MarkLogic 9 Product Documentation

Flexible Replication Guide — Chapter 3

Replication Security

The flexrep-admin role is required to configure replication. The user who will access the Replica App Server when pushing, or access the Master App Server when pulling, requires the flexrep-user role. Though you will typically configure replication as the Admin user, you should create a unique replication user to be associated with the replication tasks. The replication user must be given the flexrep-user role and have the privileges necessary to update the domain content on both the Master and Replica App Servers.

If you configure your replication target to use any of the security schemes described in this section, the Target URL must start with https.

It is a best practice to create a secure credential, as described in Secure Credentials in the Security Guide, to communicate with the replication target. To do so, select the name of the secure credential from the credential id menu.

As an alternative to secure credentials and mostly to provide backward compatibility with previous versions of MarkLogic, you can configure SSL on your Master and Replica App Servers to encrypt the replicated data passed between them. For details on configuring SSL on App Server, see the Configuring SSL on App Servers in the Security Guide.

If SSL on the Replica App Server is configured to require a client certificate from the Master, paste the PEM-encoded client certificate and client key in the fields located at the bottom of the Database Replication Target Administration page. If the client key is encrypted, you must also specify a pass phase.

The same security configuration applies when configuring the Replica App Server for pull replication, if the Master App Server requires a client certificate from the Replica. For details on how to configure pull replication, see Creating a Pull Replication Task

Defining Replicated Domains

Before you can define replicated domains, you must enable CPF as described in Configuring a Flexible Replication Pipeline for the Master Database.

CPF domains are described in detail in the Understanding and Using Domains chapter in the Content Processing Framework Guide Guide. The purpose of this section is to describe how to create a domain that defines the scope of the documents in the Master database to be replicated to the Replica database.

Each domain must contain a unique set of documents. No single document can be in more than one domain.

The following procedure describes how to create a new domain for defining the scope of the replicated documents. By default, CPF creates a Default Master domain to replicate from the / root directory of the Master database. The / root means that the document URIs must be preceded by a /, such as /foo.xml or /content/foo.xml. You can also set the Document Scope of the domain to replicate a user collection or an individual document.

1. To replicate a portion of a database, you can create another domain. For example, you can create a domain that specifies the documents in the /projects/Baz/ directory on the Master database, as shown below.

   

   You may receive a warning that this domain overlaps with the Default Master domain. This means that the both the Baz domain and the Default Master domain are configured to replicate the documents in the /projects/Baz/ directory. You cannot have any document that is in more than one domain, so you must either delete or modify the Default Master to resolve this conflict.

   If you want to create a domain to replicate the entire database, you can assign a default collection to all of your users and then set the Document Scope to Collections and the URI to the name of the default collection. For details on how to establish a default collection for a user, see Creating a User in the Administrator's Guide.

2. Select Pipelines in the navigation frame and select the Flexible Replication and Status Change Handling pipelines. These are the minimum pipelines required for replication. You can select other pipelines, as required for your configuration.

   

Configuring Replication App Servers

As described in Creating a Replication App Server, in a push replication configuration, the Replica database must be connected to a Replication App Server. In a pull replication configuration, the Master database must be connected to a Replication App Server. This section goes into more detail on creating and configuring Replication App Servers.

1. Create a Replication App Server by clicking Create in the Application Server section of the Flexible Replication Administration page:

   

   The Server Name, Root, and Database fields are preconfigured and should not be changed.

2. Enter a unique port number for the App Server:

   

   The purpose of the other fields in the HTTP Server Configuration page are described in Creating a New HTTP Server in the Administrator's Guide. If you are going to configure SSL on the App Server to require a client certificate, you must specify the certificate in the Database Replication Target Administration configuration page, as described in Replication Security.

   For example, if you are configuring the Master database to push updates to a Replica App Server that requires a client certificate, you must include a client certificate in the Database Replication Target Administration configuration page for the Master database. If you are configuring a Replica App Server to pull updates from the Master database that requires a client certificate, you must you must include a client certificate in the Replication Pull configuration page for the Replica database. For details on providing a client certificate for either a push or pull replication configuration, see Replication Security.

