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High_Availability_Guide.html
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<title>High Availability Guide</title>
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<body id="High_Availability_Guide" class="book toc2 toc-left">
<div id="header">
<h1>High Availability Guide</h1>
<div class="details">
<span id="author" class="author">WildFly clustering team</span><br>
<span id="revnumber">version 20.0.0.Final,</span>
<span id="revdate">2020-06-05T20:49:23Z</span>
</div>
<div id="toc" class="toc2">
<div id="toctitle">High Availability Guide</div>
<ul class="sectlevel1">
<li><a href="#Introduction_To_High_Availability_Services">1. Introduction To High Availability Services</a>
<ul class="sectlevel2">
<li><a href="#what-are-high-availability-services">1.1. What are High Availability services?</a></li>
<li><a href="#high-availability-through-fail-over">1.2. High Availability through fail-over</a></li>
<li><a href="#high-availability-through-load-balancing">1.3. High Availability through load balancing</a></li>
<li><a href="#aims-of-the-guide">1.4. Aims of the guide</a></li>
<li><a href="#organization-of-the-guide">1.5. Organization of the guide</a></li>
</ul>
</li>
<li><a href="#HTTP_Services">2. HTTP Services</a></li>
<li><a href="#Subsystem_Support">3. Subsystem Support</a></li>
<li><a href="#Infinispan_Subsystem">4. Infinispan Subsystem</a>
<ul class="sectlevel2">
<li><a href="#cache-container">4.1. Cache container</a></li>
<li><a href="#remote_cache_container">4.2. Remote Cache Container</a></li>
</ul>
</li>
<li><a href="#Distributable_Web_Applications">5. Distributable Web Applications</a>
<ul class="sectlevel2">
<li><a href="#distributable-web-subsystem">5.1. Distributable Web Subsystem</a></li>
<li><a href="#overriding-default-behavior">5.2. Overriding default behavior</a></li>
<li><a href="#distributable-shared-sessions">5.3. Distributable Shared Sessions</a></li>
<li><a href="#optimizing-performance-of-distributed-web-applications">5.4. Optimizing performance of distributed web applications</a></li>
<li><a href="#ranked-affinity-load-balancer">5.5. Enabling ranked affinity support in load balancer</a></li>
</ul>
</li>
<li><a href="#JGroups_Subsystem">6. JGroups Subsystem</a>
<ul class="sectlevel2">
<li><a href="#jgroups-purpose">6.1. Purpose</a></li>
<li><a href="#jgroups-configuration-example">6.2. Configuration example</a></li>
<li><a href="#jgroups-use-cases">6.3. Use Cases</a></li>
<li><a href="#discovery-for-kubernetes">6.4. Discovery for Kubernetes</a></li>
</ul>
</li>
<li><a href="#mod_cluster_Subsystem">7. mod_cluster Subsystem</a>
<ul class="sectlevel2">
<li><a href="#configuration">7.1. Configuration</a></li>
<li><a href="#runtime-operations">7.2. Runtime Operations</a></li>
<li><a href="#SSL_Configuration_using_Elytron_Subsystem">7.3. SSL Configuration using Elytron Subsystem</a></li>
</ul>
</li>
<li><a href="#EJB_Services">8. EJB Services</a>
<ul class="sectlevel2">
<li><a href="#ejb-subsystem">8.1. EJB Subsystem</a></li>
<li><a href="#ejb-timer">8.2. EJB Timer</a></li>
</ul>
</li>
<li><a href="#Clustering_API">9. Clustering API</a>
<ul class="sectlevel2">
<li><a href="#group">9.1. Group membership</a></li>
<li><a href="#command-dispatcher">9.2. Command Dispatcher</a></li>
<li><a href="#service-provider-registry">9.3. Service Provider Registry</a></li>
<li><a href="#registry">9.4. Registry</a></li>
</ul>
</li>
<li><a href="#HA_Singleton_Features">10. HA Singleton Features</a></li>
<li><a href="#Singleton_subsystem">11. Singleton subsystem</a>
<ul class="sectlevel2">
<li><a href="#singleton-configuration">11.1. Configuration</a></li>
<li><a href="#non-ha-environments">11.2. Non-HA environments</a></li>
</ul>
</li>
<li><a href="#Singleton_deployments">12. Singleton deployments</a>
<ul class="sectlevel2">
<li><a href="#usage-singleton-deployments">12.1. Usage</a></li>
<li><a href="#singleton-deployment-metrics">12.2. Singleton Deployment metrics</a></li>
