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45ccceb137
Before this patch, the "/localnodes" HTTP request to the Alternator server
lists all the live nodes of the current DC. This patch adds two optional
parameters to this query:
dc: allows to list the live nodes of a specific named DC instead of the
current DC of the server.
rack: allows to restrict the results to just the nodes belonging to a
specific named rack.
For both options, if no live node exists in the given dc or rack (in
particular, if such a dc or rack doesn't even exist), an empty list is
returned - it's not an error.
The default, if dc or rack is not specified - remains exactly as it is
today - look at the current DC (the one of the node being request), and
do not restrict the list to any specific rack.
We expect the new options that we added here to be useful for two use cases:
1. A client that knows of *some* Scylla node (belonging to an unknown DC),
but wants to list the nodes in *its* DC, which it knows by name.
2. A client in a multi-rack DC (e.g., multi-AZ region in AWS) that wants
to send requests to nodes in its own rack (which it knows by name),
to avoid cross-rack networking costs.
Note that in both cases, this requires clients to know the names of DCs
and AZs via some out-of-band means. The client can also get a list of DCs
and racks using the system.local system table, as the tests included in
this patch demonstrate.
This patch includes two set of tests for these new options: One in the the
single-node test/alternator framework that has a single dc and rack but
can still check the case of an unknown dc or rack (in which case an empty
list is returned). The second test is in the topology framework, and runs
an 8-node cluster with two DCs, two racks, and two nodes in each, and
checks all the combinations of "/localnodes" requests with and without
dc and rack options. This test also resolves a longstanding TODO that
asked for such a multi-DC test for "/localnodes" to be written.
Fixes #12147
Signed-off-by: Nadav Har'El <nyh@scylladb.com>
Closes scylladb/scylladb#20915