Configuring Push Replication

This section describes how to configure your Master database for Push Replication.

Before you can configure a replication target, you must have content processing enabled for the Master database. After configuring push replication, you must create a scheduled task, as described in Creating a Push-Local-Forests Replication Task.

1. Under Databases, click the Master database.
2. Click Flexible Replication under the Master database.
3. Locate the Content Processing section on the Flexible Replication Administration page and click on the domain name.

   

4. Click Create to configure replication for the domain:

   

5. Click Create to configure a replication target for the domain:

   

6. In the Database Replication Target Administration page, specify a target name and one or more target URLs that include the hostname and port number you specified for your Replica App Servers in Creating a Replication App Server. The Retry Seconds Min/Max and Documents Per Batch setting are for scheduled tasks, as described in Creating a Scheduled Replication Task.

   Under Authentication, specify the username and password for a user assigned the flexrep-user role. This user must have the same username/password as the user on the Master App Server who creates and updates the documents. This user needs to have sufficient permissions on the target system to insert and update the replicated documents.

   Because Flexible Replication passes through the permissions set on the Master App Server when replicating, the user on the target must have permissions to update the document later on. Permissions can either be configured by the administrator on both the Master and Replica App Server, or you can use a filter to adjust the document permissions so the target user can later update the document, as described in Adding Document Permissions.

   You can optionally disable pushing replication to the target by setting Enabled to false. Do not set the Replicate CPF option to true without the direction from MarkLogic Customer Support.

   

7. If the Replica App Server requires a client certificate, the Target URL must start with HTTPS. Paste the client certificate, client key and pass phrase (if the client key is encrypted) in the fields located at the bottom of the Database Replication Target Administration page. For details on how to configure the Master to provide a client certificate, see Replication Security.

Creating a Scheduled Replication Task

Regardless of whether you configure replication as push or pull, you must create a scheduled task to periodically replicate updated content on the Master to the Replicas. A scheduled replication task does the following:

• Moves existing content that was on the Master before replication was configured (zero-day replication).
• Provides a retry mechanism in the event the initial replication fails.
• Replicates deletes on the Master to the Replica.
• Provides the ability to pull data from a Master server located outside a firewall.

There are three types of scheduled tasks, as described in the table below.

For all scheduled replication tasks, the replication retry configuration is a combination of the scheduled task frequency settings and the target settings, Retry Seconds Min, Retry Seconds Max, and Document Per Batch.

The task type in the Scheduled Task Configuration page indicates the interval at which each scheduled replication task is to run. In most configurations, the task type will be minutely. For details on configuring scheduled tasks, see Scheduling Tasks in the Administrator's Guide.

The Retry Seconds Min/Max settings in the Database Replication Target Administration page indicate the minimum and maximum number of seconds any documents that failed to replicate are eligible for replication retries. In a push configuration, the Documents Per Batch setting specifies how many documents that have failed to replicate are to be retried during each scheduled task interval. In a pull configuration, the Documents Per Batch setting specifies the total number of replicated documents (retries of failed documents and newly added or updated documents) that are to be pulled from the Master during each scheduled task interval.

For example, the retry minimum is 30 seconds, the retry maximum is 300 seconds (five minutes) and the scheduled replication task period is every one minute. If a document fails replication, it is eligible to be retried in 30 seconds. This means that MarkLogic Server will attempt to replicate the document at the next minute interval. The retry interval is doubled each time the document fails to replicate until the interval reaches the maximum retry setting, at which time the retry interval remains at the maximum. So, if the document in our example fails a second time, it will be eligible for retry in one minute. Should the document fail to replicate the second time, the retry interval is set to two minutes, and so on until the interval reaches the five-minute retry maximum setting, after which MarkLogic Server tries to replicate the document every five minutes.

The Documents Per Batch setting also plays a role with replication retries. For example, if the batch value is one and five documents have failed to replicate, then MarkLogic Server will only attempt to retry one failed document that is eligible for replication retries during each scheduled task interval. The document selected for replication retry is the earliest eligible document.

