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During a node's startup, a lot of required services are automatically started. The most important ones are as follows:

• Cluster services: This helps you manage the cluster state and intranode communication and synchronization
• Indexing service: This helps you manage all the index operations, initializing all active indices and shards
• Mapping service: This helps you manage the document types stored in the cluster (we'll discuss mapping in Chapter 2, Managing Mapping)
• Network services: This includes services such as HTTP REST services (default on port 9200), and internal Elasticsearch protocol (port 9300) if the thrift plugin is installed
• Plugin service: This manages loading the plugin 
• Aggregation services: This provides advanced analytics on stored Elasticsearch documents such as statistics, histograms, and document grouping
• Ingesting services: This provides support for document preprocessing before ingestion such as field enrichment, NLP processing, types conversion, and automatic field population
• Language scripting services: This allows you to add new language scripting support to Elasticsearch