In SkyWalking, probe means an agent or SDK library integrated into a target system that takes charge of collecting telemetry data, including tracing and metrics. Depending on the target system tech stack, there are very different ways how the probe performs such tasks. But ultimately, they all work towards the same goal — to collect and reformat data, and then to send them to the backend.
On a high level, there are three typical categories in all SkyWalking probes.
Language based native agent. These agents run in target service user spaces, such as a part of user codes. For example, the SkyWalking Java agent uses the
-javaagentcommand line argument to manipulate codes in runtime, where
manipulatemeans to change and inject user’s codes. Another kind of agents uses certain hook or intercept mechanism provided by target libraries. As you can see, these agents are based on languages and libraries.
Service Mesh probes. Service Mesh probes collect data from sidecar, control panel in service mesh or proxy. In the old days, proxy is only used as an ingress of the whole cluster, but with the Service Mesh and sidecar, we can now perform observability functions.
3rd-party instrument library. SkyWalking accepts many widely used instrument libraries data formats. It analyzes the data, transfers it to SkyWalking’s formats of trace, metrics or both. This feature starts with accepting Zipkin span data. See Receiver for Zipkin traces for more information.
You don’t need to use Language based native agent and Service Mesh probe at the same time, since they both serve to collect metrics data. Otherwise, your system will suffer twice the payload, and the analytic numbers will be doubled.
There are several recommended ways on how to use these probes:
- Use Language based native agent only.
- Use 3rd-party instrument library only, like the Zipkin instrument ecosystem.
- Use Service Mesh probe only.
- Use Service Mesh probe with Language based native agent or 3rd-party instrument library in tracing status. (Advanced usage)
What is the meaning of in tracing status?
By default, Language based native agent and 3rd-party instrument library both send distributed traces to the backend,
where analyses and aggregation on those traces are performed. In tracing status means that the backend considers these traces as something
like logs. In other words, the backend saves them, and builds the links between traces and metrics, like
which endpoint and service does the trace belong?.