Replication

Replication agents are central to Adobe Experience Manager (AEM) as the mechanism used to:

• Publish (activate) content from an Author to a Publish environment.
• Explicitly flush content from the Dispatcher cache.
• Return user input (for example, form input) from the Publish environment to the Author environment (under control of the Author environment).

Requests are queued to the appropriate agent for processing.

Replicating from Author to Publish

Replication, to a Publish instance or Dispatcher, takes place in several steps:

• the Author requests that certain content be Published (activated); this can be initiated by a manual request, or by automatic triggers which have been preconfigured.

• the request is passed to the appropriate default replication agent; an environment can have several default agents that are always selected for such actions.

• the replication agent “packages” the content and places it in the replication queue.

• in the Websites tab the colored status indicator is set for the individual pages.

• the content is lifted from the queue and transported to the Publish environment using the configured protocol; usually this is HTTP.

• a servlet in the Publish environment receives the request and publishes the received content; the default servlet is https://localhost:4503/bin/receive.

• multiple Author and Publish environments can be configured.

Replicating from Publish to Author

Some features allow users to enter data on a Publish instance.

Sometimes, a type of replication known as reverse replication, is needed to return this data to the Author environment from where it is redistributed to other Publish environments. Due to security considerations, any traffic from the Publish to the Author environment must be strictly controlled.

Reverse replication uses an agent in the Publish environment which references the Author environment. This agent places the data into an outbox. This outbox is matched with replication listeners in the Author environment. The listeners poll the outboxes to collect any data entered and then distribute it as necessary. This ensures that the Author environment controls all traffic.

In other cases, such as for Communities features (for example, forums, blogs, comments, and reviews), the amount of user-generated content (UGC) being entered in the Publish environment is difficult to efficiently synchronize across AEM instances using replication.

AEM Communities never uses replication for UGC. Instead, the deployment for Communities requires a common store for UGC (see Community Content Storage).

Replication - Out of the Box

The we-retail website that is included in a standard installation of AEM can be used to illustrate replication.

To follow this example, and use the default replication agents, install AEM with:

• the Author environment on port 4502
• the Publish environment on port 4503

Replication (Author to Publish)

1. Navigate to the support page on the Author environment.
   https://localhost:4502/content/we-retail/us/en/experience.html <pi>
2. Edit the page so you can add some new text.
3. Activate Page so you can publish the changes.
4. Open the support page on the Publish environment:
   https://localhost:4503/content/we-retail/us/en/experience.html
5. You can now see the changes that you entered on Author.

This replication is actioned from the Author environment by the:

• Default Agent (publish)
  This agent replicates content to the default Publish instance.
  Details of this (configuration and logs) can be accessed from the Tools console of the Author environment; or:
  https://localhost:4502/etc/replication/agents.author/publish.html.

Replication Agents - Out of the Box

The following agents are available in a standard AEM installation:

• Default Agent
  Used for replicating from Author to Publish.

• Dispatcher Flush
  This is used for managing the Dispatcher cache. See Invalidating Dispatcher Cache from the Authoring Environment and Invalidating Dispatcher Cache from a Publishing Instance for more information.

• Reverse Replication
  Used for replicating from Publish to Author. Reverse replication is not used for Communities features, such as forums, blogs, and comments. It is effectively disabled as the outbox is not enabled. Use of reverse replication would require custom configuration.

• Static Agent
  This is an “Agent that stores a static representation of a node into the filesystem.”
  For example, with the default settings, content pages and dam assets are stored under /tmp, either as HTML or the appropriate asset format. See the Settings and Rules tabs for the configuration.
  This was requested so that when the page is requested directly from the application server the content can be seen. This is a specialized agent and (probably) is not required for most instances.

Replication Agents - Configuration Parameters

When configuring a replication agent from the Tools console, four tabs are available within the dialog:

Settings

• Name

  A unique name for the replication agent.

• Description

  A description of the purpose this replication agent serves.

• Enabled

  Indicates if the replication agent is enabled.

  When the agent is enabled, the queue is shown as:

  • Active when items are being processed.
  • Idle when the queue is empty.
  • Blocked when items are in the queue, but cannot be processed; for example, when the receiving queue is disabled.

