In-depth explanation of Apache SkyWalking inter-process propagation protocol.

Apache SkyWalking is an open-source application performance monitoring system designed to track, monitor, and diagnose performance issues in distributed systems. It utilizes a protocol called Cross-Process Propagation Protocol (CPP) to enable distributed tracing.

The cross-process propagation protocol is a protocol used by SkyWalking to propagate tracking information in distributed systems. Its goal is to pass tracking context between different services so that requests and responses can be correctly associated and a complete call chain can be built.

The main components of the inter-process communication protocol include:

1. Trace ID: A unique identifier used to track a request throughout the system, generated when a request enters the system and passed along through the entire processing process.
2. Span ID (Span Identifier): Used to identify a span or a node within a call chain. Each node has a unique Span ID, allowing it to be associated with its parent and child nodes.
3. Parent Span ID: Used to link a node to its parent node. After a node is processed, its Span ID will be set as the parent node’s Parent Span ID in order to add the node to the parent node’s call chain.
4. Sampling Flag: Indicates whether the current tracking is being sampled. Given the high volume of requests in distributed systems, it is not feasible to track every request, so sampling is used to control the amount of tracking.

Using these components, the cross-process propagation protocol can pass tracing information to different services within a distributed system in order to trace the path and performance of requests. Each service, upon receiving a request, will parse the information in the cross-process propagation protocol and use it to construct a call chain.

In summary, Apache SkyWalking’s cross-process propagation protocol is a method for spreading tracing information in distributed systems. By using components like Trace ID, Span ID, Parent Span ID, and sampling flags, it achieves tracking requests and building call chains. Applying this protocol can assist developers in better understanding and optimizing the performance of distributed systems.