Author: buildbot
Date: Fri Dec 18 16:22:03 2015
New Revision: 975882
Log:
Production update by buildbot for activemq
Modified:
websites/production/activemq/content/cache/main.pageCache
websites/production/activemq/content/failover-transport-reference.html
Modified: websites/production/activemq/content/cache/main.pageCache
==============================================================================
Binary files - no diff available.
Modified: websites/production/activemq/content/failover-transport-reference.html
==============================================================================
--- websites/production/activemq/content/failover-transport-reference.html
(original)
+++ websites/production/activemq/content/failover-transport-reference.html Fri
Dec 18 16:22:03 2015
@@ -35,7 +35,7 @@
<link
href='http://activemq.apache.org/styles/highlighter/styles/shCore.css'
rel='stylesheet' type='text/css' />
<link
href='http://activemq.apache.org/styles/highlighter/styles/shThemeEclipse.css'
rel='stylesheet' type='text/css' />
<script
src='http://activemq.apache.org/styles/highlighter/scripts/shCore.js'
type='text/javascript'></script>
- <script
src='http://activemq.apache.org/styles/highlighter/scripts/shBrushJava.js'
type='text/javascript'></script>
+ <script
src='http://activemq.apache.org/styles/highlighter/scripts/shBrushXml.js'
type='text/javascript'></script>
<script type="text/javascript">
SyntaxHighlighter.defaults['toolbar'] = false;
@@ -81,39 +81,36 @@
<tbody>
<tr>
<td valign="top" width="100%">
-<div class="wiki-content maincontent"><h3
id="FailoverTransportReference-TheFailoverTransport">The Failover
Transport</h3><p>The Failover transport layers reconnect logic on top of any of
the other transports. (We used to call this transport the Reliable transport in
ActiveMQ 3).</p><p>The Failover configuration syntax allows you to specify any
number of composite uris. The Failover transport randomly chooses one of the
composite URI and attempts to establish a connection to it. If it does not
succeed or if it subsequently fails, a new connection is established to one of
the other uris in the list.</p><h4
id="FailoverTransportReference-ConfigurationSyntax">Configuration
Syntax</h4><p><strong>failover:(uri1,...,uriN)?transportOptions</strong><br
clear="none"> or<br clear="none">
<strong>failover:uri1,...,uriN</strong></p><p>The failover transport uses
random by default which lets you to load balance clients over a number of
brokers.</p><p>If you would rather connect to a primary firs
t and only connect to a secondary backup broker if the primary is unavailable,
turn off randomizing using something like</p><div class="preformatted panel"
style="border-width: 1px;"><div class="preformattedContent panelContent">
+<div class="wiki-content maincontent"><h3
id="FailoverTransportReference-TheFailoverTransport">The Failover
Transport</h3><p>The Failover transport layers reconnect logic on top of any of
the other transports. The configuration syntax allows you to specify any number
of composite URIs. The Failover transport randomly chooses one of the composite
URIs and attempts to establish a connection to it. If it does not succeed, or
if it subsequently fails, a new connection is established choosing one of the
other URIs randomly from the list.</p><h4
id="FailoverTransportReference-ConfigurationSyntax">Configuration
Syntax</h4><p><code><strong>failover:(uri1,...,uriN)?transportOptions&nestedOptions</strong></code></p><p>or</p><p><code><strong>failover:uri1,...,uriN</strong></code></p><h5
id="FailoverTransportReference-UsingRandomize">Using Randomize</h5><p>The
Failover transport chooses a URI at <code>random</code> by default. This
effectively load-balances clients over multiple brokers. Ho
wever, to have a client connect to a primary first and only connect to a
secondary backup broker when the primary is unavailable, set
<strong><code>randomize=false</code></strong>. For example:</p><div
class="preformatted panel" style="border-width: 1px;"><div
class="preformattedContent panelContent">