</ul>
</li>
<li><a href="#Singleton_MSC_services">13. Singleton MSC services</a>
<ul class="sectlevel2">
<li><a href="#installing-an-msc-service-using-an-existing-singleton-policy">13.1. Installing an MSC service using an existing singleton policy</a></li>
<li><a href="#singleton-msc-service-metrics">13.2. Singleton MSC Service metrics</a></li>
<li><a href="#installing-an-msc-service-using-dynamic-singleton-policy">13.3. Installing an MSC service using dynamic singleton policy</a></li>
</ul>
</li>
<li><a href="#Clustering_and_Domain_Setup_Walkthrough">14. Clustering and Domain Setup Walkthrough</a>
<ul class="sectlevel2">
<li><a href="#preparation-scenario">14.1. Preparation & Scenario</a></li>
<li><a href="#download-wildfly">14.2. Download WildFly</a></li>
<li><a href="#domain-configuration">14.3. Domain Configuration</a></li>
<li><a href="#deployment">14.4. Deployment</a></li>
<li><a href="#cluster-configuration">14.5. Cluster Configuration</a></li>
<li><a href="#testing">14.6. Testing</a></li>
<li><a href="#special-thanks">14.7. Special Thanks</a></li>
</ul>
</li>
</ul>
</div>
</div>
<div id="content">
<div id="preamble">
<div class="sectionbody">
<div class="paragraph">
<p>© 2017 The original authors.</p>
</div>
<!-- toc disabled -->
</div>
</div>
<div class="sect1">
<h2 id="Introduction_To_High_Availability_Services">1. Introduction To High Availability Services</h2>
<div class="sectionbody">
<div class="sect2">
<h3 id="what-are-high-availability-services">1.1. What are High Availability services?</h3>
<div class="paragraph">
<p>WildFly’s High Availability services are used to guarantee availability
of a deployed Jakarta EE application.</p>
</div>
<div class="paragraph">
<p>Deploying critical applications on a single node suffers from two
potential problems:</p>
</div>
<div class="ulist">
<ul>
<li>
<p>loss of application availability when the node hosting the application
crashes (single point of failure)</p>
</li>
<li>
<p>loss of application availability in the form of extreme delays in
response time during high volumes of requests (overwhelmed server)</p>
</li>
</ul>
</div>
<div class="paragraph">
<p>WildFly supports two features which ensure high availability of critical
Jakarta EE applications:</p>
</div>
<div class="ulist">
<ul>
<li>
<p><strong>fail-over:</strong> allows a client interacting with a Jakarta EE application to
have uninterrupted access to that application, even in the presence of
node failures</p>
</li>
<li>
<p><strong>load balancing:</strong> allows a client to have timely responses from the
application, even in the presence of high-volumes of requests</p>
</li>
</ul>
</div>
<div class="admonitionblock important">
<table>
<tr>
<td class="icon">
<i class="fa icon-important" title="Important"></i>
</td>
<td class="content">
These two independent high availability services can very effectively
inter-operate when making use of mod_cluster for load balancing!
</td>
</tr>
</table>
</div>
<div class="paragraph">
<p>Taking advantage of WildFly’s high availability services is easy, and
simply involves deploying WildFly on a cluster of nodes, making a small
number of application configuration changes, and then deploying the
application in the cluster.</p>
</div>
<div class="paragraph">
<p>We now take a brief look at what these services can guarantee.</p>
</div>
</div>
<div class="sect2">
<h3 id="high-availability-through-fail-over">1.2. High Availability through fail-over</h3>
<div class="paragraph">
<p>Fail-over allows a client interacting with a Jakarta EE application to have
uninterrupted access to that application, even in the presence of node
failures. For example, consider a Jakarta EE application which makes use of
the following features:</p>
</div>
<div class="ulist">
<ul>
<li>
<p>session-oriented servlets to provide user interaction</p>
</li>
<li>
<p>session-oriented EJBs to perform state-dependent business computation</p>
</li>
<li>
<p>EJB entity beans to store critical data in a persistent store (e.g.
