# 04-mdc-keys  (Spring Boot 4.1.2, JDK 25)
management.tracing.mdc.trace-id-key = trace_id
management.tracing.mdc.span-id-key  = span_id
log pattern correlation part reads both MDC keys

log line: INFO 4192 --- [boot42-otel] [o-auto-1-exec-1] default[<32-hex-trace-id>] custom[] c.a.o.OtelApplication$HelloController    : handling hello for ankur
default key traceId populated: true
custom key trace_id populated: false