<pre>failover:(tcp://primary:61616,tcp://secondary:61616)?randomize=false
</pre>
-</div></div><h5 id="FailoverTransportReference-TransportOptions">Transport
Options</h5><div class="table-wrap"><table
class="confluenceTable"><tbody><tr><th colspan="1" rowspan="1"
class="confluenceTh"><p>Option Name</p></th><th colspan="1" rowspan="1"
class="confluenceTh"><p>Default Value</p></th><th colspan="1" rowspan="1"
class="confluenceTh"><p>Description</p></th></tr><tr><td colspan="1"
rowspan="1" class="confluenceTd"><p>initialReconnectDelay</p></td><td
colspan="1" rowspan="1" class="confluenceTd"><p>10</p></td><td colspan="1"
rowspan="1" class="confluenceTd"><p>How long to wait before the first reconnect
attempt (in ms)</p></td></tr><tr><td colspan="1" rowspan="1"
class="confluenceTd"><p>maxReconnectDelay</p></td><td colspan="1" rowspan="1"
class="confluenceTd"><p>30000</p></td><td colspan="1" rowspan="1"
class="confluenceTd"><p>The maximum amount of time we ever wait between
reconnect attempts (in ms)</p></td></tr><tr><td colspan="1" rowspan="1"
class="confluenceTd"><p>use
ExponentialBackOff</p></td><td colspan="1" rowspan="1"
class="confluenceTd"><p>true</p></td><td colspan="1" rowspan="1"
class="confluenceTd"><p>Should an exponential backoff be used btween reconnect
attempts</p></td></tr><tr><td colspan="1" rowspan="1"
class="confluenceTd"><p>reconnectDelayExponent</p></td><td colspan="1"
rowspan="1" class="confluenceTd"><p>2.0</p></td><td colspan="1" rowspan="1"
class="confluenceTd"><p>The exponent used in the exponential backoff
attempts</p></td></tr><tr><td colspan="1" rowspan="1"
class="confluenceTd"><p>maxReconnectAttempts</p></td><td colspan="1"
rowspan="1" class="confluenceTd"><p>-1 | 0</p></td><td colspan="1" rowspan="1"
class="confluenceTd"><p>From version 5.6 onwards: -1 is default and means retry
forever, 0 means don't retry (only try connection once but no retry). <br
clear="none" class="atl-forced-newline"> Prior to version 5.6: 0 is default and
means retry forever. <br clear="none" class="atl-forced-newline"> All versions:
If set to &g
t;0, then this is the maximum number of reconnect attempts before an error is
sent back to the client.</p></td></tr><tr><td colspan="1" rowspan="1"
class="confluenceTd"><p>startupMaxReconnectAttempts</p></td><td colspan="1"
rowspan="1" class="confluenceTd"><p>-1</p></td><td colspan="1" rowspan="1"
class="confluenceTd"><p>If not 0, then this is the maximum number of reconnect
attempts before an error is sent back to the client on the first attempt by the
client to start a connection, once connected the
<strong>maxReconnectAttempts</strong> option takes precedence.  A value of
-1 signifies that the transport will have no limit to the number of initial
connection attempts.</p></td></tr><tr><td colspan="1" rowspan="1"
class="confluenceTd"><p>randomize</p></td><td colspan="1" rowspan="1"
class="confluenceTd"><p>true</p></td><td colspan="1" rowspan="1"
class="confluenceTd"><p>use a random algorithm to choose the the URI to use for
reconnect from the list provided</p></td></tr><tr><td
colspan="1" rowspan="1" class="confluenceTd"><p>backup</p></td><td
colspan="1" rowspan="1" class="confluenceTd"><p>false</p></td><td colspan="1"
rowspan="1" class="confluenceTd"><p>initialize and hold a second transport
connection - to enable fast failover</p></td></tr><tr><td colspan="1"
rowspan="1" class="confluenceTd"><p>timeout</p></td><td colspan="1" rowspan="1"
class="confluenceTd"><p>-1</p></td><td colspan="1" rowspan="1"
class="confluenceTd"><p>Enables timeout on send operations (in miliseconds)
without interruption of reconnection process</p></td></tr><tr><td colspan="1"
rowspan="1" class="confluenceTd"><p>trackMessages</p></td><td colspan="1"
rowspan="1" class="confluenceTd"><p>false</p></td><td colspan="1" rowspan="1"
class="confluenceTd"><p>keep a cache of in-flight messages that will flushed to
a broker on reconnect</p></td></tr><tr><td colspan="1" rowspan="1"
class="confluenceTd"><p>maxCacheSize</p></td><td colspan="1" rowspan="1"
