Safe per tenant overrides loading #4421
Merged
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Historically, the
Limits
used to use pass-by-value semantics to clone themselves during per tenant overrides loading. This worked well when theLimits
struct had no reference fields (pointers, slices, maps). Adding them, notablyruler_remote_write_headers
,ruler_remote_write_relabel_configs
, andretention_stream
introduced some mutability bugs. Notably, this allowed loading per tenant overrides to mutate the global defaults, which would then be used in subsequent tenant overrides creation. This PR fixes this loophole by introducing a marshaling cycle as a cloning hack.