Project: SkyWalking (Observability and Analysis / Observability)
File: probe-introduction.md

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 four 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 `-javaagent` command line argument to manipulate codes in runtime, where `manipulate` means to change and inject user's codes. Another example is SkyWalking agent, which leverage Golang compiling mechanism to weaves codes in the compiling time. For some static compilation languages, such as C++, manual library is the only choice. As you can see, these agents are based on languages and libraries, no matter we provide auto instrument or manual agents. Service Mesh probes. Service Mesh probes collect data from sidecar, control plane 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. SkyWalking community is connected closely with Zipkin community, it could work as an alternative server for both v1 and v2 Zipkin traces. Also, OTEL trace format in gRPC is supported, and converted to Zipkin format inside SkyWalking. As an alternative Zipkin server, Zipkin lens UI could be used to visualize accepted traces when they are in Zipkin format. See and for more information. eBPF agent. The eBPF agent collects metrics and profiling the target service powered by the eBPF technology of Linux kernel. You don't have to install all probes to make SkyWalking up and running. There are several recommended ways on how to use these probes: Use Language based native agent only to build topology and metrics for your business application. Use 3rd-party instrument library only, like the Zipkin instrument ecosystem. Use Service Mesh probe if you prefer Service Mesh stack and don't want to use native agents. Use Service Mesh probe with Language based native agent or 3rd-party instrument library in pure tracing status. (Advanced usage) Use eBPF agent only if you only want to profile on demand and/or activating automatic performance analysis. Use eBPF agent with Language based native agent collaboratively. Enhance the traces with the eBPF agent to collect extra information. 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 pure tracing status means that the backend considers these traces as something like logs. In other words, the backend saves them, but doesn't run the metrics analysis from traces. As a result, there would not have data of `service/instance/endpoint metrics and relationships`. Learn more about the probes supported by SkyWalking in , and . After understanding how the probe works, see the for more on analysis and persistence.