Though the Documents Per Batch setting is 1 by default, a more typical value is in the range of 10 - 100. If there is a large number of documents to be replicated in a zero-day fashion, you can maximize the load speed by closely matching the scheduled interval with the Documents Per Batch setting, so that the maximum number of documents are loaded within the time interval. For example, if your scheduled interval is one minute and you have determined that you can replicate a maximum of 250 documents per minute, then the optimum Documents Per Batch setting would be 250.

When a flexible replication domain includes multiple targets, the scheduled task will use the smallest of the configured Documents per Batch settings. So if one target has Documents per Batch set to 1, and another has Documents per Batch set to 100, the scheduled task will use a batch size of 1.

Configuring Pull Replication

Pull Replication is useful when a Replica is behind a firewall that only allows its internal servers to pull from a Master server outside the firewall. This section describes how to configure your Replica database for Pull Replication.

If the Replica is to act as a Master for another Replica, then you must have CPF enabled on the Replica, as described in Configuring a Flexible Replication Pipeline for the Master Database. However, if the Replica has CPF installed and it is not to act as a Master, then you must disable the Flexible Replication pipeline on the Replica.

The procedure for configuring Pull Replication on the Master and Replica databases is as follows:

1. On a Master host, define a replication target for the Master Content Processing Domain with push replication disabled. You can do this by either not defining a target URL in the target configuration page and enabling the replication target.

   

2. Under Databases, click the Replica database.
3. Click Flexible Replication under the Replica database.
4. Create a Pull Replication Task, as described in Creating a Pull Replication Task.
5. Under Pull Configuration, click Create:

   

6. On a Master host, obtain the Master domain id from the Database Domain Replication Summary page:

   

7. On a Master host, obtain the Replica target id from the Database Domain Replication Administration page. If a Replica target does not exist, create one, as described in Configuring Push Replication, Step 5.

   

8. In the Replication Pull Administration page on the Replica host, enter a pull name, the domain id of the Master, the target id of the Replica, and one or more pull URLs for the Master App Servers. Fill in the username and password fields required to access the Master App Servers.

   

9. You can optionally specify a client certificate, if one is required by the Master App Server. For details on how to configure the Replica to provide a client certificate, see Replication Security.

Configuring Alerting With Flexible Replication

Combining alerting with flexible replication is often referred to as QBFR (Query-Based Flexible Replication). Query-based flexible replication enables customizable information sharing (using filters) between systems, allowing for the easy and secure distribution of portions of data even across disconnected, intermittent, and latent networks.

This type of replication is based on a query (an alert) that triggers because of an event that matches that query. A user can have more than one alert, in which case they would receive documents that match any of their alerts. In addition to queries, the permissions for a user are taken into account. The user will only receive replicated content that they have permission to view in the database. If the permissions change, the replica will be updated accordingly. Most often query-based flexible replication is a pull configuration, but it can also be set up as a push configuration.

By setting up alerts, replication takes place any time content in the database matches that query. Any new or updated content within the domain scope will cause all matching rules or alerts to perform their corresponding action. Query-based flexible replication can be used with filters to share specific documents or parts of documents. Filters can be set up in either a push or pull configuration.

To set up query-based flexible replication, you need to have the environment for flexible replication already configured. See Flexible Replication Quick Start for information on setting up flexible replication using the Admin UI. Configuring Query-based Replication using the REST API in the Scripting Administrative Tasks Guide explains how to set up query-based flexible replication including alerts using scripting and REST.

QBFR users should have the flexrep-user role. QBFR targets will only replicate documents for which the associated user has read permission, as in normal MarkLogic security. Your configuration will most likely have additional or more complex permissions on documents.

