Welcome!

Weblogic Authors: Elizabeth White, Michael Meiner, Michael Bushong, Avi Rosenthal

Related Topics: Weblogic

Weblogic: Article

'HTTP Session Replication Failure' Issues

Moving away from the primary thought

Sometimes, HTTP session states are not replicated from the primary server to the secondary server.

Symptoms

  1. The application using HTTP session does not function as designed and you see a loss of session data.
  2. You might be asked to re-log into the application even when the session has still not timed out.
  3. You see errors and warnings related to HTTP session failures in the server's log file.
  4. The request is not failed over to another server properly.

There are several reasons as to why session replication fails. We will look at ways to diagnose the issue, possible reasons for it, and the ways to address them.

Types of HTTP Session Replication
There are five different implementations of session persistence:

  • Memory (single-server, non-replicated): When you use memory-based storage, all session information is stored in memory and is lost when you stop and restart WebLogic Server.
  • File system persistence: Session information is stored in a file under the PersistentStoreDir specified.
  • JDBC persistence: Session information is stored in a database table.
  • Cookie-based session persistence: Session information is stored in a cookie.
  • In-memory replication (across a cluster): Session data is copied from one server instance to another into memory.

Diagnosing the Issue
Consider a scenario with two servers (MyServer-1, MyServer-2) in a cluster. When you enable the debug flags (see the "Enable the Debug Flags to Track Session Replication Failures"section), you will see the messages below when a request from a client is sent the very first time.

On MyServer-1:

<Oct 9, 2003 12:38:21 PM PDT> <Debug> <Cluster> <000000>
<Creating primary 5165892837402719733>
<Oct 9, 2003 12:38:21 PM PDT> <Debug> <Cluster> <000000>
<Created secondary for 5165892837402719733 on -7957889153726652135S:
192.168.11.112: [9001,9001, -1, -1,9001, -1, -1]: mydomain: MyServer-2>

This logging message means that the primary server is MyServer-1 and a secondary has been created on MyServer-2. A message like the one shown below will be logged on MyServer-2 to confirm that.

ExecuteThread: '1' for queue: 'Replication'> <kernel identity> <>
<000000> <Creating secondary 5165892837402719733>
####<Oct 9, 2003 12:38:21 PM PDT> <Debug> <Cluster>
<rvimala-c840> <MyServer-2> <ExecuteThread:
'1' for queue: 'Replication'>
<kernel identity> <> <000000>
<Updated local secondary of 5165892837402719733>

If you check the JSESSIONID it looks like:

JSESSIONID=1E9Xwn7nLYfOsc1obgRZIwW5s72an7HPPvSD7iaWHMXzpHga5cQj
!-1587343083!-1587348922

JSESSIONID is the default name of the cookie, which could be changed to anything in weblogic.xml. The format of JSESSIONID is

SessionId!PrimaryServer JVM Hash!SecondaryServer JVMHash

Every time data is changed (either set/get or removed) in the session you'll see the logging message.

On MyServer-1:

<Oct 9, 2003 12:38:21 PM PDT> <Debug> <Cluster> <000000>
<Updated remote secondary for 5165892837402719733>

On MyServer-2:

####<Oct 9, 2003 12:38:21 PM PDT> <Debug> <Cluster>
<rvimala-c840> <MyServer-2> <ExecuteThread:
'1' for queue: 'Replication'> <kernel identity> <> <000000>
<Updated local secondary of 5165892837402719733>

If for any reason session replication fails, you will see the message below in the MyServer-1 log:

<Nov 6, 2003 12:59:12 PM EST> <Debug> <Cluster> <000000>
<Unable to create secondary for -5165892837402719733>
<Nov 6, 2003 12:59:12 PM EST> <Debug> <Cluster> <000000>
<Error creating secondary 5165892837402719733 on -7957889153726652135S:
192.168.11.112:[9001,9001,-1,-1,9001,-1,-1]:mydomain:MyServer-2>

And, the JSESSIONID would appear as

JSESSIONID=1E9Xwn7nLYfOsc1obgRZIwW5s72an7HPPvSD7iaWHMXzpHga5cQj!-1587343083!NONE

The secondary server hash would become NONE

Enable the Debug Flags to Track Session Replication Failures
You can enable the flags DebugCluster, DebugClusterAnnouncements, DebugFailOver, DebugReplication, and DebugReplicationDetails.

