Chapter 22, Troubleshooting

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Sometimes however the Excel configuration may have been changed so that you do not see this. For example, if you drag a data point into Excel and you get the first value, but then nothing after that, you may want to check the following settings. All rights reserved. I can't get a connection. License failure: License in use by master There are two possible reasons for this message: One Cascade DataHub is tunnelling to another DataHub on another computer and that DataHub is tunnelling back to the first. This document contains macros.

Enable them? From the Tools menu, choose Options to open the Options window. From the Edit menu, choose Links to open the Edit Links window. Command Line Options. Here is a brief explanation of some of the more common error messages you might encounter when using the OPC DataHub: License failure: License in use by master There are two possible reasons for this message: One Cascade DataHub is tunnelling to another DataHub on another computer and that DataHub is tunnelling back to the first.

The Cascade DataHub is tunnelling to itself. Here's a summary of each message, and what to do: This document contains macros. This workbook contains links. Update them? Remote data not accessible. Start the DataHub or Connect? Ensure that the Automatic option in Calculation is selected.

Ensure that the Update remote references option in Workbook options is selected. Then close the Options window. Ensure that the Automatic option for Update is selected. Set the number of owners for the distributed cache. The following command sets 5 owners. The default is 2. When using a SYNC caching strategy, the cost of replication is easy to measure and directly seen in response times since the request does not complete until the replication completes.

The ASYNC caching strategy is more difficult to measure, but it can provide better performance than the SYNC strategy when the duration between requests is long enough for the cache operation to complete. This is because the cost of replication is not immediately seen in response times.

If requests for the same session are made too quickly, the cost of replication for the previous request is shifted to the front of the subsequent request since it must wait for the replication from the previous request to complete. For rapidly fired requests where a subsequent request is sent immediately after a response is received, the ASYNC caching strategy will perform worse than the SYNC caching strategy. Consequently, there is a threshold for the period of time between requests for the same session where the SYNC caching strategy will actually perform better than the ASYNC caching strategy.

In real world usage, requests for the same session are not normally received in rapid succession.


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Instead, there is typically a period of time in the order of a few seconds or more between the requests. In this case, the ASYNC caching strategy is a sensible default and provides the fastest response times. The infinispan subsystem contains the async-operations , expiration , listener , persistence , remote-command , state-transfer , and transport thread pools. These pools can be configured for any Infinispan cache container. The following table lists the attributes you can configure for each thread pool in the infinispan subsystem and the default value for each.

The following is an example of the management CLI command to set the max-threads value to 10 in the persistence thread pool for the server cache container. Runtime statistics about Infinispan caches and cache containers can be enabled for monitoring purposes. Statistics collection is not enabled by default for performance reasons. Statistics collection can be enabled for each cache container, cache, or both. The statistics option for each cache overrides the option for the cache container. Enabling or disabling statistics collection for a cache container will cause all caches in that container to inherit the setting, unless they explicitly specify their own.

Enabling Infinispan statistics may have a negative impact on the performance of the infinispan subsystem. Statistics should be enabled only when required. You can enable or disable the collection of Infinispan statistics using the management console or the management CLI.

From the management console, navigate to the Infinispan subsystem from the Configuration tab, select the appropriate cache or cache container, and edit the Statistics enabled attribute. Use the below commands to enable statistics using the management CLI. An Infinispan cluster is built out of several nodes where data is stored. To prevent data loss if multiple nodes fail, Infinispan copies the same data over multiple nodes. This level of data redundancy is configured using the owners attribute. As long as fewer than the configured number of nodes crash simultaneously, Infinispan will have a copy of the data available.

However, there are potential catastrophic situations that could occur when too many nodes disappear from the cluster:. This splits the cluster in two or more partitions, or sub-clusters, that operate independently. In these circumstances, multiple clients reading and writing from different partitions see different versions of the same cache entry, which for many applications is problematic. There are ways to alleviate the possibility for the split brain to happen, such as redundant networks or IP bonding.

However, these only reduce the window of time for the problem to occur. The goal is to avoid situations in which incorrect data is returned to the user as a result of either split brain or multiple nodes crashing in rapid sequence. In a split brain situation, each network partition will install its own JGroups view, removing the nodes from the other partitions. We do not have a direct way to determine whether the cluster has been split into two or more partitions, since the partitions are unaware of each other.

Instead, we assume the cluster has split when one or more nodes disappear from the JGroups cluster without sending an explicit leave message. With partition handling disabled, each such partition would continue to function as an independent cluster. Each partition may only see a part of the data, and each partition could write conflicting updates in the cache.

With partition handling enabled, if we detect a split, each partition does not start a rebalance immediately, but first checks whether it should enter degraded mode instead:. The stable topology is updated every time a rebalance operation ends and the coordinator determines that another rebalance is not necessary. These rules ensure that at most, one partition stays in available mode, and the other partitions enter degraded mode.

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When a partition is in degraded mode, it only allows access to the keys that are wholly owned:. This guarantees that partitions cannot write different values for the same key cache is consistent , and also that one partition can not read keys that have been updated in the other partitions no stale data. Two partitions could start up isolated, and as long as they do not merge, they can read and write inconsistent data.