This section contains these topics:

• Configuring Alerts
• Using QBFR

xquery version "1.0-ml";
import module namespace alert = "http://marklogic.com/xdmp/alert"
  at "/MarkLogic/alert.xqy";
alert:config-insert(
  alert:make-config(
    "http://acme.com/alerting",
    "qbfr", "alerting rules for query-based flexrep",
<alert:options/>))

xquery version "1.0-ml";
import module namespace alert = "http://marklogic.com/xdmp/alert"
  at "/MarkLogic/alert.xqy";
alert:action-insert("http://acme.com/alerting",
  alert:make-action(
    "log", "QBFR log action",
    xdmp:database("master-modules"), "/", "/log.xqy",
<alert:options/>))'

xquery version "1.0-ml";
import module namespace alert = "http://marklogic.com/xdmp/alert"
  at "/MarkLogic/alert.xqy";
let $domain := "my-cpf-domain"
let $cfg := flexrep:configuration-get($domain, fn:true())
let $domain-id := 
flexrep:configuration-insert(
  flexrep:configuration-set-alerting-uri($cfg,
    flexrep:domain-alerting-uri($domain-id)))

xquery version "1.0-ml"; 
import module namespace flexrep =   "http://marklogic.com/xdmp/flexible-replication" 
  at "/MarkLogic/flexrep.xqy";
let $domain := "my-cpf-domain"
let $cfg := flexrep:configuration-get($domain, fn:true())
let $target-id := flexrep:configuration-target-get-id($cfg, "QBFR target")
let $user-id := xdmp:user("User1")
flexrep:configuration-insert(
  flexrep:configuration-target-set-user-id(
$cfg, $target-id, $user-id))

xquery version "1.0-ml";
import module namespace alert = "http://marklogic.com/xdmp/alert" 
  at "/MarkLogic/alert.xqy";
alert:make-rule(
  "nucleic acids email", 
  "Alert me to anything concerning nucleic acids",
  0, 
  cts:or-query((
    cts:word-query("dna"),
    cts:word-query("rna")
   )),
  "email",
  <alert:options>
    <alert:email-address>me@somedomain.com</alert:email-address>
  </alert:options>
)

Backing Up, Restoring, and Clearing the Master and Replica Databases

The configuration for flexible replication is stored in the Master and Replica databases. Clearing a Master database has the effect of deleting the target configurations, as well as all document-level information about target replication status. When you backup a Master database, you are also saving the replication configuration information. Should you restore that database to another cluster, the flexible replication configuration will also be present for the database in that cluster. Should you restore a database that is not configured for replication to one that was previously configured for replication, the replication configuration will be lost.

Before clearing or restoring a Master database, you can save the replication configuration by calling the flexrep:configuration-get function. Once the Master is cleared or restored, the replication configuration can be restored using the flexrep:configuration-insert function. Alternatively you can recreate the replication configuration programmatically, as described in Scripting Flexible Replication Configuration in the Scripting Administrative Tasks Guide.

Clearing a Replica database impacts the Master in that it no longer understands the status of the target. The same issues related to backing up and restoring the Master database described above also apply to backing up and restoring the Replica database. If the target status is lost on the Replica, new updates will replicate to the target, but the Master will not know that the older, unchanged documents are missing. Before clearing or restoring a Replica database, disable replication. After clearing or restoring the Replica database, delete the existing target on the Master, create a new target with the same configuration as the old one, and re-enable replication. The scheduled task will gradually populate the new target's database with all the documents in the domain.

If you have pull replication configured on the Replica, then you can save the configuration by calling the flexrep:pull-get function before clearing the database. After clearing or restoring the Replica database, you can restore the pull replication configuration by calling the flexrep:pull-insert function.

xquery version "1.0-ml"; 
import module namespace flexrep = "http://marklogic.com/xdmp/flexible-replication" 
  at "/MarkLogic/flexrep.xqy";
  flexrep:binary-chunk-uris(xs:dateTime("2014-10-01T08:00:00"))
  (: Returns the URIs of binary chunks that were created before
2014-10-01T08:00:00. :)

xquery version "1.0-ml"; 
import module namespace flexrep = "http://marklogic.com/xdmp/flexible-replication" 
  at "/MarkLogic/flexrep.xqy";
let $delete :=
<flexrep:delete xmlns:flexrep="http://marklogic.com/xdmp/flexible-replication">
<doc:uri xmlns:doc="xdmp:document-load">/content/foo.xml</doc:uri>
<flexrep:last-updated>2010-09-28T14:35:12.714-08:00</flexrep:last-updated>
</flexrep:delete>
return flexrep:delete($delete) 
(: Applies the specified delete element to /content/foo.xml.  This
effectively deletes the document from both the Master and Replica
databases. :)