/docs/user/replication.html - Annotate - Metacat - Ecoinformatics Redmine

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+<!--
   * replication.html
+  *
   *      Authors: Chad Berkley
   *    Copyright: 2000 Regents of the University of California and the
   *               National Center for Ecological Analysis and Synthesis
   *  For Details: http://www.nceas.ucsb.edu/
   *      Created: 2001 January 23
   *      Version:
   *    File Info: '$ '
+  *
+  *
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 <HTML>
 <HEAD>
 <TITLE>Metacat</TITLE>
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+<link rel="stylesheet" type="text/css" href="./default.css">
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+</HEAD>
 <BODY>
   <table width="100%">
     <tr>
       <td class="tablehead" colspan="2"><p class="label">Replication</p></td>
       <td class="tablehead" colspan="2" align="right">
         <a href="./packages.html">Back</a> | <a href="./metacattour.html">Home</a> |
         <a href="./datafiles.html">Next</a>
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   <div class="header1">Table of Contents</div>
   <div class="toc1"><a href="#Intro">Metacat Replication</a></div>
     <div class="toc2"><a href="#DatabasedInfo">Databased Information</a></div>
     <div class="toc2"><a href="#Example">Example</a></div>
       <div class="toc3"><a href="#gamma">What happens with gamma?</a></div>
       <div class="toc3"><a href="#alpha">What happens with alpha?</a></div>
       <div class="toc3"><a href="#lamda">What happens with lamda?</a></div>
   <div class="toc1"><a href="#Certificates">Certificates</a></div>
     <div class="toc2"><a href="#GenerateCertificates">Generate Certificates on both the replication client and server.</a></div>
       <div class="toc3"><a href="#GenerateCertTomcat">Generate Certificate for Tomcat standalone (no Apache)</a></div>
       <div class="toc3"><a href="#GenerateCertApache">Generate Certificate for Apache/Tomcat</a></div>
     <div class="toc2"><a href="#RegisterPartner">Register the partner machines certificate</a></div>
   <a name="Intro"></a><div class="header1">Metacat Replication</div>
   <p>Metacat has built-in replication to allow different Metacat servers to
   share data between themselves. Metacat not only replicates XML documents but
   also data files. </p>
   <p>Metacat's hub feature allows it to replicate not only it's own server's original
   documents, but also those that were replicated from other servers.  This functionality
   allows for a more complex chaining replication structure.</p>
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+  <p>The replication scheme that Metacat uses is both push and pull.  There are
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+  several triggers that can start a replication mechanism: </p>
   <ul class="list1">
     <li><b>Delta-T monitoring</b> - at a set time interval a server checks each of the
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+    other servers in its list for updated documents</li>
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+    <li><b>INSERT trigger</b> - Whenever a document is inserted, the server notifies
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+    the remote hosts in its list that it has a new file available.</li>
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+    <li><b>UPDATE trigger</b> - Whenever a document is updated, the server notifies
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+    each server in its list of the update.</li>
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+    <li><b>File locking</b> - When a local user tries to alter a document on a local
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+    server that belongs to a remote server, the local server must first
     obtain a lock on that file.  Once the lock is obtained, the file can
     be updated, then it is force replicated out to each server in the list.
     The lock ensures that the remote copy is up to date and that an older
     file does not overwrite a newer one.  Only a documents home server
     can give a lock for that file to be altered.</li>
   </ul>
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   <a name="DatabasedInfo"></a><div class="header2">Databased Information</div>
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+  <p>Each server contains a list of servers to which it can replicate.  One-way
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+  replication is enabled by the 'replicate' and 'datareplicate' flags in the
   list.  The server list may look like the following.</p>
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+  <table border="1">
     <tr>
       <td><b>serverid</b></td>
       <td><b>server</b></td>
       <td><b>last_checked</b></td>
       <td><b>replicate</b></td>
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+      <td><b>datareplicate</b></td>
       <td><b>hub</b></td>
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+    </tr>
     <tr>
       <td>1</td>
       <td>localhost</td>
       <td>null</td>
       <td>0</td>
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+      <td>0</td>
       <td>0</td>
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+    </tr>
     <tr>
       <td>2</td>
       <td>alpha.nceas.ucsb.edu:8080/berkley/servlet/replication</td>
       <td>2001-01-22 14:52:12.1</td>
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+      <td>0</td>
       <td>0</td>
       <td>0</td>
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+    </tr>
     <tr>
       <td>3</td>
       <td>dev.nceas.ucsb.edu/Metacat/servlet/replication</td>
       <td>2001-01-23 9:10:02.5</td>
       <td>1</td>
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+      <td>1</td>
       <td>0</td>
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+    </tr>
   </table>
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+  <br>
   The server list is kept in a table in the database called xml_replication.