database)</p>
</li>
<li>
<p>SSO login to the application</p>
</li>
</ul>
</div>
<div class="paragraph">
<p>If the application makes use of WildFly’s fail-over services, a client
interacting with an instance of that application will not be interrupted
even when the node on which that instance executes crashes. Behind the
scenes, WildFly makes sure that all of the user data that the
application make use of (HTTP session data, EJB SFSB sessions, EJB
entities and SSO credentials) are available at other nodes in the
cluster, so that when a failure occurs and the client is redirected to
that new node for continuation of processing (i.e. the client "fails
over" to the new node), the user’s data is available and processing can
continue.</p>
</div>
<div class="paragraph">
<p>The Infinispan and JGroups subsystems are instrumental in providing
these data availability guarantees and will be discussed in detail later
in the guide.</p>
</div>
</div>
<div class="sect2">
<h3 id="high-availability-through-load-balancing">1.3. High Availability through load balancing</h3>
<div class="paragraph">
<p>Load balancing enables the application to respond to client requests in
a timely fashion, even when subjected to a high-volume of requests.
Using a load balancer as a front-end, each incoming HTTP request can be
directed to one node in the cluster for processing. In this way, the
cluster acts as a pool of processing nodes and the load is "balanced"
over the pool, achieving scalability and, as a consequence,
availability. Requests involving session-oriented servlets are directed
to the the same application instance in the pool for efficiency of
processing (sticky sessions). Using mod_cluster has the advantage that
changes in cluster topology (scaling the pool up or down, servers
crashing) are communicated back to the load balancer and used to update
in real time the load balancing activity and avoid requests being
directed to application instances which are no longer available.</p>
</div>
<div class="paragraph">
<p>The mod_cluster subsystem is instrumental in providing support for this
High Availability feature of WildFly and will be discussed in detail
later in this guide.</p>
</div>
</div>
<div class="sect2">
<h3 id="aims-of-the-guide">1.4. Aims of the guide</h3>
<div class="paragraph">
<p>This guide aims to:</p>
</div>
<div class="ulist">
<ul>
<li>
<p>provide a description of the high-availability features available in
WildFly and the services they depend on</p>
</li>
<li>
<p>show how the various high availability services can be configured for
particular application use cases</p>
</li>
<li>
<p>identify default behavior for features relating to
high-availability/clustering</p>
</li>
</ul>
</div>
</div>
<div class="sect2">
<h3 id="organization-of-the-guide">1.5. Organization of the guide</h3>
<div class="paragraph">
<p>As high availability features and their configuration depend on the
particular component they affect (e.g. HTTP sessions, EJB SFSB sessions,
Hibernate), we organize the discussion around those Jakarta EE features. We
strive to make each section as self-contained as possible. Also, when
discussing a feature, we will introduce any WildFly subsystems upon
which the feature depends.</p>
</div>
</div>
</div>
</div>
<div class="sect1">
<h2 id="HTTP_Services">2. HTTP Services</h2>
<div class="sectionbody">
<div class="paragraph">
<p>This section summarizes the HTTP-based clustering features.</p>
</div>
</div>
</div>
<div class="sect1">
<h2 id="Subsystem_Support">3. Subsystem Support</h2>
<div class="sectionbody">
</div>
</div>
<div class="sect1">
<h2 id="Infinispan_Subsystem">4. Infinispan Subsystem</h2>
<div class="sectionbody">
<div class="paragraph">
<p>The Infinispan subsystem configures a set of Infinispan cache containers and cache configurations for use by WildFly clustering services.</p>
</div>
<div class="sect2">
<h3 id="cache-container">4.1. Cache container</h3>
<div class="paragraph">
<p>A cache container manages a set of cache configurations that share the same transport and marshalling configuration.