To Enable
Use the weblogic.Admin command-line utility to dynamically turn the debug options on and off. For example, to turn on DebugCluster on all administration instances of ServerDebug MBean (i.e., Admin Server or al Managed Server):

java weblogic.Admin -url t3://localhost:7001 -username system -password weblogic
SET -type ServerDebug -property DebugCluster true

Or, edit the config.xml and the MBean element in the <ServerDebug/> stanza for each server that you want to debug and set it to a value of "true" to enable or "false" to disable. Then you must restart the Admin Server. Managed Servers will reconnect to the Admin Server and the debug flags will then dynamically take effect. For example:

<ServerDebug DebugCluster="true" Name="myserver"/>

At the end, with all the flags set, in your config.xml the ServerDebug tag would look like:

<ServerDebug ClassFinder="true" DebugCluster="true"
DebugClusterAnnouncements="true" DebugFailOver="true"
DebugReplication="true" DebugReplicationDetails="true" Name="MyServer1"/>

Make sure the stdOutSeverity level of the server is INFO and StdoutDebugEnabled is set to "true". The debug information will be logged into the server log as well as to the standard out.

Checklist for Each Session Persistence Type
Memory (Single Server, Nonreplicated)

  1. When you use memory-based storage, all session information is stored in memory and is lost when you stop and restart BEA WebLogic Server.
  2. Make sure you have allocated sufficient heap size when running WebLogic Server; otherwise, your server may run out of memory under heavy load.
  3. Not a recommended type for Cluster configuration (because the data is kept in heap and is not available to any other server).

File System Persistence

  1. Verify that the directory where BEA WebLogic Server stores the sessions is correctly specified in weblogic.xml. You must also create this directory yourself and make sure appropriate access privileges have been assigned to the directory.
  2. Make sure you have enough disk space.

JDBC Persistence
Make sure the connection pool that connects to the database has read/write access for the database table used.

Cookie-Based Persistence

  1. Make sure you have not stored anything other than java.lang.String in the HTTP session.
  2. Do not flush the HTTP response object in your application code.
  3. Make sure that the content length of the response exceeds the buffer size set (default is 8192 bytes).
  4. Make sure that cookies are enabled in the browser.
  5. Make sure that you do not use commas (,) in a string when using cookie-based session persistence.

In-Memory Replication

  1. Make sure that the BEA WebLogic Server is accessed only via a proxy server or a hardware load balancer
  2. The hardware load balancer should support a compatible passive or active cookie persistence mechanism, and SSL persistence.
  3. Recommended type in a cluster.

Validate the weblogic.xml Entries
Make sure weblogic.xml has all the parameters that need to be set for each Session Replication type. For example, when using in-memory replication the sample weblogic.xml would look like:

<session-descriptor> <session-param> <param-name> PersistentStoreType </param-name> <param-value> replicated </param-value> </session-param> </session-descriptor>

Note: The debug files are subjected to change with each version of BEA WebLogic Server.

Session Data Must Be Serializable
To support in-memory replication of HTTP session states, all servlet and JSP session data must be serializable or else session replication would fail.

When debugging is enabled, BEA WebLogic Server would output the warning messages below by indicating that the session is not replicated. After this, session replication would stop.

Debug Message:

<Oct 8, 2003 2:10:45 PM PDT> <Error> <Cluster> <000126>
<All session objects should be serializable to replicate.
Please check the objects in your session.
Failed to replicate non-serializable object>

On the subsequent request the JSESSIONID will be missing the secondary server and will be marked NONE, e.g.:

JSESSIONID=1E9Xwn7nLYfOsc1obgRZIwW5s72an7HPPvSD7iaWHMXzpHga5cQj!-1587343083!NONE

Solution: Find out the page the error is thrown from and make sure that all the data put into the session is serializable.

