Several times over the years we've considered adding tracing
instrumentation to Terraform, since even when running in isolation as a
CLI program it has a "distributed system-like" structure, with lots of
concurrent internal work and also some work delegated to provider plugins
that are essentially temporarily-running microservices.
However, it's always felt a bit overwhelming to do it because much of
Terraform predates the Go context.Context idiom and so it's tough to get
a clean chain of context.Context values all the way down the stack without
disturbing a lot of existing APIs.
This commit aims to just get that process started by establishing how a
context can propagate from "package main" into the command package,
focusing initially on "terraform init" and some other commands that share
some underlying functions with that command.
OpenTelemetry has emerged as a de-facto industry standard and so this uses
its API directly, without any attempt to hide it behind an abstraction.
The OpenTelemetry API is itself already an adapter layer, so we should be
able to swap in any backend that uses comparable concepts. For now we just
discard the tracing reports by default, and allow users to opt in to
delivering traces over OTLP by setting an environment variable when
running Terraform (the environment variable was established in an earlier
commit, so this commit builds on that.)
When tracing collection is enabled, every Terraform CLI run will generate
at least one overall span representing the command that was run. Some
commands might also create child spans, but most currently do not.
This is part of a general effort to move all of Terraform's non-library
package surface under internal in order to reinforce that these are for
internal use within Terraform only.
If you were previously importing packages under this prefix into an
external codebase, you could pin to an earlier release tag as an interim
solution until you've make a plan to achieve the same functionality some
other way.
