Context Propagation in opentelemetry-go-auto-instrumentation is inspired
by Apache-Skywalking.
Context in OpenTelemetry is a design for propagating trace-related information in distributed systems. Based on the
propagation of Context, distributed services (AKA Spans) can be linked together to form a complete call chain (AKA
Trace). OpenTelemetry saves trace-related information in Golang's context.Context and requires users to correctly pass
context.Context. If context.Context is not passed correctly in the call chain, the call chain will be broken. To solve
this problem, when opentelemetry-go-auto-instrumentation create a span, opentelemetry-go-auto-instrumentation save
it to Golang's coroutine structure (i.e. GLS), and when opentelemetry-go-auto-instrumentation create a new
coroutine, opentelemetry-go-auto-instrumentation also copy the corresponding data structure from the current
coroutine. When opentelemetry-go-auto-instrumentation need to create a new span
later, opentelemetry-go-auto-instrumentation will query the most recently created span from GLS as the parent, so that
opentelemetry-go-auto-instrumentation have the opportunity to protect
the integrity of the call chain.
Baggage is a data structure in OpenTelemetry used to share key-value pairs in Trace. Baggage is stored in
context.Context and is propagated along with the context.Context. If context.Context is not correctly propagated in the
call chain, subsequent services will not be able to read Baggage. To solve this problem,
when opentelemetry-go-auto-instrumentation save the baggage to
context.Context, opentelemetry-go-auto-instrumentation also save it to GLS. When context.Context is not passed
correctly, opentelemetry-go-auto-instrumentation try to read the baggage from
GLS, which allows the baggage to be read in this case.