class="confluenceTd"><p>131072</p></t
d><td colspan="1" rowspan="1" class="confluenceTd"><p>size in bytes for the
cache, if trackMessages is enabled</p></td></tr><tr><td colspan="1" rowspan="1"
class="confluenceTd"><p>updateURIsSupported</p></td><td colspan="1" rowspan="1"
class="confluenceTd"><p>true</p></td><td colspan="1" rowspan="1"
class="confluenceTd"><p>Determines whether the client should accept updates to
its list of known URIs from the connected broker. <strong>Added in ActiveMQ
5.4</strong></p></td></tr><tr><td colspan="1" rowspan="1"
class="confluenceTd"><p>updateURIsURL</p></td><td colspan="1" rowspan="1"
class="confluenceTd"><p>null</p></td><td colspan="1" rowspan="1"
class="confluenceTd"><p>A URL (or path to a local file) to a text file
containing a comma separated list of URIs to use for reconnect in the case of
failure. <strong>Added in ActiveMQ 5.4</strong></p></td></tr><tr><td
colspan="1" rowspan="1" class="confluenceTd"><p>nested.*</p></td><td
colspan="1" rowspan="1" class="confluenceTd"><p>null</p><
/td><td colspan="1" rowspan="1" class="confluenceTd"><p>Extra options to add
to the nested URLs. <strong>Added in ActiveMQ 5.9</strong></p></td></tr><tr><td
colspan="1" rowspan="1"
class="confluenceTd"><p>warnAfterReconnectAttempts</p></td><td colspan="1"
rowspan="1" class="confluenceTd"><p>10</p></td><td colspan="1" rowspan="1"
class="confluenceTd"><p>After every N reconnect attempts log a warning to
indicate there is no connection but that we are still trying, set to <= 0 to
disable. <strong>Added in ActiveMQ 5.10</strong></p></td></tr><tr><td
colspan="1" rowspan="1" class="confluenceTd">reconnectSupported</td><td
colspan="1" rowspan="1" class="confluenceTd">true</td><td colspan="1"
rowspan="1" class="confluenceTd">Determines whether the client should respond
to broker ConnectionControl events with a reconnect (see:
<span>rebalanceClusterClients)</span></td></tr></tbody></table></div><h5
id="FailoverTransportReference-ExampleURI">Example URI</h5><div
class="preformatted panel"
style="border-width: 1px;"><div class="preformattedContent panelContent">
+</div></div><h5 id="FailoverTransportReference-TransportOptions">Transport
Options</h5><div class="table-wrap"><table
class="confluenceTable"><tbody><tr><th colspan="1" rowspan="1"
class="confluenceTh"><p>Option Name</p></th><th colspan="1" rowspan="1"
class="confluenceTh"><p>Default Value</p></th><th colspan="1" rowspan="1"
class="confluenceTh"><p>Description</p></th></tr><tr><td colspan="1"
rowspan="1"
class="confluenceTd"><p><code>initialReconnectDelay</code></p></td><td
colspan="1" rowspan="1" class="confluenceTd"><p><code>10</code></p></td><td
colspan="1" rowspan="1" class="confluenceTd"><p>The delay (in ms) before the
<em>first</em> reconnect attempt.</p></td></tr><tr><td colspan="1" rowspan="1"
class="confluenceTd"><p><code>maxReconnectDelay</code></p></td><td colspan="1"
rowspan="1" class="confluenceTd"><p><code>30000</code></p></td><td colspan="1"
rowspan="1" class="confluenceTd"><p>The maximum delay (in ms) between the
<em>second and subsequent</em> reconnect attempts.</p>
</td></tr><tr><td colspan="1" rowspan="1"
class="confluenceTd"><p><code>useExponentialBackOff</code></p></td><td
colspan="1" rowspan="1" class="confluenceTd"><p><code>true</code></p></td><td
colspan="1" rowspan="1" class="confluenceTd"><p>If
<strong><code>true</code></strong> an exponential back-off is used between
reconnect attempts.</p></td></tr><tr><td colspan="1" rowspan="1"
class="confluenceTd"><p><code>reconnectDelayExponent</code></p></td><td
colspan="1" rowspan="1" class="confluenceTd"><p><code>2.0</code></p></td><td
colspan="1" rowspan="1" class="confluenceTd"><p>The exponent used during
exponential back-off attempts.</p></td></tr><tr><td colspan="1" rowspan="1"
class="confluenceTd"><p><code>maxReconnectAttempts</code></p></td><td
colspan="1" rowspan="1" class="confluenceTd"><p><code>-1 | 0</code></p></td><td
colspan="1" rowspan="1" class="confluenceTd"><p><em>From</em> ActiveMQ 5.6:
default is <strong><code>-1</code></strong>, retry forever.