In the future, we may allow custom availability strategies e. Currently the partition handling is disabled by default. Use the following management CLI command to enable partition handling:. This allows scaling of the data layer independent of the application, and enables different JBoss EAP clusters, which may reside in various domains, to access data from the same JBoss Data Grid cluster.

The following example shows how to externalize HTTP sessions. However, in a managed domain, each server group requires a unique remote cache configured. For each distributable application, an entirely new cache must be created. It can be created in an existing cache container, for example, web. Define the location of the remote Red Hat JBoss Data Grid server by adding the networking information to the socket-binding-group.

Server Overload

In the following example, web is the name of the cache container and jdg is the name of the appropriate cache located in this container. Since Undertow makes use of asynchronous IO, the IO thread that is responsible for the connection is the only thread that is involved in the request.


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That same thread is also used for the connection made to the back-end server. This procedure assumes that you are running in a managed domain and already have the following configured:. The below steps load balance servers in a managed domain, but they can be adjusted to apply to a set of standalone servers. Be sure to update the management CLI command values to suit your environment. Adding the advertise security key allows the load balancer and servers to authenticate during discovery.

Use the following management CLI command to add a modcluster socket binding with the appropriate multicast address and port configured. To configure a static load balancer with Undertow, you need to configure a proxy handler in the undertow subsystem. To configure a proxy handler in Undertow, you need to do the following on your JBoss EAP instance that will serve as your static load balancer:.

When accessing lb. Once you have decided which web server and HTTP connector to use, see the appropriate section for information on configuring your connector:. You also will need to make sure that JBoss EAP is configured to accept requests from external web servers. JBoss EAP communicates with the web servers using a connector. Each of these modules varies in how it works and how it is configured.

The modules are configured to balance work loads across multiple JBoss EAP nodes, to move work loads to alternate servers in case of a failure event, or both. JBoss EAP supports several different connectors. The one you choose depends on the web server in use and the functionality you need. ISAPI connector. NSAPI connector. Detects deployment and undeployment of applications and dynamically decides whether to direct client requests to a server based on whether the application is deployed on that server.

Directs client requests to the container as long as the container is available, regardless of application status. This simplifies installation and configuration, and allows for a more consistent update experience. In the following procedure, substitute the protocols and ports in the examples with the ones you need to configure. Configure the instance-id attribute of Undertow. The external web server identifies the JBoss EAP instance in its connector configuration using the instance-id. Use the following management CLI command to set the instance-id attribute in Undertow. Each protocol needs its own listener, which is tied to a socket binding.

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Depending on your desired protocol and port configuration, this step may not be necessary. You can check whether the required listeners are already configured by reading the default server configuration:. To add a listener to Undertow, it must have a socket binding. The socket binding is added to the socket binding group used by your server or server group. The following management CLI command adds an ajp socket binding, bound to port , to the standard-sockets socket binding group.

The following management CLI command adds an ajp listener to Undertow, using the ajp socket binding. It uses a communication channel to forward requests from the Apache HTTP Server to one of a set of application server nodes. For more details on the specific configuration options of the modcluster subsystem, see the ModCluster Subsystem Attributes. Note that you must be logged in to access this tool. The IP address, port, and other settings in this file, shown below, can be configured to suit your needs.

You can disable advertising and to use a proxy list instead using the following procedure. The management CLI commands in the following procedure assume that you are using the full-ha profile in a managed domain. If you are using a profile other than full-ha , use the appropriate profile name in the command. Edit the httpd. Set the ServerAdvertise directive to Off to disable server advertisement. If your configuration specifies the AdvertiseFrequency parameter, comment it out using a character. Be sure to continue to the next step to provide the list of proxies.

Advertising will not be disabled if the list of proxies is empty. It is necessary to provide a list of proxies because the modcluster subsystem will not be able to automatically discover proxies if advertising is disabled. First, define the outbound socket bindings in the appropriate socket binding group. This server can be a standalone server or part of a server group in a managed domain. This is called the master. Worker nodes in a managed domain share an identical configuration across a server group. Worker nodes running as standalone servers are configured individually.

The configuration steps are otherwise identical. The management CLI commands in this procedure assume that you are using a managed domain with the full-ha profile. By default, the network interfaces all default to Every physical host that hosts either a standalone server or one or more servers in a server group needs its interfaces to be configured to use its public IP address, which the other servers can see. Use the following management CLI commands to modify the external IP addresses for the management , public , and unsecure interfaces as appropriate for your environment.

Set a unique host name for each host that participates in a managed domain. This name must be unique across slaves and will be used for the slave to identify to the cluster, so make a note of the name you use. Use the following management CLI command to set a unique host name. This example uses slave1 as the new host name. For more information on configuring a host name, see Configure the Name of a Host. For newly configured hosts that need to join a managed domain, you must remove the local element and add the remote element host attribute that points to the domain controller.