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+  Localhost must always be the first entry in the table and have a serverid of 1.
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+  The database fields are:
   <ul class="list1">
   <li><b>serverid</b> - a unique ID that is generated by the database when a new field is added.</li>
   <li><b>server</b> - this field always points to the partner server's replication servlet,
   hence the "servlet/replication" on the end of both of the sample servers.  Note
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+  that any port numbers (if your servlet engine is not running on port 80) must
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+  also be included. </li>
   <li><b>last_checked</b> - a system generated values that holds the last time that a check was
   made to see if replication needed to be performed.<li>
   <li><b>replicate</b> - flag that is set to 1 if you want this server to replicate XML
   metadata documents TO the remote host.  Note that if this flag is set to 0, datareplicate
   and hub fields have no meaning.</li>
   <li><b>datareplicate</b> - flag that is set to 1 if you want this server to copy data
   files to the remote host.  Note that this field has no meaning if replicate is not set to 1.</li>
   If this server is a hub to the remote host, the hub flag should be set to.
   <li><b>hub</b> - if this flag is set to true, this server will not only replicate it's own
   original documents, it will also replicate documents that were replicated to it.  Thus it
   acts as a replication hub to one or more other Metacat servers.</li>
   </ul>
   <a name="Example"></a><div class="header2">Example</div>
   Here we show an example setup of three replication servers.  We will discuss each.<br><br>
   First, note that in order for replication to occur, both partner servers must have
   each other in their respective tables or replication will not take place.  Also,
   certificates must be set up correctly on both servers in order for replication to
   work.  See the <a href="#Certificates">certificates</a> section below.<br><br>
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+  <table border="1">
     <tr>
       <td>host</td>
       <td>replication table</td>
     </tr>
     <tr>
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+     <td>gamma.nceas.ucsb.edu</td>
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+     <td>
       <table border="2">
         <tr>
           <td><b>server</b></td>
           <td><b>last_checked</b></td>
           <td><b>replicate</b></td>
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+          <td><b>datareplicate</b></td>
           <td><b>hub</b></td>
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+        </tr>
         <tr>
           <td>localhost</td>
           <td>null</td>
           <td>0</td>
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+          <td>0</td>
           <td>0</td>
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+        </tr>
         <tr>
           <td>alpha.nceas.ucsb.edu:8080/berkley/servlet/replication&nbsp;&nbsp;&nbsp;</td>
           <td>2001-01-22 14:52:12.1</td>
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+          <td>0</td>
           <td>0</td>
           <td>0</td>
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+        </tr>
         <tr>
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+          <td>lamda.nceas.ucsb.edu/Metacat/servlet/replication</td>
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+          <td>2001-01-23 9:10:02.5</td>
           <td>1</td>
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+          <td>1</td>
           <td>0</td>
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+        </tr>
       </table>
      </td>
     </tr>
     <tr>
       <td>alpha.nceas.ucsb.edu</td>
       <td>
         <table border="2">
           <tr>
             <td><b>server</b></td>
             <td><b>last_checked</b></td>
             <td><b>replicate</b></td>
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+            <td><b>datareplicate</b></td>
             <td><b>hub</b></td>
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+          </tr>
           <tr>
             <td>localhost</td>
             <td>null</td>
             <td>0</td>
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+            <td>0</td>
             <td>0</td>
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+          </tr>
           <tr>
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+            <td>gamma.nceas.ucsb.edu:8080/berkley/servlet/replication</td>
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+            <td>2001-01-21 11:33:12.7</td>
             <td>0</td>
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+            <td>1</td>