Cache containers returned by the Infinispan subsystem are auto-configured with the following customizations:</p>
</div>
<div class="ulist">
<ul>
<li>
<p>A custom <a href="#transport">transport</a> capable of sharing a JGroups channel defined by the JGroups subsystem.</p>
</li>
<li>
<p>Uses WildFly’s mbean server, if the org.jboss.as.jmx extension is present.</p>
</li>
<li>
<p>Marshaller configured to resolve classes using JBoss Modules.</p>
</li>
<li>
<p>Marshaller configured with a set of marshalling optimizations for common JDK classes</p>
</li>
<li>
<p>Marshaller configured with additional Externalizers loadable from the configured module attribute.</p>
</li>
</ul>
</div>
<div class="paragraph">
<p>e.g. To create a new cache container that loads marshallers from the "org.bar" module:</p>
</div>
<div class="listingblock">
<div class="content">
<pre class="CodeRay highlight nowrap"><code>/subsystem=infinispan/cache-container=foo:add(module=org.foo)</code></pre>
</div>
</div>
<div class="paragraph">
<p>A cache container may designate a specific cache as its default cache, i.e. the cache returned via <a href="http://docs.jboss.org/infinispan/9.2/apidocs/org/infinispan/manager/CacheContainer.html#getCache--">CacheContainer.getCache()</a>:</p>
</div>
<div class="paragraph">
<p>e.g. To set "bar" as the default cache of the "foo" container:</p>
</div>
<div class="listingblock">
<div class="content">
<pre class="CodeRay highlight nowrap"><code>/subsystem=infinispan/cache-container=foo:write-attribute(name=default-cache, value=bar)</code></pre>
</div>
</div>
<div class="sect3">
<h4 id="transport">4.1.1. Transport</h4>
<div class="paragraph">
<p>Configures the mechanism used by clustered caches to communicate with each other.
It is only necessary to define a transport if the cache container contains clustered caches.</p>
</div>
<div class="paragraph">
<p>To create a JGroups transport using the default channel of the server:</p>
</div>
<div class="listingblock">
<div class="content">
<pre class="CodeRay highlight nowrap"><code>/subsystem=infinispan/cache-container=foo/transport=jgroups:add()</code></pre>
</div>
</div>
<div class="paragraph">
<p>To create a JGroups transport using a distinct "alpha" channel, that uses the "tcp" stack:</p>
</div>
<div class="listingblock">
<div class="content">
<pre class="CodeRay highlight nowrap"><code>/subsystem=jgroups/channel=alpha:add(stack=tcp)
/subsystem=infinispan/cache-container=foo/transport=jgroups:add(channel=alpha)</code></pre>
</div>
</div>
<div class="paragraph">
<p>For a complete list of transport attributes, refer to the <a href="wildscribe" target="_blank" rel="noopener">WildFly management model documentation</a></p>
</div>
<div class="paragraph">
<p>To remove an existing JGroups transport, you can either use the standard remove resource operation:</p>
</div>
<div class="listingblock">
<div class="content">
<pre class="CodeRay highlight nowrap"><code>/subsystem=infinispan/cache-container=foo/transport=jgroups:remove()</code></pre>
</div>
</div>
<div class="paragraph">
<p>…​ or by adding the "none" transport (which will auto-remove any existing transport):</p>
</div>
<div class="listingblock">
<div class="content">
<pre class="CodeRay highlight nowrap"><code>/subsystem=infinispan/cache-container=foo/transport=none:add(){allow-resource-service-restart=true}</code></pre>
</div>
</div>
</div>
<div class="sect3">
<h4 id="cache-types">4.1.2. Cache types</h4>
<div class="paragraph">
<p>Infinispan supports a number of cache types for use in both HA and non-HA server profiles.</p>
</div>
<div class="sect4">
<h5 id="local">Local</h5>
<div class="paragraph">
<p>A local cache stores a given cache entry only on the local node.
