change config file to manage composition

[atoulme]

BREAKING CHANGE: To facilitate the composability of configuration needed in system packages, the configuration now moves under /etc/opentelemetry/injector/, with the main configuration file a /etc/opentelemetry/injector/injector.conf, merging with drop-in files under /etc/opentelemetry/injector/conf.d/.

The environment variable configuration file also moves from /etc/opentelemetry/default_auto_instrumentation_env.conf to /etc/opentelemetry/injector/default_env.conf.

The default auto-instrumentation agent paths are now empty. Paths are provided by per-language conf.d drop-in files installed by the respective language packages (e.g., opentelemetry-java-autoinstrumentation installs jvm.conf).

Users building custom container images must now explicitly configure the agent paths via conf.d files, the main configuration file, or environment variables.

This change has been extracted from #239.

[linux-foundation-easycla]

The committers listed above are authorized under a signed CLA.

• ✅ login: atoulme / name: Antoine Toulme (9d752e2, a1d49bf)
• ✅ login: mmanciop / name: Michele (556e623, 84604f7, e5fd8da, ec4b26f)

[mmanciop]

I would prefer to avoid breaking changes like this, which likely will go unnoticed by users and will just result in apps not instrumenting (so, almost a silent failure)

Agreed in the SIG to this being a breaking change

[basti1302]

non-blocking: We could maybe improve this a bit to give clear upgrade instructions:

Suggested change

	The default auto-instrumentation agent paths are now empty. Paths are provided by per-language conf.d drop-in files
	installed by the respective language packages (e.g., `opentelemetry-java-autoinstrumentation` installs `java.conf`).
	Users building custom container images must now explicitly configure the agent paths via conf.d files, the main
	configuration file, or environment variables.
	Breaking change: On systems where custom settings have been configured in `/etc/opentelemetry/otelinject.conf`, these need to move to one of the new locations, for example `/etc/opentelemetry/injector/otelinject.conf`.
	Breaking change: The in-code defaults for the auto-instrumentation agent paths are now empty. Paths must be provided via external configuration. Users who use the injector binary directly, but do not use the system packages published by this project, and who also have previously relied on the default auto-instrumentation agent paths must now explicitly configure the agent paths. This can be done either via the main configuration file (default: `/etc/opentelemetry/injector/otelinject.conf`), or conf.d-style files in the configuration directory (e.g. files under `/etc/opentelemetry/injector.d`), or via environment variables.

We should discuss #291 (comment) first though

[mmanciop]

Taken a stab at this in e5fd8da

[atoulme]

+1 on Basti’s suggestion

[mmanciop]

So we now have two directories under /etc/opentelemetry, one is called injector and one is called injector.d. Is this idiomatic for a conf.d style approach?

Well, yes. See /etc/sudoers vs /etd/sudoers.d. However, tbh both the "sibling" approach like I implement, and the nested one that Basti proposes are both widespread.

I could even see how rename conf.d to something like injected-sdks.d or so, to better set expectations about what goes in that folder:

/etc/opentelemetry/injector/
├── injector.conf          ← main configuration file
├── default_env.conf
└── injected-sdks.d/       ← drop-in directory
    ├── 00-java.conf
    ├── 10-nodejs.conf
    └── 99-whatever.conf

[basti1302]

Well, yes. See /etc/sudoers vs /etd/sudoers.d.

But /etc/sudoers is the main config file and its sibling /etd/sudoers.d the drop-in directory, right? This is different from what the PR currently does. I have not come across any wide-spread use of two sibling directories like we have here, /etc/opentelemetry/injector and /etc/opentelemetry/injector.d, which are both directories.

The current structure would look like this:

/etc/opentelemetry/injector/
├── injector.conf 
├── default_env.conf

/etc/opentelemetry/injector.d/
├── 00-java.conf
├── 10-nodejs.conf
└── 99-whatever.conf

I think the /etc/sudoers plus /etd/sudoers.d is not a good fit for us because we have two default files, the main config file and default_env.conf.

[basti1302]

/etc/opentelemetry/injector/
├── injector.conf          ← main configuration file
├── default_env.conf
└── injected-sdks.d/       ← drop-in directory
    ├── 00-java.conf
    ├── 10-nodejs.conf
    └── 99-whatever.conf

That works for me. I would slightly prefer to not be over-specific with the name injected-sdks.d/ and use a generic name, because we cannot foresee all possible use cases for this directory. But I'm fine with both.

[mmanciop]

/etc/opentelemetry/injector/
├── injector.conf          ← main configuration file
├── default_env.conf
└── injected-sdks.d/       ← drop-in directory
    ├── 00-java.conf
    ├── 10-nodejs.conf
    └── 99-whatever.conf

That works for me. I would slightly prefer to not be over-specific with the name injected-sdks.d/ and use a generic name, because we cannot foresee all possible use cases for this directory. But I'm fine with both.

Alright, then /etc/opentelemetry/injector/conf.d it is. We likely do not have enough clarity about the configurations to go as semantic as I proposed.

[basti1302]

👍