             <td>0</td>
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+          </tr>
           <tr>
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+            <td>lamda.nceas.ucsb.edu/Metacat/servlet/replication</td>
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+            <td>2001-01-23 10:22:02.5</td>
             <td>1</td>
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+            <td>0</td>
             <td>0</td>
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+          </tr>
         </table>
       </td>
     </tr>
     <tr>
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+      <td>lamda.nceas.ucsb.edu</td>
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+      <td>
         <table border="2">
           <tr>
             <td><b>server</b></td>
             <td><b>last_checked</b></td>
             <td><b>replicate</b></td>
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+            <td><b>datareplicate</b></td>
             <td><b>hub</b></td>
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+          </tr>
           <tr>
             <td>localhost</td>
             <td>null</td>
             <td>0</td>
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+            <td>0</td>
             <td>0</td>
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+          </tr>
           <tr>
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+            <td>gamma.nceas.ucsb.edu:8080/berkley/servlet/replication</td>
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+            <td>2001-01-21 11:33:12.7</td>
             <td>0</td>
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+            <td>0</td>
             <td>0</td>
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+          </tr>
           <tr>
             <td>alpha.nceas.ucsb.edu:8080/Metacat/servlet/replication</td>
             <td>2001-01-22 12:15:32.5</td>
             <td>1</td>
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+            <td>1</td>
             <td>1</td>
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+          </tr>
         </table>
       </td>
     </tr>
   </table>
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   <a name="gamma"></a><div class="header3">What happens with gamma?</div>
   <ul class="list1">
   <li>The localhost entry is required internally for replication to work on
       gamma.  As long as we see it there, we can safely disregard it.</li>
   <li>We see the entry for the alpha machine has all zeros in replicate,
       datareplicate and hub columns.  This means that gamma is configured to
       accept replication information from alpha.  (As we will see in a moment,
       alpha is not actually correctly configured to send data to gamma.)</li>
   <li>We see that the entry for the lamda machine has ones in the replicate
       and data replicate columns and a zero in the hub column.  This tells us
       that gamma will replicate it's original documents to lamda, assuming that
       lambda is configured to accept replication from gamma (we will see that it
       is).  However, because the hub value is zero, any documents that replicate
       to gamma will not be further replicated to lamda.</li>
   </ul>
   <a name="alpha"></a><div class="header3">What happens with alpha?</div>
   <ul class="list1">
   <li>The localhost entry is required internally for replication to work on
       alpha.  As long as we see it there, we can safely disregard it.</li>
   <li>We see that the entry for gamma has a zero in the replicate column.
       This means that all other entries are meaningless and can be disregarded.
       Even though there is a one in the datareplicate column on alpha and gamma
       is configured to accept replication from alpha, no replicationwill happen
       from alpha to gamma.</li>
   <li>We see that the entry for lamda is a one in the replicate column and zeros
       in the datareplicate and hub columns.  Assuming lamda is configured to
       accept replication from alpha, alpha will replicate metadata only to lamda
       (and indeed, we will see that lambda is set up to accept replication from
       alpha). </li>
   </ul>
   <a name="lamda"></a><div class="header3">What happens with lamda?</div>
   <ul class="list1">
   <li>The localhost entry is required internally for replication to work on
       lamda.  As long as we see it there, we can safely disregard it.</li>
   <li>We see that the entry for gamma has all zeros in replicate, datareplicate
       and hub, so lamba is set up to accept replication from gamma.  As we have
       already seen, gamma is correctly configured to replicate metadata and data
       to lambda.  We should see data and metadata replication from gamma to lamda.