Check for Network/Multicast Issues
Make sure that the network is fine and there are no multicast issues. Do the multicast test to make sure that the multicast IP is working fine.

Syntax

java utils.MulticastTest -n name -a address [-p portnumber] [-t timeout] [-s send]

(http://edocs.bea.com/wls/docs81/adminref/utils.html#1199798)

Validate Cluster Configuration
The primary and secondary servers are selected from the cluster list. In a cluster of two servers, if the cluster doesn't have all the servers, then a secondary might not be chosen, resulting in the session data not being replicated.

To verify, execute the following commands:

  1. Make sure weblogic.jar is in the classpath.
  2. To get all the servers in a cluster:

java weblogic.Admin -username weblogic -password weblogic -url
http://oneofthemanagedserverurlinthecluster:7001/ GET -type ClusterRuntime -pretty

This will list all the servers in a cluster. The URL could be changed to every server in the cluster to make sure they all have the same entries.

Application Code Diagnostics
Make sure you use only setAttribute/removeAttribute methods of the HTTP session in your application code to update the HTTP session. If you use other set methods to change objects within a session, BEA WebLogic Server does not replicate those changes.

Please do not use the methods putValue and removeValue of the HTTP session as they are deprecated and there could be issues with session data replication when using such methods in your application. Instead, use only the setAttribute/removeAttribute methods of the Http session.

Cookies vs URL Rewriting
In some situations, a browser or wireless device may not accept cookies, which makes session tracking with cookies impossible. URL rewriting is a solution to this situation that can be substituted automatically when WebLogic Server detects that the browser does not accept cookies. Enable URL rewriting in BEA WebLogic Server by setting the URLRewritingEnabled attribute in the WebLogic-specific deployment descriptor, weblogic.xml, under the <session-param> element. The default value for this attribute is true.

Performance Issues

  • Consider serialization overhead: Serializing session data introduces some overhead for replicating the session state. The overhead increases as the size of the serialized objects grows. If you plan to create very large objects in the session, test the performance of your servlet to ensure that performance is acceptable.
  • Control frame access to session data: If you are designing a Web application that utilizes multiple frames, keep in mind that there is no synchronization of requests made by frames in a given frameset. For example, it is possible for multiple frames in a frameset to create multiple sessions on behalf of the client application, even though the client should logically create only a single session.

    To avoid unexpected application behavior, carefully plan how you access session data with frames. You can apply one of the following general rules to avoid common problems:
    - In a given frameset, ensure that only one frame creates and modifies session data.
    - Always create the session in a frame of the first frameset your application uses (for example, create the session in the first HTML page that is visited). After the session has been created, access the session data only in framesets other than the first frameset.

  • Storing larger amounts of data in the session: JDBC persistence and File persistence won't be faster as the session data has to be stored and retrieved from an external resource. There is also a performance overhead because of JDBC access for each session update. If you want to store large objects in the session, then JDBC or File persistence should be considered.
  • Storing small amount of data in the session: Cookie-based session persistence is most useful when you do not need to store large amounts of data in the session. Cookie-based session persistence can make managing your BEA WebLogic Server installation easier because clustering failover logic is not required.

    Further Information
    For additional information go to http://support.bea.com for some published solutions on session replication failures. You can also query ASK BEA at http://websupport.beasys.com/index.jsp.

    If none of these help you towards a solution or an identifier in your application, then contact BEA Customer Support for further diagnosis. You can open a case with a valid support contract by logging in at http://support.bea.com/login.jsp

  • More Stories By Vimala Ranganthan

    Vimala Ranganathan is a backline developer relations engineer with BEA Systems. She specializes in troubleshooting and solving complex customer issues with their mission-critical applications on BEA products. Vimala holds a bachelor's degree in computer science.

    Comments (0)

    Share your thoughts on this story.