Use the following management CLI command to configure the domain controller settings. For more information, see Connect to the Domain Controller. Add a management user for each host with the username that matches the host name of the slave. Be sure to answer yes to the last question, that asks "Is this new user going to be used for one AS process to connect to another AS process?

Example add-user script output trimmed. You can specify the password by setting the secret value in the server configuration, getting the password from the vault, or passing the password as a system property. Use the following management CLI command to specify the secret value. You will need to reload the server. The --host argument is not applicable for a standalone server. When creating a password in the vault, it must be specified in plain text, not Baseencoded. The following examples use server.

Specify the system property for the password in the server configuration file. Use the following managemente CLI command to configure the secret identity to use the system property. You can set the server. Start the server and pass in the server. The password must be entered in plain text and will be visible to anyone who issues a ps -ef command. The password is in plain text and will be visible to anyone who has access to this properties file. The slave will now authenticate to the master using its host name as the username and the encrypted string as its password.

If you deploy a clustered application, its sessions are replicated to all cluster nodes for failover, and it can accept requests from an external web server or load balancer. Each node of the cluster discovers the other nodes using automatic discovery, by default. The load balancer will then send future requests to another worker node in the cluster. After creating a new cluster using JBoss EAP, you can migrate traffic from the previous cluster to the new one as part of an upgrade process.

In this task, you will see the strategy that can be used to migrate this traffic with minimal outage or downtime. Enabling this option means that all new requests made to a cluster node in any of the clusters will continue to go to the respective cluster node. Additionally use the aforementioned procedure and set their load-balancing group to ClusterNEW.

From this point on, only requests belonging to already established sessions will be routed to members of ClusterOLD load-balancing group. As soon as there are no active sessions within ClusterOLD group, we can safely remove its members. Using Stop Nodes would command the load balancer to stop routing any requests to this domain immediately.

This will force a failover to another load-balancing group which will cause session data loss to clients, provided there is no session replication between ClusterNEW and ClusterOLD. Contexts of these nodes will be disabled and once there are no active sessions present, they will be ready for removal. New clients' sessions will be created only on nodes with enabled contexts, presumably ClusterNEW members in this example. Stopping a context with waittime set to 0 , meaning no timeout, instructs the balancer to stop routing any request to it immediately, which forces failover to another available context.

If you set a timeout value using the waittime argument, no new sessions are created on this context, but existing sessions will continue to be directed to this node until they complete or the specified timeout has elapsed. The waittime argument defaults to 10 seconds. Disabling a context tells the balancer that no new sessions should be created on this context. The proxy server accepts client requests from the web front end, and passes the work to participating JBoss EAP servers. If sticky sessions are enabled, the same client request always goes to the same JBoss EAP server, unless the server is unavailable.

You can use this sample instead of creating your own file by removing the. Create a new file called conf. Add the following configuration to the file, making sure to modify the contents to suite your needs. A sample workers configuration file is provided at conf. In addition to the JKMount directive in the mod-jk.

A sample URI worker map configuration file is provided at conf. Add a line for each URL pattern to be matched, for example:. Update the configuration to point to uriworkermap. Append the following to conf. The JBoss EAP undertow subsystem needs to specify a listener in order to accept requests from and send replies back to an external web server. If you are using one of the default high availability configurations ha or full-ha , an AJP listener is already configured.

See the appropriate section below to configure a basic load-balancing or non-load-balancing proxy. Replace the values with ones appropriate to your setup. The example IP addresses are fictional. Replace them with the appropriate values for your environment. The examples above all communicate using the HTTP protocol. A sticky session means that if a client request originally goes to a specific JBoss EAP worker, all future requests will be sent to the same worker, unless it becomes unavailable.

This is almost always the recommended behavior. You can specify additional parameters to the ProxyPass statement, such as lbmethod and nofailover. Depending on the protocol that you will be using, you may need to configure a listener. If you are using one of the default high availability configurations ha or full-ha , an AJP listener is also preconfigured. It does not include configuration for load-balancing or high-availability failover. If you use a different directory, modify the instructions accordingly.

Copy the following contents into the file. If you do not want to use a rewrite. The uriworkermap. The following example file shows the syntax of the file. Place your uriworkermap. The workers. The following is an example of a workers. The worker names, worker01 and worker02 , must match the instance-id configured in the JBoss EAP undertow subsystem. The rewrite. The rewritten path is specified using name-value pairs, as shown in the example below. Restart your IIS server by using the net stop and net start commands. The following example file shows the syntax of the file, with a load-balanced configuration.

The configuration of the load balancer is covered in the next step. The load balancer is configured near the end of the file, to comprise workers worker01 and worker This ratio is derived from the load-balancing factor lbfactor assigned to each server. These extensions are known as server plugins. If your Oracle iPlanet configuration directory is different, modify the instructions accordingly.

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The configuration above is for a bit architecture. You can configure the NSAPI connector for a basic configuration, with no load balancing, or a load-balancing configuration.

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Choose one of the following options, after which your configuration will be complete. The redirection is done on a per-deployment and hence per-URL basis. The string jknsapi refers to the HTTP connector which will be defined in the next step.