rabbit_peer_discovery: Cache computed node start time #13128
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[Why] The computation of a node's system-time-based start time is based on its monotonic-time-based start time plus the current time offset. However, since Erlang/OTP 26, that time offset is volatile by default. Therefore the computed system-time-based start time can change too. It happens in CI and this affects the seed node selection in the peer discovery code: because the sorting is unstable when the start time is the criteria, different instances of the peen discovery code could select a different node. [How] The same code is used to compute the start time. However, the computed value is cached in a persistent_term for future queries. This way we ensure that the value is computed once and thus all queries will return the same result.
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Why
The computation of a node's system-time-based start time is based on its monotonic-time-based start time plus the current time offset.
However, since Erlang/OTP 26, that time offset is volatile by default. Therefore the computed system-time-based start time can change too. It happens in CI and this affects the seed node selection in the peer discovery code: because the sorting is unstable when the start time is the criteria, different instances of the peen discovery code could select a different node.
How
The same code is used to compute the start time. However, the computed value is cached in a persistent_term for future queries. This way we ensure that the value is computed once and thus all queries will return the same result.