• Serialization Type

  The type of serialization:

  • Default: Set if the agent is to be automatically selected.
  • Dispatcher Flush: Select this if the agent is to be used for flushing the Dispatcher cache.

• Retry Delay

  The delay (waiting time in milliseconds) between two retries, should a problem be encountered.

  Default: 60000

• Agent User Id

  Depending on the environment, the agent uses this user account to:

  • collect and package the content from the Author environment
  • create and write the content on the Publish environment

  Leave this field empty to use the system user account (the account defined in sling as the administrator user; by default this is admin).

  CAUTION

  For an agent on the Author environment this account must have read access to all paths that you want to have replicated.

  CAUTION

  For an agent on the Publish environment this account must have the create/write access required to replicate the content.

  NOTE

  This can be used as a mechanism for selecting specific content for replication.

• Log Level

  Specifies the level of detail to be used for log messages.

  • Error: only errors are logged
  • Info: errors, warnings, and other informational messages are logged
  • Debug: a high level of detail is used in the messages, primarily for debug purposes

  Default: Info

• Use for reverse replication

  Indicates whether this agent is used for reverse replication; returns user input from the Publish to Author environment.

• Alias update

  Selecting this option enables alias or vanity path invalidation requests to Dispatcher. Also, see Configuring a Dispatcher Flush Agent.

Transport

• URI

  This specifies the receiving servlet at the target location. In particular, you can specify the hostname (or alias) and context path to the target instance here.

  For example:

  • A Default Agent may replicate to https://localhost:4503/bin/receive
  • A Dispatcher Flush agent may replicate to https://localhost:8000/dispatcher/invalidate.cache

  The protocol specified here (HTTP or HTTPS) determines the transport method.

  For Dispatcher Flush agents, the URI property is used only if you use path-based virtualhost entries to differentiate between farms, you use this field to target the farm to invalidate. For example, farm #1 has a virtual host of www.mysite.com/path1/* and farm #2 has a virtual host of www.mysite.com/path2/*. You can use a URL of /path1/invalidate.cache to target the first farm and /path2/invalidate.cache to target the second farm.

• User

  The user name of the account to be used for accessing the target.

• Password

  Password for the account to be used for accessing the target.

• NTLM Domain

  Domain for NTML authentication.

• NTLM Host

  Host for NTML authentication.

• Enable relaxed SSL

  Enable if you want self-certified SSL certificates to be accepted.

• Allow expired certs

  Enable if you want expired SSL certificates to be accepted.

Proxy

The following settings are only needed if a proxy is needed:

• Proxy Host

  Hostname of the proxy used for transport.

• Proxy Port

  Port of the proxy.

• Proxy User

  The user name of the account to be used.

• Proxy Password

  Password of the account to be used.

• Proxy NTLM Domain

  The proxy NTLM domain.

• Proxy NTLM Host

  The proxy NTLM domain.

Extended

• Interface

  Here you can define the socket interface to bind to.

  This sets the local address to be used when creating connections. If this is not set, the default address is used. This is useful for specifying the interface to use on multi-homed or clustered systems.

• HTTP Method

  The HTTP method to be used.

  For a Dispatcher Flush agent, this is nearly always GET and should not be changed (POST would be another possible value).

• HTTP Headers

  These are used for Dispatcher Flush agents and specify elements that must be flushed.

  For a Dispatcher Flush agent the three standard entries should not need changing:

  • CQ-Action:{action}
  • CQ-Handle:{path}
  • CQ-Path:{path}

  These are used, as appropriate, to indicate the action to be used when flushing the handle or path. The subparameters are dynamic:

  • {action} indicates a replication action

  • {path} indicates a path

  They are substituted by the path/action relevant to the request and therefore do not need to be “hardcoded”:

  NOTE

  If you have installed AEM in a context other than the recommended default context, then you must register the context in the HTTP Headers. For example:
  CQ-Handle:/<*yourContext*>{path}

• Close Connection

  Enable so you can close the connection after each request.

• Connect Timeout

  Timeout (in milliseconds) to be applied when trying to establish a connection.

• Socket Timeout

  Timeout (in milliseconds) to be applied when waiting for traffic after a connection has been established.