A local cache does not require a transport, as cache reads and writes are always local.</p>
</div>
<div class="paragraph">
<p>For more information about this cache type, refer to the <a href="http://infinispan.org/docs/stable/user_guide/user_guide.html#local_mode">the Infinispan documentation</a>.</p>
</div>
<div class="paragraph">
<p>To create a local cache:</p>
</div>
<div class="listingblock">
<div class="content">
<pre class="CodeRay highlight nowrap"><code>/subsystem=infinispan/cache-container=foo/local-cache=bar:add()</code></pre>
</div>
</div>
<div class="paragraph">
<p>For a complete list of local-cache attributes, refer to the <a href="wildscribe" target="_blank" rel="noopener">WildFly management model documentation</a></p>
</div>
</div>
<div class="sect4">
<h5 id="replicated">Replicated</h5>
<div class="paragraph">
<p>A replicated cache stores a given cache entry on every node in the cluster.
A replicated cache requires a transport, as cache writes are replicated to all nodes in the cluster on which the associated cache is running.</p>
</div>
<div class="paragraph">
<p>For more information about this cache type, refer to the <a href="http://infinispan.org/docs/stable/user_guide/user_guide.html#replicated_mode">the Infinispan documentation</a>.</p>
</div>
<div class="paragraph">
<p>To create a replicated cache:</p>
</div>
<div class="listingblock">
<div class="content">
<pre class="CodeRay highlight nowrap"><code>/subsystem=infinispan/cache-container=foo/replicated-cache=bar:add()</code></pre>
</div>
</div>
<div class="paragraph">
<p>For a complete list of replicated-cache attributes, refer to the <a href="wildscribe" target="_blank" rel="noopener">WildFly management model documentation</a></p>
</div>
</div>
<div class="sect4">
<h5 id="distributed">Distributed</h5>
<div class="paragraph">
<p>A distributed cache stores a given cache entry on a configurable number of nodes in the cluster, assigned via an algorithm based on consistent hashing.
A distributed cache requires a transport, as cache writes need to forward to each owner, and cache reads from a non-owner require a remote request.</p>
</div>
<div class="paragraph">
<p>For more information about this cache type, refer to the <a href="http://infinispan.org/docs/stable/user_guide/user_guide.html#distribution_mode">the Infinispan documentation</a>.</p>
</div>
<div class="paragraph">
<p>To create a distributed cache where a given entry is stored on 3 nodes:</p>
</div>
<div class="listingblock">
<div class="content">
<pre class="CodeRay highlight nowrap"><code>/subsystem=infinispan/cache-container=foo/distributed-cache=bar:add(owners=3)</code></pre>
</div>
</div>
<div class="paragraph">
<p>For a complete list of distributed-cache attributes, refer to the <a href="wildscribe" target="_blank" rel="noopener">WildFly management model documentation</a></p>
</div>
</div>
<div class="sect4">
<h5 id="scattered">Scattered</h5>
<div class="paragraph">
<p>A scattered cache is a variation of a distributed cache that maintains 2 copies of a particular cache entry.
Consequently, it can only tolerate failure of a single node at a time.
Primary ownership of a cache entry is determined by the same mechanism used by a distributed cache,
while the backup copy is the node that last updated the entry.</p>
</div>
<div class="paragraph">
<p>This design means that a scattered cache only requires 1 remote invocation to write a given cache entry, regardless of which node initiated the cache operation.
By comparison, a distributed cache (with 2 owners) uses 1 remote invocation to write a cache entry if and only if the primary owner initiated the cache operation, and otherwise requires 2 remote invocations.</p>
</div>
<div class="paragraph">
<p>For more information about this cache type, refer to the <a href="http://infinispan.org/docs/stable/user_guide/user_guide.html#scattered_mode">the Infinispan documentation</a>.</p>
</div>
<div class="paragraph">
<p>To create a scattered cache:</p>
</div>
<div class="listingblock">
<div class="content">
<pre class="CodeRay highlight nowrap"><code>/subsystem=infinispan/cache-container=foo/scattered-cache=bar:add()</code></pre>
</div>
</div>
<div class="paragraph">
<p>For a complete list of scattered-cache attributes, refer to the <a href="wildscribe" target="_blank" rel="noopener">WildFly management model documentation</a></p>
</div>
</div>
<div class="sect4">
<h5 id="invalidation">Invalidation</h5>
<div class="paragraph">