Primary node
A primary node is a designated authoritative or coordinating member of a distributed system, typically responsible for accepting operations or coordinating replicated state.
Apache Kafka in Action
A Kafka partition leader is the broker responsible for handling reads and writes for a partition.
- How it is used
- Identifies the broker responsible for a partition’s reads and writes in a replicated Kafka cluster.
- How deep it goes
- Explains leader–follower replication, metadata discovery, and acknowledgment choices; leaves detailed broker storage mechanics outside the leader definition.
- Examples
- Uses a bank-transfer topic and `kafka-topics.sh --describe` output showing leaders on three different brokers.
- What you can do after
- Diagnose/debug with it by locating a partition leader, checking in-sync replicas, and relating producer acknowledgment settings to failure risk.
MongoDB 8.0 in Action, Third Edition
A primary member is the replica set member that accepts write operations and coordinates replication.
- How it is used
- Identifies the replica set member responsible for writes and the starting point of replication to secondaries.
- How deep it goes
- Explains member states and the primary-to-secondary oplog flow, with shell commands for inspection rather than primary configuration steps.
- Examples
- Uses replica set status and configuration output alongside oplog entries for session deletions and inserts.
- What you can do after
- Operate/configure it by identifying the primary with mongosh status commands and checking member settings where supported.
Read how MongoDB 8.0 in Action, Third Edition explains primary node →
Kafka for Architects
A Kafka partition leader is the replica that coordinates writes for that partition and serves as the synchronization reference for follower replicas.
- How it is used
- Defines the replica that receives producer writes and supplies new data to followers for a Kafka partition.
- How deep it goes
- Explains replica placement, asynchronous replication, in-sync replicas, and producer rerouting; defers detailed reliability strategies.
- Examples
- Uses a leader-and-follower partition diagram and a producer whose cached leader metadata becomes stale after a leadership change.
- What you can do after
- Diagnose/debug with it when producer sends encounter a former leader or writes fail because too few in-sync replicas are available.
Amazon Web Services in Action, Third Edition: An in-depth guide to AWS
A primary node is the authoritative cache node that accepts data operations and provides the source state for replicas.
- How it is used
- Directs writes and authoritative state while replicas provide redundancy or additional read capacity.
- How deep it goes
- Distinguishes primary, replica, standby, sharding, and failover, but does not detail replication protocols or election internals.
- Examples
- Uses RDS standby promotion, 4 GB single-shard caches, and 22 GB Redis data distributed across six shards.
- What you can do after
- Configure replication or sharding through ElastiCache Redis deployment choices and understand how managed failover redirects clients.
Related concepts
- follower nodecontrasts with · A follower node is a non-primary replica that receives replicated data or state from a leader and generally does not initiate leadership.
- Kafka brokerkind of · A Kafka broker is a server process in an Apache Kafka cluster that stores records and handles producer, consumer, and other client requests.
- replicacontrasts with · A replica is a copy of data or state, or an equivalent running instance of a component, maintained alongside others in a replicated system.
- acknowledgmentproduces · An acknowledgment is a protocol message or signal confirming that transmitted data, a message, request, or operation was received or processed.
- monitoringuses · Monitoring is the ongoing observation and measurement of a system’s behavior, state, or operational signals to assess its condition and detect changes or problems.
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