failure."
          > Hmmm, once again - are we talking the WLS HttpClusterServlet proxy? Well,
          > that's the inital question: Can I have more than one HttpClusterServlet
          > proxy in the front-end cluster, proxying to the back-end cluster?
          > Otherwise, internally from this WLS architecture perspective, it is a single
          > point of failure.
          >
          > An example: 10 instances in f/e cluster. can more than one of these
          > instances have the WLS HttpClusterServlet proxy to the b/e cluster? Or, are
          > there instances of WLS HttpClusterServlet proxy in all 10 f/e cluster
          > instances?
          >
          > Cheers, Pat
          >
          > Prasad Peddada <[email protected]> wrote in message
          > news:[email protected]...
          > >
          > >
          > > Patrick Power wrote:
          > >
          > > > I know that this topic was addressed to some degree here in an earlier
          > > > posting, but I still have a question regarding the architecture
          > > > design:
          > > >
          > > > If configuring a front-end cluster for servlets/sessions and a
          > > > back-end cluster for remote services -- you route requests to the
          > > > back-end using the WLS proxy servlet. ok, got that part.
          > >
          > > Not quite. The typical scenario is
          > >
          > > <Netscape/IIS/Apache/WLS FRONT END> ----- <CLUSTER OF WEBLOGIC SERVER
          > > SERVING SERVLETS> --- <CLUSTER OF WEBLOGIC SERVERS SERVING EJB>
          > >
          > > You don't proxy and serve servlets from the same server.
          > >
          > > >
          > > > The question: Is there a single instance of the wls proxy servlet in
          > > > the front-end cluster? Or, is it on every instance in the front-end
          > > > cluster? What is the failover mechanism, in the case of a single
          > > > instance of proxy servlet in the f-e cluster failing?
          > >
          > > To prevent that you need to use some kind of h/w or software load
          > > balancer and then use two or three proxy servers to avoid single point
          > > of failure.
          > >
          > > > Is it a single point of failure between the 2 clusters?
          > > >
          > > > Thanx in advance for your help.
          > > >
          > > > BTW, I think Wei, Kumar and the other Bea folks cruising this group
          > > > have been doing a bang-up job of providing badly-needed detail on this
          > > > subject area - material this largely absent from the documentation.
          > > > Good job.
          > > >
          > > >
          > >
          > > --
          > > Cheers
          > >
          > > - Prasad
          > >
          > >

Round Robin doesn't work in Bea Weblogic Cluster

hello!
          we are using a weblogic (V5.1 SP8) cluster in the following configuration:
          2 Weblogic App-Servers as Servlet Containers.
          4 Weblogic App-Servers as EJB Containers.
          if a client connects to the first servlet - server, round robin between the
          4 EJB-servers behind doesn't work. It seems that the servlet-server is
          pinned to one EJB-server all the time.
          If we kill the second servlet-server as from now on round robin works in the
          EJB-server cluster like we expected.
          As we changed this configuration and also use an IPlanet webserver (one
          instance) with the weblogic proxy-plugin which connects to the
          servlet-cluster (2 instances)... round robin is working properly in the
          EJB-server cluster when the client connects to the IPlanet-server....
          what is the problem, why doesn't round robin work in the first
          configuration? any suggestions?
          Torsten Jenkner


Okay, is it that the round-robining is not perfect (i.e., it doesn't send the
          first request to server1 and the second request to server2 and so on) or is it
          sending every request to one server?
          Torsten Jenkner wrote:
          > yes exactly Robert that's it!
          >
          > Torsten
          >
          > "Robert Patrick" <[email protected]> schrieb im Newsbeitrag
          > news:[email protected]...
          > > I don't understand this. Are you saying that with servlet node 1 or
          > servlet
          > > node 2 running by themselves that RR works fine but once you start both
          > > together, it does not?
          > >
          > > This sounds like a case for support...
          > > Robert
          > >
          > > Torsten Jenkner wrote:
          > >
          > > > > > it is always the same stub in our case. Also the round robin in the
          > EJB
          > > > > > cluster does with the same java classes but does not if the servlet
          > > > cluster
          > > > > > consits of two nodes. So it seems to be a configuration problem, but
          > > > which
          > > > > > one?
          > > > >
          > > > > Hmm.... I don't quite understand this last statement about the EJB
          > and
          > > > servlet
          > > > > cluster, could you explain a little more?
          > > > >
          > > > > Thanks,
          > > > > Robert
          > > > >
          > > >
          > > > if you use 2 servlet cluster nodes round robin between the
          > servlet-cluster
          > > > and the ejb-cluster doesn't work. if i kill the second servlet-node it
          > works
          > > > fine. so my thought was it has to be a configuration problem, because RR
          > > > does with one servlet-node. ok?
          > > >
          > > > Torsten Jenkner
          > >

How is object handled with servlets?

Hi!
This is probably a very basic question, but I need to know. Does a servlet treat objects differently from any other Java class?
Consider you have the following class:
public class ClassC {
     private String strName = "John";
     public String getName() {
          return strName;
     public void setName(String name) {
          strName = name;
}Then we use a servlet to create a object of class ClassC:
     public void doGet(HttpServletRequest request, HttpServletResponse response)
               throws ServletException, IOException {
          String strFirstName= "Steve";
          ClassC c = new ClassC();
          c.setName("Lance");
          strFirstName = c.getName();
          response.setContentType("text/html");
          PrintWriter out = response.getWriter();
          out.println("<!DOCTYPE HTML PUBLIC \"-//W3C//DTD HTML 4.01 Transitional//EN\">");
          out.println("<HTML>");
          out.println(" <HEAD><TITLE>A Servlet</TITLE></HEAD>");
          out.println(" <BODY>");
          out.println("strFirstName = " + strFirstName);
          out.println(" </BODY>");
          out.println("</HTML>");
          out.flush();
          out.close();
     } My question is what �out.println("strFirstName = " + strFirstName);� will print in a server on the webb?
Suppose you have a produced a ResultSet and you put that as a private variable in a class as in ClassC above. Suppose I use the same technique as in the doGet-method, and have methods that extract data from the ResultSet. Will each use user of the servlet get unique information or will every user get the same information?
I think (and hope) that each user will get unique information. Is this correct?
Regards
Jonas

As written... the object Class is local to to the doGet method. This means that each run of the doGet method gets its own instance of the object, and each user will get their own data.
If strFirstName or c was declared as a class member, then all users would get the same data (potentially):
//bad servlet:
String strFirstName = "Steve";
ClassC c;
public void doGet(...) ... {
    c = new ClassC();
}

Servlet cluster, Object cluster & Firewall

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