    Add your comment
    You must be signed in to add a comment. Sign-in | Register

    In accordance with our Comment Policy, we encourage comments that are on topic, relevant and to-the-point. We will remove comments that include profanity, personal attacks, racial slurs, threats of violence, or other inappropriate material that violates our Terms and Conditions, and will block users who make repeated violations. We ask all readers to expect diversity of opinion and to treat one another with dignity and respect.


    @ThingsExpo Stories
    "IoT is going to be a huge industry with a lot of value for end users, for industries, for consumers, for manufacturers. How can we use cloud to effectively manage IoT applications," stated Ian Khan, Innovation & Marketing Manager at Solgeniakhela, in this SYS-CON.tv interview at @ThingsExpo, held November 3-5, 2015, at the Santa Clara Convention Center in Santa Clara, CA.
    "We're a cybersecurity firm that specializes in engineering security solutions both at the software and hardware level. Security cannot be an after-the-fact afterthought, which is what it's become," stated Richard Blech, Chief Executive Officer at Secure Channels, in this SYS-CON.tv interview at @ThingsExpo, held November 1-3, 2016, at the Santa Clara Convention Center in Santa Clara, CA.
    Information technology is an industry that has always experienced change, and the dramatic change sweeping across the industry today could not be truthfully described as the first time we've seen such widespread change impacting customer investments. However, the rate of the change, and the potential outcomes from today's digital transformation has the distinct potential to separate the industry into two camps: Organizations that see the change coming, embrace it, and successful leverage it; and...
    Data is the fuel that drives the machine learning algorithmic engines and ultimately provides the business value. In his session at Cloud Expo, Ed Featherston, a director and senior enterprise architect at Collaborative Consulting, discussed the key considerations around quality, volume, timeliness, and pedigree that must be dealt with in order to properly fuel that engine.
    Internet of @ThingsExpo, taking place June 6-8, 2017 at the Javits Center in New York City, New York, is co-located with the 20th International Cloud Expo and will feature technical sessions from a rock star conference faculty and the leading industry players in the world. @ThingsExpo New York Call for Papers is now open.
    What happens when the different parts of a vehicle become smarter than the vehicle itself? As we move toward the era of smart everything, hundreds of entities in a vehicle that communicate with each other, the vehicle and external systems create a need for identity orchestration so that all entities work as a conglomerate. Much like an orchestra without a conductor, without the ability to secure, control, and connect the link between a vehicle’s head unit, devices, and systems and to manage the ...
    We are always online. We access our data, our finances, work, and various services on the Internet. But we live in a congested world of information in which the roads were built two decades ago. The quest for better, faster Internet routing has been around for a decade, but nobody solved this problem. We’ve seen band-aid approaches like CDNs that attack a niche's slice of static content part of the Internet, but that’s it. It does not address the dynamic services-based Internet of today. It does...
    20th Cloud Expo, taking place June 6-8, 2017, at the Javits Center in New York City, NY, will feature technical sessions from a rock star conference faculty and the leading industry players in the world. Cloud computing is now being embraced by a majority of enterprises of all sizes. Yesterday's debate about public vs. private has transformed into the reality of hybrid cloud: a recent survey shows that 74% of enterprises have a hybrid cloud strategy.
    Everyone knows that truly innovative companies learn as they go along, pushing boundaries in response to market changes and demands. What's more of a mystery is how to balance innovation on a fresh platform built from scratch with the legacy tech stack, product suite and customers that continue to serve as the business' foundation. In his General Session at 19th Cloud Expo, Michael Chambliss, Head of Engineering at ReadyTalk, discussed why and how ReadyTalk diverted from healthy revenue and mor...
    The 20th International Cloud Expo has announced that its Call for Papers is open. Cloud Expo, to be held June 6-8, 2017, at the Javits Center in New York City, brings together Cloud Computing, Big Data, Internet of Things, DevOps, Containers, Microservices and WebRTC to one location. With cloud computing driving a higher percentage of enterprise IT budgets every year, it becomes increasingly important to plant your flag in this fast-expanding business opportunity. Submit your speaking proposal ...
