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Posted to commits@zookeeper.apache.org by rg...@apache.org on 2015/11/09 00:26:15 UTC
svn commit: r1713322 - in /zookeeper/branches/branch-3.4: CHANGES.txt
docs/zookeeperAdmin.html docs/zookeeperStarted.html
Author: rgs
Date: Sun Nov 8 23:26:15 2015
New Revision: 1713322
URL: http://svn.apache.org/viewvc?rev=1713322&view=rev
Log:
ZOOKEEPER-2240: Make the three-node minimum more explicit in documentation
and on website (Shawn Heisey via rgs)
Modified:
zookeeper/branches/branch-3.4/CHANGES.txt
zookeeper/branches/branch-3.4/docs/zookeeperAdmin.html
zookeeper/branches/branch-3.4/docs/zookeeperStarted.html
Modified: zookeeper/branches/branch-3.4/CHANGES.txt
URL: http://svn.apache.org/viewvc/zookeeper/branches/branch-3.4/CHANGES.txt?rev=1713322&r1=1713321&r2=1713322&view=diff
==============================================================================
--- zookeeper/branches/branch-3.4/CHANGES.txt (original)
+++ zookeeper/branches/branch-3.4/CHANGES.txt Sun Nov 8 23:26:15 2015
@@ -185,6 +185,9 @@ IMPROVEMENTS:
ZOOKEEPER-2315: Change client connect zk service timeout log level from Info
to Warn level (Lin Yiqun via rgs)
+ ZOOKEEPER-2240: Make the three-node minimum more explicit in documentation
+ and on website (Shawn Heisey via rgs)
+
NEW FEATURES:
ZOOKEEPER-2237 Port async multi to 3.4 branch (Ivan Kelly via rakeshr)
Modified: zookeeper/branches/branch-3.4/docs/zookeeperAdmin.html
URL: http://svn.apache.org/viewvc/zookeeper/branches/branch-3.4/docs/zookeeperAdmin.html?rev=1713322&r1=1713321&r2=1713322&view=diff
==============================================================================
--- zookeeper/branches/branch-3.4/docs/zookeeperAdmin.html (original)
+++ zookeeper/branches/branch-3.4/docs/zookeeperAdmin.html Sun Nov 8 23:26:15 2015
@@ -437,6 +437,27 @@ document.write("Last Published: " + docu
only handle the failure of a single machine; if two machines fail, the
remaining two machines do not constitute a majority. However, with five
machines ZooKeeper can handle the failure of two machines. </p>
+
+<div class="note">
+<div class="label">Note</div>
+<div class="content">
+<p>As mentioned in the Getting Started guide, a minimum of three servers are
+ required for a fault tolerant clustered setup, and it is strongly
+ recommended that you have an odd number of servers.</p>
+<p>Usually three servers is more than enough for a production install, but
+ for maximum reliability during maintenance, you may wish to install
+ five servers. With three servers, if you perform maintenance on
+ one of them, you are vulnerable to a failure on one of the other
+ two servers during that maintenance. If you have five of them
+ running, you can take one down for maintenance, and know that
+ you're still OK if one of the other four suddenly fails.</p>
+<p>Your redundancy considerations should include all aspects of your
+ environment. If you have three zookeeper servers, but their
+ network cables are all plugged into the same network switch, then
+ the failure of that switch will take down your entire ensemble.</p>
+</div>
+</div>
+
<p>Here are the steps to setting a server that will be part of an
ensemble. These steps should be performed on every host in the
ensemble:</p>
Modified: zookeeper/branches/branch-3.4/docs/zookeeperStarted.html
URL: http://svn.apache.org/viewvc/zookeeper/branches/branch-3.4/docs/zookeeperStarted.html?rev=1713322&r1=1713321&r2=1713322&view=diff
==============================================================================
--- zookeeper/branches/branch-3.4/docs/zookeeperStarted.html (original)
+++ zookeeper/branches/branch-3.4/docs/zookeeperStarted.html Sun Nov 8 23:26:15 2015
@@ -533,8 +533,23 @@ numChildren = 0
ZooKeeper in replicated mode. A replicated group of servers in the same
application is called a <em>quorum</em>, and in replicated
mode, all servers in the quorum have copies of the same configuration
- file. The file is similar to the one used in standalone mode, but with a
- few differences. Here is an example:</p>
+ file.</p>
+
+<div class="note">
+<div class="label">Note</div>
+<div class="content">
+<p>For replicated mode, a minimum of three servers are required, and it is
+ strongly recommended that you have an odd number of servers. If you
+ only have two servers, then you are in a situation where if one of
+ them fails, there are not enough machines to form a majority quorum.
+ Two servers is inherently <strong>less</strong> stable than a single
+ server, because there are two single points of failure.</p>
+</div>
+</div>
+
+<p>The required <strong>conf/zoo.cfg</strong> file for replicated mode is
+ similar to the one used in standalone mode, but with a few differences.
+ Here is an example:</p>
<pre class="code">
tickTime=2000
dataDir=/var/lib/zookeeper
@@ -583,7 +598,15 @@ server.3=zoo3:2888:3888
(in the above replicated example, running on a
single <em>localhost</em>, you would still have
three config files).</p>
-
+
+<p>Please be aware that setting up multiple servers on a single machine
+ will not create any redundancy. If something were to happen
+ which caused the machine to die, all of the zookeeper servers
+ would be offline. Full redundancy requires that each server have
+ its own machine. It must be a completely separate physical server.
+ Multiple virtual machines on the same physical host are still
+ vulnerable to the complete failure of that host.</p>
+
</div>
</div>
<a name="Other+Optimizations"></a>