<strong><code>0</code></strong>
means disables re-connection, e.g: just try to connect once.<br clear="none"
class="atl-forced-newline"> <em>Before</em> ActiveMQ 5.6: default is
<strong><code>0</code></strong>, retry forever. <br clear="none"
class="atl-forced-newline"> <em>All versions</em>: a value
<strong><code>>0</code></strong> denotes the maximum number of reconnect
attempts before an error is sent back to the client.</p></td></tr><tr><td
colspan="1" rowspan="1"
class="confluenceTd"><p><code>startupMaxReconnectAttempts</code></p></td><td
colspan="1" rowspan="1" class="confluenceTd"><p><code>-1</code></p></td><td
colspan="1" rowspan="1" class="confluenceTd"><p>If not
<strong><code>0</code></strong>, then this is the maximum number of reconnect
attempts before an error is sent back to the client on the first attempt by the
client to start a connection. Once connected, however, the
<code><strong>maxReconnectAttempts</strong></code> option then
applies. </p><p>A value of <strong><code>-1</code></strong>
signifies that the transport will have no limit to the number of initial
connection attempts.</p></td></tr><tr><td colspan="1" rowspan="1"
class="confluenceTd"><p><code>randomize</code></p></td><td colspan="1"
rowspan="1" class="confluenceTd"><p><code>true</code></p></td><td colspan="1"
rowspan="1" class="confluenceTd"><p>If <strong><code>true</code></strong>,
choose a URI at random from the list to use for reconnect.</p></td></tr><tr><td
colspan="1" rowspan="1" class="confluenceTd"><p><code>backup</code></p></td><td
colspan="1" rowspan="1" class="confluenceTd"><p><code>false</code></p></td><td
colspan="1" rowspan="1" class="confluenceTd"><p>Initialize and hold a second
transport connection - to enable fast failover.</p></td></tr><tr><td
colspan="1" rowspan="1"
class="confluenceTd"><p><code>timeout</code></p></td><td colspan="1"
rowspan="1" class="confluenceTd"><p><code>-1</code></p></td><td colspan="1"
rowspan="1" class="confluenceTd"><p>Set the timeout on send operations (in ms)
without interruption of re-connection process. <strong>Since ActiveMQ
5.3</strong>.</p></td></tr><tr><td colspan="1" rowspan="1"
class="confluenceTd"><p><code>trackMessages</code></p></td><td colspan="1"
rowspan="1" class="confluenceTd"><p><code>false</code></p></td><td colspan="1"
rowspan="1" class="confluenceTd"><p>Keep a cache of in-flight messages that
will flushed to a broker on reconnect.</p></td></tr><tr><td colspan="1"
rowspan="1" class="confluenceTd"><p><code>maxCacheSize</code></p></td><td
colspan="1" rowspan="1" class="confluenceTd"><p><code>131072</code></p></td><td
colspan="1" rowspan="1" class="confluenceTd"><p>Size in bytes for the cache of
tracked messages. Applicable only if
<strong><code>trackMessages</code></strong> is
<strong><code>true</code></strong>.</p></td></tr><tr><td colspan="1"
rowspan="1"
class="confluenceTd"><p><code>updateURIsSupported</code></p></td><td
colspan="1" rowspan="1" class="confluenceTd"><p><code>true</code></p></td><td
colspan="1" rowspan="
1" class="confluenceTd"><p>Determines whether the client should accept updates
from the broker to its list of known URIs. <strong>Since</strong><strong>
ActiveMQ 5.4.</strong></p></td></tr><tr><td colspan="1" rowspan="1"
class="confluenceTd"><p><code>updateURIsURL</code></p></td><td colspan="1"
rowspan="1" class="confluenceTd"><p><code>null</code></p></td><td colspan="1"
rowspan="1" class="confluenceTd"><p>A URL (or path to a local file) to a text
file containing a comma separated list of URIs to use for reconnect in the case
of failure. <strong>Since ActiveMQ 5.4.</strong></p></td></tr><tr><td
colspan="1" rowspan="1"
class="confluenceTd"><p><code>nested.*</code></p></td><td colspan="1"
rowspan="1" class="confluenceTd"><p><code>null</code></p></td><td colspan="1"
rowspan="1" class="confluenceTd"><p>Extra options to add to the nested URLs.
<strong>Since ActiveMQ 5.9.</strong></p></td></tr><tr><td colspan="1"
rowspan="1" class="confluenceTd"><p><code>warnAfterReconnectAttempts</c
ode></p></td><td colspan="1" rowspan="1"
class="confluenceTd"><p><code>10</code></p></td><td colspan="1" rowspan="1"
class="confluenceTd"><p>Log a warning after every N reconnect attempts. This
indicates that there is no current connection but re-connection is being
attempted. Set to <strong><code><= 0</code></strong> to disable.
<strong>Since ActiveMQ 5.10.</strong></p></td></tr><tr><td colspan="1"
rowspan="1" class="confluenceTd"><code>reconnectSupported</code></td><td
colspan="1" rowspan="1" class="confluenceTd"><code>true</code></td><td
colspan="1" rowspan="1" class="confluenceTd"><p>Determines whether the client
should respond to broker <strong><code>ConnectionControl</code></strong> events
with a reconnect (see:
<strong><code>rebalanceClusterClients</code>).</strong></p></td></tr></tbody></table></div><h5
id="FailoverTransportReference-ExampleURI">Example URI</h5><div
class="preformatted panel" style="border-width: 1px;"><div
class="preformattedContent panelContent">
<pre>failover:(tcp://localhost:61616,tcp://remotehost:61616)?initialReconnectDelay=100
</pre>
-</div></div><p>If the above gives errors try it this way (this way works in
ActiveMQ 4.1.1 the one above does not)</p><div class="preformatted panel"
style="border-width: 1px;"><div class="preformattedContent panelContent">
-<pre>failover://(tcp://localhost:61616,tcp://remotehost:61616)?initialReconnectDelay=100
-</pre>
-</div></div><h5 id="FailoverTransportReference-Notes">Notes</h5><p>If you use
failover, and a broker dies at some point, your sends will block by default.