    You have great SaaS business app ideas. You want to turn your idea quickly into a functional and engaging proof of concept. You need to be able to modify it to meet customers' needs, and you need to deliver a complete and secure SaaS application. How could you achieve all the above and yet avoid unforeseen IT requirements that add unnecessary cost and complexity? You also want your app to be responsive in any device at any time. In his session at 19th Cloud Expo, Mark Allen, General Manager of...
    The Internet of Things (IoT) promises to simplify and streamline our lives by automating routine tasks that distract us from our goals. This promise is based on the ubiquitous deployment of smart, connected devices that link everything from industrial control systems to automobiles to refrigerators. Unfortunately, comparatively few of the devices currently deployed have been developed with an eye toward security, and as the DDoS attacks of late October 2016 have demonstrated, this oversight can ...
    "ReadyTalk is an audio and web video conferencing provider. We've really come to embrace WebRTC as the platform for our future of technology," explained Dan Cunningham, CTO of ReadyTalk, in this SYS-CON.tv interview at WebRTC Summit at 19th Cloud Expo, held November 1-3, 2016, at the Santa Clara Convention Center in Santa Clara, CA.
    Major trends and emerging technologies – from virtual reality and IoT, to Big Data and algorithms – are helping organizations innovate in the digital era. However, to create real business value, IT must think beyond the ‘what’ of digital transformation to the ‘how’ to harness emerging trends, innovation and disruption. Architecture is the key that underpins and ties all these efforts together. In the digital age, it’s important to invest in architecture, extend the enterprise footprint to the cl...
    Bert Loomis was a visionary. This general session will highlight how Bert Loomis and people like him inspire us to build great things with small inventions. In their general session at 19th Cloud Expo, Harold Hannon, Architect at IBM Bluemix, and Michael O'Neill, Strategic Business Development at Nvidia, discussed the accelerating pace of AI development and how IBM Cloud and NVIDIA are partnering to bring AI capabilities to "every day," on-demand. They also reviewed two "free infrastructure" pr...
    "Dice has been around for the last 20 years. We have been helping tech professionals find new jobs and career opportunities," explained Manish Dixit, VP of Product and Engineering at Dice, in this SYS-CON.tv interview at 19th Cloud Expo, held November 1-3, 2016, at the Santa Clara Convention Center in Santa Clara, CA.
    More and more brands have jumped on the IoT bandwagon. We have an excess of wearables – activity trackers, smartwatches, smart glasses and sneakers, and more that track seemingly endless datapoints. However, most consumers have no idea what “IoT” means. Creating more wearables that track data shouldn't be the aim of brands; delivering meaningful, tangible relevance to their users should be. We're in a period in which the IoT pendulum is still swinging. Initially, it swung toward "smart for smar...
    Extracting business value from Internet of Things (IoT) data doesn’t happen overnight. There are several requirements that must be satisfied, including IoT device enablement, data analysis, real-time detection of complex events and automated orchestration of actions. Unfortunately, too many companies fall short in achieving their business goals by implementing incomplete solutions or not focusing on tangible use cases. In his general session at @ThingsExpo, Dave McCarthy, Director of Products...
    Successful digital transformation requires new organizational competencies and capabilities. Research tells us that the biggest impediment to successful transformation is human; consequently, the biggest enabler is a properly skilled and empowered workforce. In the digital age, new individual and collective competencies are required. In his session at 19th Cloud Expo, Bob Newhouse, CEO and founder of Agilitiv, drew together recent research and lessons learned from emerging and established compa...
    Businesses and business units of all sizes can benefit from cloud computing, but many don't want the cost, performance and security concerns of public cloud nor the complexity of building their own private clouds. Today, some cloud vendors are using artificial intelligence (AI) to simplify cloud deployment and management. In his session at 20th Cloud Expo, Ajay Gulati, Co-founder and CEO of ZeroStack, will discuss how AI can simplify cloud operations. He will cover the following topics: why clou...