Secondary Publishing Agents
A secondary Publishing Agent is added to a Site for redundancy. This way if the master Publishing Agent fails, the secondary Publishing Agent is still available to handle the requests. Publishing Agents work in active/active manner to ensure high availability. In case of a Publishing Agent failure, the next agent is always ready to handle the load. In general, the N+1 redundancy approach should be used per Site. Note that for auto-promotion you shouldn't have more than three Publishing Agents (auto-promotion is described later in this section).
When you have one more secondary Publishing Agents installed, the runtime data is replicated on each agent, so if any service fails, the downtime is reduced to a minimum. In addition, any active Publishing Agent is used for authentication purposes with both the AD and any 2nd level authentication provider used.
The master Publishing Agent performs the same tasks as secondary Publishing Agents but has additional responsibilities. It manages certain processes that must be managed by a single Publishing Agent. The following table lists processes managed by the master Publishing Agent and secondary Publishing Agents:
As a demonstration of how load distribution between multiple Publishing Agents works, consider the following example:
The resulting load will be distributed as follows:
Planning for secondary Publishing Agents
RAS Publishing Agents running on the same Site communicate with each other and share the load. The amount of data being transmitted from one agent to another is quite large, so a reliable high-speed communication channel must be ensured (e.g. a subnetwork can be configured for Publishing Agent communications).
When adding a secondary Publishing Agent to a Site, you specify an IP address for it. Make sure that the IP addresses of all agents belong to the same network segment. The port that Publishing Agents use to communicate with each other is TCP 20030.
There's no physical limit to how many Publishing Agents you can add to a Site. However, the best results are achieved with only two-three agents present. The three-agent scenario is highly recommended, especially when you have VDI providers and want to enable high availability for VDI. Adding more than two secondary Publishing Agents to a Site may have a reverse effect and actually degrade the system performance. Note that this does not apply to secondary Publishing Agents in standby mode, which is explained in Configuring RAS Publishing Agents.
Adding a secondary RAS Publishing Agent to a Site
To add a secondary Publishing Agent: