Consensus and Raft
On This Lesson 4 topics
This lesson is planned. The outline below lists the topics it will cover. The full lesson has not been published yet.
In this lesson
explain Raft well enough to judge systems that rely on it.
Planned topics
- Consensus makes a group agree on one ordered log despite failures.
- Raft: leader election by term, log replication, commit when a majority has the entry.
- A majority (quorum) is needed, so 3 nodes tolerate 1 failure, 5 tolerate 2.
- Without a majority the system stops accepting writes rather than diverge; that is a choice for consistency.
Draft outline details
Demonstration
a timeline of a 3-node cluster: leader N1 fails, N2 times out, requests votes in term 2, wins with N3, continues the log; a diagram of an entry committed once on 2 of 3 nodes.
Check your understanding
How many failures does a 5-node Raft group tolerate?
Show answer
Two, since a majority of three must remain.
Practice
Apply this lesson with the module's lab, exercises and quiz.
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