Allow us to inject annotations into children trace contexts. Example, with dark
traffic or retries we want to be able to tag the produced spans from each call
(the light/dark calls, or each individual retry) with information that allows us
to tie them together as a single logical item: a light request paired with a dark
request, or an initial request and a series of retries. The problem lies in the fact
that at the time we have the information about the relationship, the
child trace context doesn't actually yet exist. In order to trace where it is needed, we need
to have a hook into the trace context of these children requests which don't yet exist.
We do this by placing annotations we want each child trace context to carry inside the local
context and accessing them when the child trace context is realized through a stack module. The
stack module will place a filter in the correct trace context, after the Trace Initialization
Filter, which allows us to record the annotations in the proper place.
Allow us to inject annotations into children trace contexts. Example, with dark traffic or retries we want to be able to tag the produced spans from each call (the light/dark calls, or each individual retry) with information that allows us to tie them together as a single logical item: a light request paired with a dark request, or an initial request and a series of retries. The problem lies in the fact that at the time we have the information about the relationship, the child trace context doesn't actually yet exist. In order to trace where it is needed, we need to have a hook into the trace context of these children requests which don't yet exist. We do this by placing annotations we want each child trace context to carry inside the local context and accessing them when the child trace context is realized through a stack module. The stack module will place a filter in the correct trace context, after the Trace Initialization Filter, which allows us to record the annotations in the proper place.