Populate zone attribute from COUCHDB_ZONE environment variable #5588
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willholley
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rnewson
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src/couch/src/couch_util.erl
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| Value :: any(), | ||
| TupleList2 :: [Tuple]. | ||
| set_value(Key, TupleList1, Value) -> | ||
| TupleList2 = [{Key, Value} | TupleList1], |
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nickva
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nickva
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couch_util:set_value/3 previously only worked when replacing a value associated with an existing key. This commit changes the semantics to be "set or update". I've also added a typespec for completeness.
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+1
Thanks for also updating the docs
big-r81
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big-r81
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This adds a feature to populate the zone field in the `nodes` database by setting the `COUCHDB_ZONE` environment variable. The zone is used in combination with [placement](https://docs.couchdb.org/en/stable/cluster/databases.html#placing-a-database-on-specific-nodes) rules to specify that database shard replicas must exist across specific nodes - most commonly used to specify that a replica should exist in multiple availability zones in a region. Setting the zone was previously an awkward piece of cluster setup orchestration because it required editing the node document in the local "nodes" database before creating any system databases. This instead sets the zone when initially creating the node document on startup, which should then get replicated to other peers in the cluster. One nuance is that multiple nodes in the cluster might create the same first revision of the node document due to the seedlist feature. To prevent conflicts when the nodes database is replicated internally, the zone is set using an additional update to the document associated with the current node only.
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Overview
This adds a feature to populate the zone field in the
nodesdatabase by setting theCOUCHDB_ZONEenvironment variable. Setting the zone for a node was previously an awkward piece of cluster setup orchestration because it required editing the a document on each of the local "nodes" after CouchDB has started but before creating any other system databases.This implementation reads the
COUCHDB_ZONEenvironment variable when mem3 starts and, if present, updates the local node document with that zone string.One nuance is that multiple nodes in the cluster might create the same first revision of a node document due to the seedlist feature, which pre-emptively adds the seeds to the nodes database. To prevent conflicts when the nodes database is replicated between peers, the zone is set using an additional update to the node document for the local node only.
Other things to note:
COUCHDB_ZONEto change in the lifetime of a node, but the code does allow this.COUCHDB_ZONEis not set, no modifications to the node document are made.Testing recommendations
Eunit tests are added to verify the node document is as expected. You can also test using:
Related Issues or Pull Requests
Checklist
rel/overlay/etc/default.inisrc/docsfolder