Remote Agent Activation

Remote agent activation allows you to reduce the amount of processing on the Distributor or Subscriber by running the Distribution Agent or Merge Agent on another computer and then activating that agent remotely using Distributed Component Object Model (DCOM).

You can implement remote agent activation on either push or pull subscriptions. With each type of subscription, you need to:

• Indicate where the agent will run in the Push Subscription or Pull Subscription Wizard.
  
  
• Configure DCOM to activate an agent remotely.
  
  
• Configure or create the subscription indicating where the agent should run.

It is recommended that you set up regular push or pull subscriptions before configuring remote agent activation. You are not able to configure remote agent activation on a local computer (for example, when the Subscriber and Distributor reside on the same computer).

Remote agent activation is supported on Microsoft® SQL Server™ 2000 running on Microsoft Windows NT® 4.0 or Windows® 2000, but it is not supported on Windows 98.

Remote Agent Activation and Push Subscriptions

When Distributor and Subscriber servers have a reliable, continuous connection, push subscriptions allow centralized subscription management. Push subscriptions offer an advantage for organizations that want to control who is allowed to subscribe to publications and when. Push subscriptions are also helpful for circumstances in which the Subscriber needs updates sent to them as soon as they occur.

For push subscriptions, the Distribution Agent (used in snapshot replication or transactional replication) or the Merge Agent (used in merge replication) runs on the Distributor; however, the Distributor can become overloaded as the number of push subscriptions increases.

Remote agent activation allows you to offload agent activity to the Subscriber, which reduces the amount of processing on the Distributor. Using DCOM, you can activate the agent remotely and increase the number of push subscriptions the Distributor can handle.

Using DCOM for remote agent activation with push subscriptions, the Distributor first establishes a connection to the Subscriber. After the connection is made, SQL Server Agent on the Distributor uses DCOM to activate the Distribution Agent or the Merge Agent on the Subscriber.

Remote Agent Activation and Pull Subscriptions

Pull subscriptions offer the ability to manage subscription synchronization locally. This is important for:

• Anyone who travels and needs to connect and synchronize data on demand.
  
  
• Remote offices that need to manage subscription synchronization because they do not have a reliable, continuous connection to the Publisher or Distributor.

For pull subscriptions, the Distribution Agent or the Merge Agent runs on the Subscriber. You can reduce processing at the Subscriber by offloading the Distribution Agent or the Merge Agent activity to the Distributor and using DCOM to activate the agent.

Using DCOM for remote agent activation with pull subscriptions, the Subscriber first establishes a connection to the Distributor. After the connection is made, SQL Server Agent on the Subscriber uses DCOM to activate either the Distribution Agent or the Merge Agent on the Distributor.

Subscription Security Requirements

When you create a subscription, the Distribution Agent or the Merge Agent runs under the security context of SQL Server Agent. Using the security context of SQL Server Agent, the Distribution Agent establishes a connection to the Subscriber and to the Distributor, and when required, to the snapshot folder. The Merge Agent establishes a connection to the Subscriber, the Distributor, the Publisher, and when required, to the snapshot folder. You can view the security requirements for a subscription as if SQL Server Agent were making all of the connections.

After an agent is activated on a remote computer, the agent will be run under the security context as configured through DCOM. When you configure DCOM for remote agent activation, you need to enter a user account that will be used to activate either the Distribution Agent or the Merge Agent. It is recommended that you provide a custom account that is the same as the SQL Server Agent account on the original activating computer.

Enabling Remote Agent Activation When Creating Subscriptions

When creating a push subscription or a pull subscription, you enable remote agent activation by specifying where the agent will run. If the Subscriber is the same server as the Distributor, you will not see the option to run the agent at another server in the Push Subscription or Pull Subscription wizards.

Important  After you specify where the agent should run when creating the subscription, synchronization may fail if you specified that the subscription should be synchronized automatically and you have not configured DCOM for the remote agent activation.

Configuring DCOM for Remote Agent Activation

DCOM handles low-level details of network protocols by extending the Component Object Model (COM) to support communication among objects on different computers, a LAN, a WAN, or the Internet. When configuring DCOM, consider the security that is already in place for SQL Server Agent as well as the type of subscriptions that will be used.

For push subscriptions:

• DCOM must be configured on the Subscriber before you change an existing push subscription or create a new push subscription using remote agent activation.
  
  
• You must have administrative privileges on the Subscriber.
  
  
• The SQL Server Agent on the Distributor must be allowed to use DCOM on the Subscriber.
  
  
• An account or security context needs to be specified through DCOM that will allow the Distribution Agent or the Merge Agent to be run on the Subscriber.

For pull subscriptions:

• DCOM must be configured on the Distributor before you change an existing pull subscription or create a new pull subscription using remote agent activation.
  
  
• You must have administrative privileges on the Distributor.
  
  
• The SQL Server Agent on the Subscriber must be allowed to use DCOM on the Distributor.
  
  
• An account or security context needs to be specified through DCOM that will allow the Distribution Agent or the Merge Agent to be run on the Distributor.

To configure DCOM to run the Distribution Agent remotely