Using <a shape="rect" class="external-link"
href="http://activemq.apache.org/maven/5.5.0/activemq-core/apidocs/org/apache/activemq/transport/TransportListener.html";>TransportListener</a>
can help with this regard. It is best to set the Listener directly on the <a
shape="rect" class="external-link"
href="http://activemq.apache.org/maven/5.5.0/activemq-core/apidocs/org/apache/activemq/ActiveMQConnectionFactory.html#setTransportListener(org.apache.activemq.transport.TransportListener)">ActiveMQConnectionFactory</a>
so that it is in place before any request that may require an network hop.<br
clear="none"> Additionally you can use <em>timeout</em> option which will cause
your current send to fail after specified timeout. The following URL, for
example</p><div class="preformatted panel" style="border-width: 1px;"><div
class="preformatt
edContent panelContent">
+</div></div><h5 id="FailoverTransportReference-Notes">Notes</h5><p>Under the
Failover transport send operations will, by default, block indefinitely when
the broker becomes unavailable. There are two options available for handling
this scenario. First, either set a <a shape="rect" class="external-link"
href="http://activemq.apache.org/maven/5.5.0/activemq-core/apidocs/org/apache/activemq/transport/TransportListener.html";>TransportListener</a>
directly on the <a shape="rect" class="external-link"
href="http://activemq.apache.org/maven/5.5.0/activemq-core/apidocs/org/apache/activemq/ActiveMQConnectionFactory.html#setTransportListener(org.apache.activemq.transport.TransportListener)">ActiveMQConnectionFactory</a>,
so that it is in place before any request that may require a network hop or
second, set the <strong><code>timeout</code></strong> option. The
<strong><code>timeout</code></strong> option causes the current send operation
to fail after the specified timeout. For example:</p><d
iv class="preformatted panel" style="border-width: 1px;"><div
class="preformattedContent panelContent">
<pre>failover:(tcp://primary:61616)?timeout=3000
</pre>
-</div></div><p>will cause send to fail after 3 seconds if the connection isn't
established. The connection will not be killed, so you can try sending messages
later at some point using the same connection (presumably some of your brokers
will be available again). Timeouts on the failover transport are available
since 5.3 version.</p><h5
id="FailoverTransportReference-Transactions">Transactions</h5><p>The Failover
transport tracks transactions by default. The inflight transactions are
replayed on reconnection. For simple scenarios this works ok. However there is
an assumption for acknowledged (or consumer) transactions, that the previously
received messages will get relayed after a reconnect. This is not always true
when there are many connections and consumers, as redelivery order is not
guaranteed. It is possible to have stale outstanding acknowledgements that can
interfere with newly delivered messages, potentially leading to unacknowledged
messages.<br clear="none"> Starting in v
ersion 5.3.1, redelivery order is tracked and a transaction will fail to
commit (throw a TransactionRolledBackException) if outstanding messages are not
redelivered after failover. In addition, in doubt transaction will now result
in a rollback such that they can be replayed by the application. In doubt
transactions occur when failover happens with a commit message inflight. It is
not possible to know the exact point of failure. Did the transaction commit
message get delivered or was it just the commit reply that is lost? In this
case, it is necessary to rollback so that the application can get an indication
of the failure and deal with any potential problem.</p><h5
id="FailoverTransportReference-BrokersideOptionsforFailover">Broker side
Options for Failover</h5><p><span style="color: red;"><strong><em>This is new
in version 5.4:</em></strong></span></p><p>There are some options that are
available on a TransportConnector that is used by the broker that can be used
to update clients
automatically with information about new brokers to failover to. These
are:</p><div class="table-wrap"><table class="confluenceTable"><tbody><tr><th
colspan="1" rowspan="1" class="confluenceTh"><p>Option Name</p></th><th
colspan="1" rowspan="1" class="confluenceTh"><p>Default Value</p></th><th
colspan="1" rowspan="1"
class="confluenceTh"><p>Description</p></th></tr><tr><td colspan="1"
rowspan="1" class="confluenceTd"><p>updateClusterClients</p></td><td
colspan="1" rowspan="1" class="confluenceTd"><p>false</p></td><td colspan="1"
rowspan="1" class="confluenceTd"><p>if true, pass information to connected
clients about changes in the topology of the broker
cluster</p></td></tr><tr><td colspan="1" rowspan="1"
class="confluenceTd"><p>rebalanceClusterClients</p></td><td colspan="1"
rowspan="1" class="confluenceTd"><p>false</p></td><td colspan="1" rowspan="1"
class="confluenceTd"><p>if true, connected clients will be asked to rebalance
across a cluster of brokers when a new broker joins th
e network of brokers (note: priorityBackup=true can
override)</p></td></tr><tr><td colspan="1" rowspan="1"
class="confluenceTd"><p>updateClusterClientsOnRemove</p></td><td colspan="1"
rowspan="1" class="confluenceTd"><p>false</p></td><td colspan="1" rowspan="1"