• Protocol Version

  Version of the protocol. For example, 1.0 for HTTP/1.0.

Triggers

These settings are used to define triggers for automated replication:

• Ignore default

  If checked, the agent is excluded from default replication; this means it is not used if a content author issues a replication action.

• On Modification

  Here a replication by this agent is automatically triggered when a page is modified. Used for Dispatcher Flush agents, but also for reverse replication.

• On Distribute

  If checked, the agent automatically replicates any content that is marked for distribution when it is modified.

• On-/Offtime reached

  This triggers automatic replication (to activate or deactivate a page as appropriate) when the ontimes or offtimes defined for a page occur. This is primarily used for Dispatcher Flush agents.

• On Receive

  If checked, the agent chains replicate whenever receiving replication events.

• No Status Update

  When checked, the agent does not force a replication status update.

• No Versioning

  When checked, the agent does not force versioning of activated pages.

Configuring your Replication Agents

For information about connecting replication agents to the Publish instance using MSSL, see Replicating Using Mutual SSL.

Configuring your Replication Agents from the Author Environment

From the Tools tab in the Author environment, you can configure replication agents that reside in either the Author environment (Agents on Author) or the Publish environment (Agents on Publish). The following procedures illustrate the configuration of an agent for the Author environment, but can be used for both.

1. Access the Tools tab in AEM.

2. Click Replication (left pane to open the folder).

3. Double-click Agents on Author (either the left or the right pane).

4. Click the appropriate agent name (which is a link) to show detailed information on that agent.

5. Click Edit so the configuration dialog box is opened:

   

6. The values provided should be sufficient for a default installation. If you make changes, click OK to save them (see Replication Agents - Configuration Parameters for information on individual parameters).

Configuring Reverse Replication

Reverse replication is used to get user content generated on a Publish instance back to an Author instance. This is commonly used for features such as surveys and registration forms.

For security reasons, most network topologies do not allow connections from the “Demilitarized Zone” (a subnetwork that exposes the external services to an untrusted network such as the Internet).

As the Publish environment is usually in the DMZ, to get content back to the Author environment the connection must be initiated from the Author instance. This is done with:

• an outbox in the Publish environment where the content is placed.
• an agent (publish) in the Author environment which periodically polls the outbox for new content.

To do this, you need:

A reverse replication agent in the Author environment – Acts as the active component to collect information from the outbox in the Publish environment:

If you want to use reverse replication, ensure that this agent is activated.

A reverse replication agent in the Publish environment (an outbox) – The passive element as it acts as an “outbox”. User input is placed here, from where it is collected by the agent in the Author environment.

Configuring Replication for Multiple Publish Instances

After installation, a default agent is already configured for replication of content to a Publish instance running on port 4503 of the localhost.

To configure replication of content for an additional Publish instance, create and configure a new replication agent:

1. Open the Tools tab in AEM.

2. Select Replication, then Agents on Author in the left panel.

3. Select New….

4. Set the Title and Name, then select Replication Agent.

5. Click Create so you can create the agent.

6. Double-click the new agent item so the configuration panel opens.

7. Click Edit - the Agent Settings dialog box opens - the Serialization Type is already defined as Default, this must remain so.

   • In the Settings tab:

     • Activate Enabled.

     • Enter a Description.

     • Set the Retry Delay to 60000.

     • Leave the Serialization Type as Default.

   • In the Transport tab:

     • Enter the required URI for the new Publish instance; for example,
       https://localhost:4504/bin/receive.

     • Enter the site-specific user account used for replication.

     • You can configure other parameters as required.

8. Click OK.

You can then test the operation by updating, then publishing, a page in the Author environment.

The updates appear on all Publish instances that have been configured as above.

If you encounter any problems, you can check the logs on the Author instance. Depending on the level of detail required you can also set the Log Level to Debug using the Agent Settings dialog as above.

Configuring a Dispatcher Flush agent

Default agents are included with the installation. However, a certain configuration is still needed and the same applies if you are defining a new agent:

1. Open the Tools tab in AEM.

2. Click Deployment.

3. Select Replication and then Agents on Publish.

4. Double-click the Dispatcher Flush item to open the overview.

5. Click Edit - the Agent Settings dialog box opens:

   • In the Settings tab:

     • Activate Enabled.

