TraceId 和 SpanId 在 WebFilter 中是 null，即使它是在 TraceWebFilter 之后注册的

Question

I'm currently using 2020.0.0 with Spring Boot 2.4.2 and registered a custom web filter that logs information from the request (Order is webProperties.filterOrder + 1 -- so it should be registered after TraceWebFilter). For some reason, traceId and spanId are not in MDC (and therefore not logging).

WebFilter implementation:

class TraceWebFilter(
        private val webProperties: SleuthWebProperties,
        private val tracer: Tracer
): WebFilter, Ordered {
    override fun getOrder(): Int = webProperties.filterOrder + 1

    override fun filter(exchange: ServerWebExchange, chain: WebFilterChain): Mono<Void> {
        logger.debug { "Building trace web filter" }

        return Mono.defer {
            MDC.put("Request-Method", exchange.request.method?.toString())
            MDC.put("Request-Path", exchange.request.path.toString())

            logger.info { tracer.currentSpan() }

            logger.info { ">> headers=${exchange.request.headers}" }
            logger.info { ">> method=${exchange.request.method}" }
            logger.info { ">> path=${exchange.request.path}" }

            exchange.response.beforeCommit {
                Mono.fromRunnable {
                    logger.info { "<< headers=${exchange.response.headers}" }
                    logger.info { "<< status=${exchange.response.rawStatusCode}" }
                }
            }

            chain.filter(exchange)
        }
    }
}

Logs:

app_1       | 2021-01-28 04:43:24.420 DEBUG [user-service,method=,path=,traceId=,spanId=] 1 --- [p-nio-80-exec-2] o.s.c.s.instrument.web.TraceWebFilter    : Received a request to uri [/users]
app_1       | 2021-01-28 04:43:24.566 DEBUG [user-service,method=,path=,traceId=,spanId=] 1 --- [p-nio-80-exec-2] o.s.c.s.instrument.web.TraceWebFilter    : Handled receive of span RealSpan(9b7383611e5a3bc2/9b7383611e5a3bc2)
app_1       | 2021-01-28 04:43:24.633 DEBUG [user-service,method=,path=,traceId=,spanId=] 1 --- [p-nio-80-exec-2] c.p.p.components.tracing.TraceWebFilter  : Building trace web filter
app_1       | 2021-01-28 04:43:24.638  INFO [user-service,method=POST,path=/users,traceId=,spanId=] 1 --- [p-nio-80-exec-2] c.p.p.components.tracing.TraceWebFilter  : null
app_1       | 2021-01-28 04:43:24.694  INFO [user-service,method=POST,path=/users,traceId=,spanId=] 1 --- [p-nio-80-exec-2] c.p.p.components.tracing.TraceWebFilter  : >> headers=[content-type:"application/json", user-agent:"PostmanRuntime/7.26.8", accept:"*/*", cache-control:"no-cache", postman-token:"18d99e30-ce7a-4659-a2c1-21020d8bf2b5", host:"localhost:9100", accept-encoding:"gzip, deflate, br", connection:"keep-alive", content-length:"2"]
app_1       | 2021-01-28 04:43:24.699  INFO [user-service,method=POST,path=/users,traceId=,spanId=] 1 --- [p-nio-80-exec-2] c.p.p.components.tracing.TraceWebFilter  : >> method=POST
app_1       | 2021-01-28 04:43:24.747  INFO [user-service,method=POST,path=/users,traceId=,spanId=] 1 --- [p-nio-80-exec-2] c.p.p.components.tracing.TraceWebFilter  : >> path=/users

Please notice the following:

• traceId and spanId in the logs are null
• logged tracer.currentSpan in logs is null

Any clues as to why this is happening?

Answer 1

If you look at TraceWebFilter , you will see that it does not put anything into the MDC ( MDC is basically a ThreadLocal and you are in an async event loop).

1. But it interacts with the Tracer that you can also inject into your filter and get the current Span from it: tracer.currentSpan() and from the TraceContext of the Span you can get the traceId and spanId .

2. Also, it puts the Span into the Exchange Attributes:

this.exchange.getAttributes().put(TRACE_REQUEST_ATTR, span);

I recommend injecting the Tracer into your filter and getting the current Span from it.