From c6dd7cdcee0ff848d2f135e7dd841050736c23c4 Mon Sep 17 00:00:00 2001 From: Philip O'Toole Date: Thu, 29 Apr 2021 23:32:37 -0400 Subject: [PATCH] Update CHANGELOG.md --- CHANGELOG.md | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) diff --git a/CHANGELOG.md b/CHANGELOG.md index 608cfc8b..c6ee7673 100644 --- a/CHANGELOG.md +++ b/CHANGELOG.md @@ -1,9 +1,9 @@ ## 6.0.0 (unreleased) -This release implements a significant design change, which improves rqlite cluster reliability. +This release implements a significant design change, which improves rqlite cluster reliability. With this change a rqlite node can more reliably direct read and write requests to the correct node. -In the 5.0 series, _Follower_ nodes learned the HTTP API address of a cluster Leader via information - known as _Metadata_ - that each node wrote to the Raft log. This Metadata was then available to each node in the cluster, if that node needed to redirect queries to the cluster Leader (assuming that node wasn't the Leader at that time). However that design was somewhat complex, and required the tracking of state, in addition to the SQLite database. It also meant that if the Metadata got out of sync with the Raft state, the cluster could be in a degraded state. +In the 5.0 series, _Follower_ nodes learned the HTTP API address of the cluster Leader via information - known as _Metadata_ - that each node wrote to the Raft log. This Metadata was then available to each node in the cluster, if that node needed to redirect queries to the cluster Leader (assuming that node wasn't the Leader at that time). However that design was somewhat complex, and required the tracking of extra state, in addition to the SQLite database. It also meant that if the Metadata got out of sync with the Raft state, the cluster could be in a degraded state. -In this new design, a node now queries the Leader as needed, when that node needs to learn the Leader's HTTP API address. As a result, the Metadata component has been removed from rqlite. And without any possibility of discrepancy between Metadata and Raft state, a whole class of potential bugs is removed. Any request for the Leader HTTP API address means a node connects to the TCP port already open (and required) for Raft connections, so does not introduce any new failure modes. This multiplexing of the Raft connection is performed via the `mux` package. +In this new design, a node now queries the Leader as needed, when that node needs to learn the Leader's HTTP API address. As a result, the Metadata component has been removed from rqlite, since it is no longer needed. And without any possibility of discrepancy between Metadata and Raft state, a whole class of potential bugs is removed. Any request for the Leader HTTP API address means a node connects to the TCP port already open (and required) for Raft connections, so does not introduce any new failure modes. This multiplexing of the Raft connection is performed via the `mux` package. This new design does mean that nodes running earlier software cannot communicate with 6.0 nodes, as 6.0 software no longer performs Metadata updates. As a result, **rqlite clusters running 5.x software or earlier must be explicitly upgraded**. To upgrade from an earlier version to this release you should [backup your Leader node](https://github.com/rqlite/rqlite/blob/master/DOC/BACKUPS.md), and [restore the database dump](https://github.com/rqlite/rqlite/blob/master/DOC/RESTORE_FROM_SQLITE.md) into a new 6.0 cluster.