     • Enter a Description.

     • Leave the Serialization Type as Dispatcher Flush, or set it as such if creating an agent.

     • (optional) Select Alias update to enable alias or vanity path invalidation requests to Dispatcher.

   • In the Transport tab:

     • Enter the required URI for the new Publish instance; for example,
       https://localhost:80/dispatcher/invalidate.cache.

     • Enter the site-specific user account used for replication.

     • You can configure other parameters as required.

   For Dispatcher Flush agents, the URI property is used only if you use path-based virtualhost entries to differentiate between farms, you use this field to target the farm to invalidate. For example, farm #1 has a virtual host of www.mysite.com/path1/* and farm #2 has a virtual host of www.mysite.com/path2/*. You can use a URL of /path1/invalidate.cache to target the first farm and /path2/invalidate.cache to target the second farm.

   NOTE

   If you have installed AEM in a context other than the recommended default context, configure the HTTP Headers in the Extended tab.

6. Click OK.

7. Return to the Tools tab, from here you can Activate the Dispatcher Flush agent (Agents on Publish).

The Dispatcher Flush replication agent is not active on the Author. You can access the same page in the Publish environment by using the equivalent URI; for example, https://localhost:4503/etc/replication/agents.publish/flush.html.

Controlling Access to Replication Agents

Access to the pages used to configure the replication agents can be controlled by using user and/or group page permissions on the etc/replication node.

Configuring your Replication Agents from CRXDE Lite

Various parameters of your replication agents can be configured using CRXDE Lite.

If you navigate to /etc/replication, you can see the following three nodes:

• agents.author
• agents.publish
• treeactivation

The two agents hold configuration information about the appropriate environment, and are only active when that environment is running. For example, agents.publish is only used in the Publish environment. The following screenshot shows the Publish agent in the Author environment, as included with AEM WCM:

Monitoring your Replication Agents

To monitor a replication agent:

1. Access the Tools tab in AEM.

2. Click Replication.

3. Double-click the link to agents for the appropriate environment (either the left or the right pane). For example, Agents on Author.

   The resulting window shows an overview of all your replication agents for the Author environment, including their target and status.

4. Click the appropriate agent name (which is a link) to show detailed information on that agent:

   

   Here you can do the following:

   • See whether the agent is enabled.

   • See the target of any replications.

   • See whether the replication queue is active (enabled).

   • See whether there are any items in the queue.

   • Refresh or Clear to update the display of queue entries. This helps you see that items enter and leave the queue.

   • View Log to access the log of any actions by the replication agent.

   • Test Connection to the target instance.

   • Force Retry on any queue items, if necessary.

   CAUTION

   Do not use the “Test Connection” link for the Reverse Replication Outbox on a Publish instance.

   If a replication test is performed for an Outbox queue, any items that are older than the test replication are reprocessed with every reverse replication.

   If such items exist in a queue, they can be found with the following XPath JCR query and should be removed.

   /jcr:root/var/replication/outbox//*[@cq:repActionType='TEST']

Batch Replication

The batch replication does not replicate individual pages or assets, but waits for the fist threshold of the two, based on time or size, to be triggered.

It then packs all replication items into a package, which is then replicated as one single file to the Publisher.

The Publisher unpacks all the items, save them and report back to the Author.

Configuring Batch Replication

1. Go to http://serveraddress:serverport/siteadmin
2. Press the Tools icon in the upper-side of the screen
3. From the left-hand side navigation rail, go to Replication - Agents on Author and double-click Default Agent.
   • You can also reach the default Publish replication agent by going directly to http://serveraddress:serverport/etc/replication/agents.author/publish.html
4. Press the Edit button above the replication queue.
5. In the following window, go to the Batch tab:
   
6. Configure the agent.

Parameters

• Enable Batch Mode - enables or disables batch replication mode
• Max Wait Time - Maximum wait time until a batch request is started, in seconds. The default is 2 seconds.
• Trigger Size - Starts batch replication when this size limit

Additional Resources

For details about troubleshooting, you can read the Troubleshooting Replication page.