Zipkin-SkyWalking Exporter supports Apache SkyWalking's collector accept Zipkin trace format. This extends SkyWalking to the OpenZipkin ecosystem, by allowing existing applications to send data to SkyWalking. We accomplish this by mapping the spans to SkyWalking Trace Data Protocol
Note: currently an trace can only include data from SkyWalking agents or Zipkin instrumentation, but not both. W3C distributed-tracing specification may help some day, still need further discussion.
- Zipkin v2: https://zipkin.io/zipkin-api/#/default/post_spans
- SkyWalking 5.x: SkyWalking Trace Data Protocol
5.x
A set of spans that share a single root span. TraceId maps the GlobalTraceId in SkyWalking.
No TraceSegment concept in Zipkin. Require Trace and TraceSegment Rebuid mechanism.
In SkyWalking, Span is just a concept, not real. There are three sub-concept, and real classes are EntrySpan, LocalSpan and ExitSpan.
LocalSpan and ExitSpan relate RPC and MQ, mapping Zipkin's Span with RemoteEndpoint.
All these three IDs are String in Zipkin, and format is
maxLength: 32
minLength: 16
pattern: [a-z0-9]{16,32}
In SkyWalking, TraceId is a combination by three Integers. SpanId and ParentSpanId are small Integers, start with 0 in each TraceSegment. There two IDs need to be generated in Trace and TraceSegment Rebuid process.
Epoch microseconds of the start of this span. This equivalent to SkyWalking Span's startTime, but the Unit of SkyWalking is milliseconds.
duration is in microseconds (1 millisecond is 1000 microseconds). SkyWalking has only endTime in milliseconds. So, Zipkin-Span timestamp + duration = SkyWalking-Span endTime.
Application listening address, includes IPv4, IPv6 and port. usually the link local IP.
SkyWalking Mapping: Server identify and InstanceDiscoveryService, including register, heartbeat.
RemoteEndpoint represents the peer network address and service name for a RPC or MQ(broker). In SkyWalking, service name maps ExitSpan's operationName, and ip(v4/v6) + port maps ExitSpan's peer by combining these two as a String with :.
Annotation can be considered as Log in SkyWalking, but no key. So convert it to log with the default log.key=zipkin (Zipkin Annotation).
Tags included in both Zipkin and SkyWalking. And for further analysis and aggregation. Here is the mapping table based on Zipkin core define. Zipkin tags can also include arbitrary data. Conventionally, tag keys longer than 255 characters are not indexed.
| Data required by SkyWalking | Possible Keys in Zipkin |
|---|---|
| Error occurs in this Span scope. | error |
| Componenet library name. e.g. Feign, Resttemplate | lc |
| Layer of this Span. e.g. Database, RPCFramework, Http, MQ, Cache | Presume non, must be conjectured by Component library name or other tags |
| SQL statement | sql.query |
| Database Type | |
| HTTP URL | http.url |
| HTTP Status Code | http.status_code |
| HTTP method | http.method |
| MQ topic/queue name | No |
SkyWalking analysis traces by trace segment, not span. So the rebuild process is about to buffer the upload spans, rebuild them into several segments, based on a trace segment rebuild timeout threshold.
- Rationale of timeout threshold: No one can tell when, where and how a trace end, even for a same service, it changes time to time, because codes upgrade, different parameter or status data. And also this is why SkyWalking use a complex HEAD/SegmentRef to allow analysis and aggregation program didn't expect a full trace to analysis. However, this is impossible for rebuilding process.
+-------------------------------+ +-------------------------------+ +-------------------------------+
| Application under Zipkin trace| | Zipkin-SkyWalking Rebuilder | | SkyWalking Collector |
+-------------------------------+ +-------------------------------+ +-------------------------------+
| /Spans (Zipkin v2) | |
+----------------------------> 1. Rebuild segment |
with same traceid and applicationCode(Requirement¹) |
2. Buffer unfinished segment |
into files |
| SkyWalking gRPC services |
+------------------------------------> Analysis and Aggregation
An additional Tag, key is app.code. Every application under traced should be an explicit application code, in order to show in SkyWalking Topology, Application list etc.