class="confluenceTd"><p>if true, will update clients when a cluster is removed
from the network. Having this as separate option enables clients to be updated
when new brokers join, but not when brokers leave.</p></td></tr><tr><td
colspan="1" rowspan="1" class="confluenceTd"><p>updateClusterFilter</p></td><td
colspan="1" rowspan="1" class="confluenceTd"><p>null</p></td><td colspan="1"
rowspan="1" class="confluenceTd"><p>comma separated list of regular expression
filters used to match broker names of brokers to designate as being part of the
failover cluster for the clients</p></td></tr></tbody></table></div><p>An
example as defined within the broker's XML configuration file:</p><div
class="code panel pdl" style="border-width:
1px;"><div class="codeContent panelContent pdl">
-<pre class="brush: java; gutter: false; theme: Default"
style="font-size:12px;"><broker>
+</div></div><p>In this example if the connection isn't established the send
operation will timeout after 3 seconds. It is important to note that the
connection <em>is not killed</em> when a timeout occurs. It is possible,
therefore, to resend the affected message(s) later using the <em>same</em>
connection once a broker becomes available.</p><h5
id="FailoverTransportReference-Transactions">Transactions</h5><p>The Failover
transport tracks transactions by default. In-flight transactions are replayed
upon re-connection. For simple scenarios this works as expected. However, there
is an assumption regarding acknowledged (or consumer) transactions in that the
previously received messages will automatically be replayed upon re-connection.
This, however, is not always true when there are many connections and
consumers, as re-delivery order is not guaranteed as stale outstanding
acknowledgements can interfere with newly delivered messages. This can lead to
unacknowledged messages.</p><p>Sta
rting in version 5.3.1, however, re-delivery order <em>is</em> tracked and a
transaction will fail to commit if outstanding messages are not redelivered
after failover. A
<strong><code>javax.jms.</code><code>TransactionRolledBackException</code></strong>
is thrown if the commit fails. In doubt transactions will result in a rollback
such that they can be replayed by the application. In doubt transactions occur
when failover happens when a commit message is in-flight. It is not possible to
know the exact point of failure. Did failure happen because the transaction
commit message was not delivered or was the commit reply lost? In either case,
it becomes necessary to rollback the transaction so that the application can
get an indication of the failure and deal with any potential problem.</p><h5
id="FailoverTransportReference-Broker-sideOptionsforFailover">Broker-side
Options for Failover</h5><p><span style="color: red;"><strong><em>This is new
in version 5.4:</em></strong></span></p><p>
The TransportConnector has options available so that the broker can update
clients automatically regarding information of about the presence new brokers
available for failover. The options are:</p><div class="table-wrap"><table
class="confluenceTable"><tbody><tr><th colspan="1" rowspan="1"
class="confluenceTh"><p>Option Name</p></th><th colspan="1" rowspan="1"
class="confluenceTh"><p>Default Value</p></th><th colspan="1" rowspan="1"
class="confluenceTh"><p>Description</p></th></tr><tr><td colspan="1"
rowspan="1"
class="confluenceTd"><p><code>updateClusterClients</code></p></td><td
colspan="1" rowspan="1" class="confluenceTd"><p><code>false</code></p></td><td
colspan="1" rowspan="1"
class="confluenceTd"><p>If <strong><code>true</code></strong>, pass
information to connected clients about changes in the topology of the broker
cluster.</p></td></tr><tr><td colspan="1" rowspan="1"
class="confluenceTd"><p><code>rebalanceClusterClients</code></p></td><td
colspan="1" rowspan="1" class
="confluenceTd"><p><code>false</code></p></td><td colspan="1" rowspan="1"
class="confluenceTd"><p>If <strong><code>true</code></strong>, connected
clients will be asked to re-balance across a cluster of brokers when a new
broker joins the network of brokers
(note: <strong><code>priorityBackup=true</code></strong> can
override).</p></td></tr><tr><td colspan="1" rowspan="1"
class="confluenceTd"><p><code>updateClusterClientsOnRemove</code></p></td><td
colspan="1" rowspan="1" class="confluenceTd"><p>false</p></td><td colspan="1"
rowspan="1" class="confluenceTd"><p>If <strong><code>true</code></strong>, will
update clients when a cluster is removed from the network. Having this as
separate option enables clients to be updated when new brokers join, but
<em>not</em> when brokers leave.</p></td></tr><tr><td colspan="1" rowspan="1"
class="confluenceTd"><p><code>updateClusterFilter</code></p></td><td
colspan="1" rowspan="1" class="confluenceTd"><p><code>null</code></p></td><td
colspan="
1" rowspan="1" class="confluenceTd"><p>Comma separated list of regular
expression filters used to match broker names of brokers to designate as being
part of the failover cluster for the
clients.</p></td></tr></tbody></table></div><p>For example:</p><div class="code
panel pdl" style="border-width: 1px;"><div class="codeContent panelContent pdl">
+<pre class="brush: xml; gutter: false; theme: Confluence"
style="font-size:12px;"><broker>
...
