Monitoring multiple servers or instances of a server

An agent can monitor multiple servers, including multiple instances of the same server. There are two ways of creating such agents: multiple instances of an agent and subnodes within an agent.

Multiple instances are a standard way to monitor application servers that can have a number of similar instances on the same host. Many standard agents in IBM® Tivoli® Monitoring and IBM Cloud Application Performance Management support multiple instances.

With multiple instances, you install an agent on a monitored hosts and then configure one or several instances, setting a name for every instance. Configure an instance of the agent for each instance of the server that you want to monitor. Each instance is a separate identical copy of the agent, and it can be started and stopped separately.

You can also define one or several types of subnode within an agent. Each type must correspond to a different type of resource that an agent can monitor. A subnode type contains data sources and data sets; you can also define data sources and data sets at agent level, outside any subnode. When you install the agent on a host, you can configure the required number of subnodes of each type; for every subnode type, you can set the number of subnodes independently. For IBM Cloud Application Performance Management, you can create a dashboard for the agent and a separate dashboard for each subnode.

Subnodes require different configuration steps on the monitored host. Also, to reconfigure, add or remove a subnode. you must stop and restart the entire agent; an instance can be reconfigured, added, or removed without affecting other instances. However, subnodes have a number of advantages:

With subnodes, you can monitor a large amount of server instances while consuming less resources. As a guideline, the number of agent instances of a specific type supported on a single system is 10. But an agent can monitor up to 100 local or remote servers using subnodes.
One agent can include subnode types for a few different kinds of servers. On the monitored system, you can configure any number of subnodes of each type. You can use this feature to conserve resources further.
An agent with subnodes can supply system-wide data on the agent level.

You can define both multiple instances and subnodes for the same agent. In this case, each instance can include a number of subnodes. You can stop and restart each instance independently of other instances; all subnodes in an instance are stopped and restarted together.