   <li>We see that the entry for alpha has ones in the replicate datareplicate and
       hub columns.  There's a lot going on here:
     <ul class="list2">
     <li>First, lamda will replicate original metadata and data to alpha if
         alpha is configured to accept replication from lamda.  Because alpha
         has an entry for lambda, lamba will be allowed to replicate to alpha. </li>
     <li>Second, because the alpha entry has a one in the hub column, lambda
         will not only replicate it's original data, it will also replicate
         data that was replicated to it.  Remember that gamma was configured
         to replicate to lamda.  So any data or metadata that gamma sends to
         lambda will get further replicated to alpha.</li>
     <li>Finally, the alpha entry in the table allows the alpha server to
         replicate to lambda.  Since the alpha server is set up to replicate
         metadata only, we would expect any original metadata on alpha to
         wind up on lambda.</li>
     </ul>
   </ul>
   There is an html control panel for controling replication.  After
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+  <a href="./Metacatinstall.html">installing</a> Metacat, you can access
   it by going through the Metacat servlet context you have setup and calling up
   replControl.html.  For instance, if you setup a Metacat servlet instance
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+  called 'knb' you would probably type
   <div class="code">http://server.domain.com:8080/Metacat/style/skins/dev/replControl.html</div>
   The control panel is an easy interface for adding/removing/altering servers and
   starting the delta-T handler.  It will also allow you to 'force replicate' your
   server list.  This is useful if you want to initialize the state of one Metacat
   server from an existing state of another (i.e. copy all of the data from an existing
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+  server).</p>
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+  <a name="Certificates"></a><div class="header1">Certificates:</div>
   You will need to generate security certificates on both the replication client
   and server.  The certificates will be exchanged so that each machine understands
   that the other has access for replication.<br><br>
   The following are the steps to generate and exchange certificates on systems
   running Tomcat 5 and java 1.5.  Note that if Tomcat is running in conjunction with
   Apache, the process is somewhat different than if it is running standalone.
   <a name="GenerateCertificates"></a><div class="header2">Generate Certificates on both the replication client and server.</div>
   <a name="GenerateCertTomcat"></a><div class="header3">Generate Certificate for Tomcat standalone (no Apache)</div>
   <ul class="list1">
   <li>Generate keys in java default key store - this will create a secure key and put it
     into the binary certificates file located at $JAVA_HOME/lib/security/cacerts</li>
     <ul class="list2">
     <li>Run the command:
    	  <div class="code">keytool -genkey -alias &lt;aliasname&gt; -keyalg RSA -validity 800 -keystore cacerts</div>
      where &lt;aliasname&gt; is a unique name that you choose for this cert.  Something like "&lt;hostname-tomcat&gt"
      might be appropriate.</li>
     </ul>
   </li>
   <li>Sample values when creating certificate</li>
     <ul class="list2">
     <li>What is your first and last name? <b>myserver.nceas.ucsb.edu </b>
         (note: use the host name without port number)<li>
     <li>What is the name of your organizional unit? <b>NCEAS</b></li>
     <li>What is the name of your organizional unit? <b>UCSB</b></li>
     <li>What is the name of your City or Locality? <b>Santa Barbara</b></li>
     <li>What is the name of your State or Province? <b>California</b>
         (note: this is spelled in full)<li>
     <li>What is the two-letter country code for this unit? <b>US</b></li>
     </ul>
   <li>Generate certificate - this will pull the certificate you created from the cacerts file
       and put it into a local file</li>
     <ul class="list2">
     <li>Run the command:
       <div class="code">keytool -export -alias &lt;aliasname&gt; -file &lt;outputfile&gt;.cert -keystore cacerts</div>
       where &lt;aliasname&gt; is the same name you used when you created the certificate.  </li>
     <li>A file named &lt;outputfile&gt;.cert will be created in the same directory where you run the keytool
       command.  You can name the output file anything you like, but keep in mind that it will get sent to the
       partner machine used for replication.  The filename should have have enough meaning that someone who sees
       it on that machine can have some idea where it came from.  Again, something like "&lt;hostname&gt;-tomcat.cert"
       will suffice.</li>
     </ul>
   </li>
   <li>Enable SSL in Tomcat
     <ul class="list2">
     <li>Edit the Tomcat server file at $TOMCAT_HOME/conf/server.xml</li>
     <li>uncomment the section that starts with "&lt;Connector port="8443" ...</li>
   	<li>add another attribute to that section that reads:
   	  <div class="code">keystoreFile="&lt;JAVA_HOME&gt;/lib/security/cacerts"</div>
   	  where $JAVA_HOME should be the actual java path.