<transportConnectors>
- <transportConnector name="openwire" uri="tcp://0.0.0.0:61616"
updateClusterClients="true" updateClusterFilter=".*A.*,.*B.*" />
+ <transportConnector name="openwire" uri="tcp://0.0.0.0:61616"
updateClusterClients="true" updateClusterFilter=".*A.*,.*B.*"/>
</<transportConnectors>
...
</broker>
</pre>
-</div></div><p>If updateClusterClients is enabled, then your clients will only
need to know about the first broker to connect to in a cluster of brokers -
e.g.:</p><div class="preformatted panel" style="border-width: 1px;"><div
class="preformattedContent panelContent">
-<pre>failover://tcp://primary:61616
+</div></div><p>If <strong><code>updateClusterClients=true</code></strong>,
then clients only need to be configured with the details of one broker within a
cluster to connect to. For example:</p><div class="preformatted panel"
style="border-width: 1px;"><div class="preformattedContent panelContent">
+<pre>failover:(tcp://primary:61616)
</pre>
-</div></div><p>If new brokers join, the client will automatically be updated
with the additional URI of that broker to connect to in the event of a network
or broker failure.</p><h6 id="FailoverTransportReference-MoreInformation">More
Information</h6><p>Also check out the following blog entry about using the
cluster client updates and rebalancing features titled <a shape="rect"
class="external-link"
href="http://bsnyderblog.blogspot.com/2010/10/new-features-in-activemq-54-automatic.html";
rel="nofollow">New Features in ActiveMQ 5.4: Automatic Cluster Update and
Rebalance</a>.</p><h5 id="FailoverTransportReference-PriorityBackup">Priority
Backup</h5><p>If your setup have brokers in both local and remote networks, you
probably want your clients connected to the local ones if those are available.
As of version 5.6, ActiveMQ supports priority backup feature, so you can have
your clients automatically reconnect to so called priority (or local) urls.
Consider the following url</p><div clas
s="code panel pdl" style="border-width: 1px;"><div class="codeContent
panelContent pdl">
-<pre class="brush: java; gutter: false; theme: Default"
style="font-size:12px;">failover:(tcp://local:61616,tcp://remote:61616)?randomize=false&priorityBackup=true</pre>
-</div></div><p>If this url is used for the client, the client will try to
connect and stay connected to the <code>local</code> broker. If local broker
fails, it will of course fail over to the remote one. But as
<code>priorityBackup</code> parameter is used, it will constantly try to
reconnect to the local broker. Once it can do so, the client will get back to
it without any need for manual intervention.</p><p>By default, only the first
url in the list is considered prioritized (local). In most cases this will
suffice, but in some cases you can have multiple "local" urls. You can
configure which urls are considered prioritized, by using
<code>priorityURIs</code> parameter, like</p><div class="code panel pdl"
style="border-width: 1px;"><div class="codeContent panelContent pdl">
-<pre class="brush: java; gutter: false; theme: Default"
style="font-size:12px;">failover:(tcp://local1:61616,tcp://local2:61616,tcp://remote:61616)?randomize=false&priorityBackup=true&priorityURIs=tcp://local1:61616,tcp://local2:61616</pre>
-</div></div><p>In this case the client will prioritize either
<code>local1</code> or <code>local2</code> brokers and (re)connect to them if
they are available.</p><h5
id="FailoverTransportReference-PassingextraoptionstothenestedURLs.">Passing
extra options to the nested URLs.</h5><p><span style="color:
red;"><strong><em>This is new in version 5.9:</em></strong></span><br
clear="none"> You can now add options the nested URLs via options on the
failover URL. Previously, if you wanted to detect dead connections faster you
had to add the wireFormat.maxInactivityDuration=1000 option to all the nested
URLs in the failover list. For example:</p><div class="code panel pdl"
style="border-width: 1px;"><div class="codeContent panelContent pdl">
-<pre class="brush: java; gutter: false; theme: Default"
style="font-size:12px;">failover:(tcp://host01:61616?wireFormat.maxInactivityDuration=1000,tcp://host02:61616?wireFormat.maxInactivityDuration=1000,tcp://host03:61616?wireFormat.maxInactivityDuration=1000)</pre>
