Agent schedule instance (Data-Admin-Queue) can be used to disable the agents (Rule-Admin-Queue). The enabled checkbox on schedule instance can help control the agents run.
Please note based on the no of nodes, multiple agent schedule instance gets created until 7.x versions. So each schedule instance represents a node and can be enabled/disabled on its schedule.
On 8.x versions, schedule instances gets created for each nodeType. By default agent rules are mapped to BackgroundProcessing, so enabling/disabling the agent on the schedule instanced influences the run on all nodes of BackgroundProcessing nodeType.
Eg: If you associate your agent to 2 nodeType categories then 2 schedule instances gets created.
Records > SysAdmin > Agents; Click on an agent > Under Nodes tab > We can enable or disable agent on which node to run (The enabled checkbox on schedule instance can help control the agents run.) This way we can restrict multiple agent schedule instances get created on no of nodes.
Point # 3:
In 8.x, by default agent rules are mapped to BackgroundProcessing, so enabling/disabling the agent on the schedule instanced influences the run on all nodes of BackgroundProcessing nodeType.
Let's say my background processing node types are on Node3 and Node4
If I disable on Node4, would it influences the run on all nodes of BackgroundProcessing nodeType including Node3?
Point # 2: Right, Agents-> Nodes tab will have schedule instances based on the nodeType category the agent is associated. (By default agents are associated to BackgroundProcessing nodeType). Eg:- Though you have 3 JVM's with BackgroundProcessing nodeType, you will also see one schedule instance on the nodes tab. (this applies for all 3 nodes).
Point # 3: Considering your example, actually there is no such thing like disable for node4, there is only one schedule instance for backgroundprocessing type and this applies for both node 3 & node 4. To answer your query, if you disable the agent on this schedule, it will disable the agent for both the nodes.
By default, as both node3 & node4 are associated with one nodeType (backgroundProcessing) controlling agent run only one node is not possible on 8.x
But you can include additional nodeType like Custom1 to node3 and change your agent rule category to Custom1 instead of backgroundProcessing, this way a new schedule gets created for custom1 category and since we only have node3 using Custom1 category, we can use this schedule instance to manage the agent run on node3.
Just want to know one final thing: Let's assume that node3 & node4 are associated with one nodeType (backgroundProcessing), I have one Advanced agent scheduled to run for every 1 hour. Would Pega takes care of running Advanced agent at scheduled time on either node3 or node4?