Expected Behavior

The serving branch has moved to structured logging and this issue is tracking the move of build code to structured logging as well. Below is a proposed guideline by @grantr to determine if something should be kept in the log message vs should be a separate key/value pair in the logs:

If a field can act as a filter key to group messages, it should be a structured log field. If a field's searchability will lead to confusion (for example, if it tends to be parsed incorrectly or is easily confused with a different field) then it should not be a structured log field. If a field's key is dynamic with high cardinality, then it should be interpolated (though in this case, the dynamic key should likely be a value itself).