-</div></div><p>As of ActiveMQ 5.9, you can now do the same thing using the
following URL:</p><div class="code panel pdl" style="border-width: 1px;"><div
class="codeContent panelContent pdl">
-<pre class="brush: java; gutter: false; theme: Default"
style="font-size:12px;">failover:(tcp://host01:61616,tcp://host02:61616,tcp://host03:61616)?nested.wireFormat.maxInactivityDuration=1000</pre>
-</div></div></div>
+</div></div><p>when new brokers join the cluster the client is automatically
informed of the new broker's URI. The new URI is then available for failover
when one of the other known brokers becomes unavailable.</p><h6
id="FailoverTransportReference-MoreInformation">More Information</h6><p>Also
check out the following blog entry about using the cluster client updates and
re-balancing features titled <a shape="rect" class="external-link"
href="http://bsnyderblog.blogspot.com/2010/10/new-features-in-activemq-54-automatic.html";
rel="nofollow">New Features in ActiveMQ 5.4: Automatic Cluster Update and
Rebalance</a>.</p><h5 id="FailoverTransportReference-PriorityBackup">Priority
Backup</h5><p>If brokers are available in both local and remote networks, it's
possible to specify a preference for local brokers over remote brokers using
the <strong><code>priorityBackup</code></strong> and
<strong><code>priorityURIs</code></strong> options (since ActiveMQ 5.6).
Consider the following URL:</p><d
iv class="preformatted panel" style="border-width: 1px;"><div
class="preformattedContent panelContent">
+<pre>failover:(tcp://local:61616,tcp://remote:61616)?randomize=false&priorityBackup=true</pre>
+</div></div><p>Given this URL the client will try to connect and stay
connected to the <strong><code>local</code></strong> broker. If
<strong><code>local</code></strong> broker fails, it will of course fail over
to <strong><code>remote</code></strong>. However, as
<strong><code>priorityBackup</code></strong> parameter is used, the client will
constantly try to reconnect to <strong><code> local</code></strong>. Once the
client can do so, the client will re-connect to it without any need for manual
intervention.</p><p>By default, only the first URI in the list is considered
prioritized (local). In most cases this will suffice, but in some cases you can
have multiple "local" URIs. The <strong><code>priorityURIs</code></strong>
option can be used to specify which URIs are considered prioritized. For
example:</p><div class="preformatted panel" style="border-width: 1px;"><div
class="preformattedContent panelContent">
+<pre>failover:(tcp://local1:61616,tcp://local2:61616,tcp://remote:61616)?randomize=false&priorityBackup=true&priorityURIs=tcp://local1:61616,tcp://local2:61616</pre>
+</div></div><p>In this case the client will prioritize either
<strong><code>local1</code></strong> or <strong><code>local2</code></strong>
brokers and (re-)connect to them if they are available.</p><h5
id="FailoverTransportReference-ConfiguringNestedURIOptions.">Configuring Nested
URI Options.</h5><p><span style="color: rgb(255,0,0);">As of ActiveMQ
5.9</span> it's possible to specify common URI options by appending them to the
query string of failover URI itself. Common URI options must be prefixed with
<strong><code>'nested.'</code></strong>.  Note that if the same option is
specified as both an individual URI option <em>and</em> a nested option, the
nested option definition takes precedence.</p><p>For example, instead of doing
this:</p><div class="preformatted panel" style="border-width: 1px;"><div
class="preformattedContent panelContent">
+<pre>failover:(tcp://broker1:61616?wireFormat.maxInactivityDuration=1000,tcp://broker2:61616?wireFormat.maxInactivityDuration=1000,tcp://broker3:61616?wireFormat.maxInactivityDuration=1000)
</pre>
+</div></div><p>do this:</p><div class="preformatted panel"
style="border-width: 1px;"><div class="preformattedContent panelContent">
+<pre>failover:(tcp://broker1:61616,tcp://broker2:61616,tcp://broker3:61616)?nested.wireFormat.maxInactivityDuration=1000</pre>
+</div></div><p>Any option that can applied to the query string of the
individual URIs is a candidate for use with the
<strong><code>nested</code></strong> option.</p><p> </p><p> </p></div>
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