Node Manager

As the name suggests, Node Manager runs on each of the Hadoop slave nodes participating in the cluster. This means that there could many Node Managers present in a cluster when that cluster is running with several nodes. The following diagram depicts key functions performed by Node Manager:

Node Manager runs different services to determine and share the health of the node. If any services fail to run on a node, Node Manager marks it as unhealthy and reports it back to resource manager. In addition to managing the life cycles of nodes, it also looks at available resources, which include memory and CPU. On startup, Node Manager registers itself to resource manager and sends information about resource availability. One of the key responsibilities of Node Manager is to manage containers running on a node through its Container Manager. These activities involve starting a new container when a request is received from Application Master and logging the operations performed on container. It also keeps tabs on the health of the node.

Application Master is responsible for running one single application. It is initiated based on the new application submitted to a Hadoop cluster. When a request to execute an application is received, it demands container availability from resource manager to execute a specific program. Application Master is aware of execution logic and it is usually specific for frameworks. For example, Apache Hadoop MapReduce has its own implementation of Application Master.

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Node Manager