   	</li>
   	</ul>
   </li>
   </ul>
   <a name="GenerateCertApache"></a><div class="header3">Generate Certificate for Apache/Tomcat</div>
   <ul class="list1">
   <li>Generate keys using openssl
     <ul class="list2">
     <li>Run the command:
    	  <div class="code">   openssl req -new -out REQ.pem -keyout &lt;hostname&gt;-apache.key</div>
     </li>
     </ul>
   </li>
   <li>Sample values when creating certificate</li>
     <ul class="list2">
     <li>Country Name (2 letter code) [AU]: <b>US</b></li>
     <li>State or Province Name (full name) [Some-State]: <b>California</b>
         (note: this is spelled in full)</li>
     <li>Locality Name (eg, city) []: <b>Santa Barbara</b></li>
     <li>Organization Name (eg, company) [Internet Widgits Pty Ltd]: </b>UCSB</b></li>
     <li>Organizational Unit Name (eg, section) []: <b>NCEAS</b></li>
     <li>Common Name (eg, YOUR name) []: <b>myserver.mydomain.edu</b>
         (note: use the host name without port number)</li>
     <li>Email Address []:  <b>administrator@mydomain.edu</b></li>
     <li>A challenge password []: (note: leave blank)</li>
     <li>An optional company name []: (note: leave blank)</li>
     </ul>
   </li>
   <li>Generate certificate - this will create a local file with your certificate</li>
     <ul class="list2">
     <li>Run the command:
       <div class="code">openssl req -x509 -days 800 -in REQ.pem -key &lt;hostname&gt;-apache.key -out &lt;hostname&gt;-apache.crt</div>
       where &lt;aliasname&gt; is the same name you used when you created the certificate.  </li>
     <li>A file named &lt;outputfile&gt;.cert will be created in the same directory where you run the keytool
       command.  You can name the output file anything you like, but keep in mind that it will get sent to the
       partner machine used for replication.  The filename should have have enough meaning that someone who sees
       it on that machine can have some idea where it came from.  Again, something like "&lt;hostname&gt;-tomcat.cert"
       will suffice.</li>
     </ul>
   </li>
   <li>Enter the certificate into apache security configuration - you need to register the certificate
       in the local Apache instance.  Note that the security files may be in a different place depending
       on how you installed apache.</li>
     <ul class="list2">
     <li>Copy the certificate and key file to the apache ssl directories and enable ssl.</li>
     <li>For Ubuntu/Debian based systems:
       <ul class="list3">
       <li>sudo cp &lt;hostname&gt;-apache.crt /etc/ssl/certs</li>
       <li>sudo cp &lt;hostname&gt;-apache.key /etc/ssl/private</li>
       <li>As root edit /etc/apache2/sites-available/default.  In the VirtualHost section
           after the DocumentRoot line, add:<br>
           SSLEngine on<br>
           SSLOptions +FakeBasicAuth +ExportCertData +CompatEnvVars +StrictRequire<br>
           SSLCertificateFile /etc/ssl/certs/server.crt<br>
           SSLCertificateKeyFile /etc/ssl/private/server.key<br>
       </li>
       </ul>
     </li>
     </ul>
     <ul class="list2">
     <li>For other systems:
       <ul class="list3">
       <li>sudo cp &lt;hostname&gt;-apache.crt $APACHE_HOME/conf/ssl.crt</li>
       <li>sudo cp &lt;hostname&gt;-apache.key $APACHE_HOME/conf/ssl.key</li>
       <li> ADD STEPS TO ENABLE SSL ON NON_DEBIAN SYSTEMS HERE</li>
       </ul>
     </li>
     </ul>
   <li>scp &lt;hostname&gt;-apache.crt to the replication partner machine.</li>
   </ul>
   <a name="RegisterPartner"></a><div class="header2">Register the partner machines certificate.</div>
   At this point, you have created a certificate for each replication server and
   scp-ed them across to each other.  Now you need to import the remote server's
   certificate on the local machine.  Perform the following steps for each
   replication server.
   <ul class="list1">
   <li>Import the remote certificate by running:
     <div class="code">keytool -import -alias &lt;remotehostalias&gt; -file &lt;remotehostfilename&gt;.cert -keystore cacerts</div>
     where the &lt;remotehostfilename&gt; is the certificate file you created on the remote machine and
     copied to this machine.  The &lt;remotehostalias&gt; is the name the certificate will use in
     the keystore.  It should be something that identifies the remote host.
   </li>
   <li>Restart Apache and Tomcat on both replication machines</li>
   </ul>
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+  <a href="./packages.html">Back</a> | <a href="./metacattour.html">Home</a> |
   <a href="./datafiles.html">Next</a>
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+  </ul>
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