otel: trim non-otel configuration from when validating the otel configuration

[mauri870]

Now with the groundwork for the hybrid agent done in #5796 it is possible to have a yaml config file with both beats and otel configuration, for example:

hybrid-agent-config.yml

# normal agent config
filebeat.inputs:
  - type: filestream
    id: filestream-filebeat
    enabled: true
    paths:
      - /tmp/filebeat.log
output.elasticsearch:
  hosts:
    - https://esendpoint
  api_key: api-key
  index: filebeat-index
# and otel config on the same file
receivers:
  filebeatreceiver:
    filebeat:
      inputs:
        - type: filestream
          id: filestream-fbreceiver
          enabled: true
          paths:
            - /tmp/fbreceiver.log
    output:
      otelconsumer:
    logging:
      level: info
      selectors:
        - '*'
    path.home: /tmp
    queue.mem.flush.timeout: 0s
exporters:
  elasticsearch/log:
    endpoints:
      - https://esendpoint
    api_key: api-key
    logs_index: fbreceiver-index
    batcher:
      enabled: true
      flush_timeout: 1s
    mapping:
      mode: bodymap
service:
  pipelines:
    logs:
      receivers:
        - filebeatreceiver
      exporters:
        - elasticsearch/log

When running ./elastic-agent otel validate --config=./hybrid-agent-config.yml I get the following error:

failed to get config: cannot unmarshal the configuration: decoding failed due to the following error(s):

'' has invalid keys: filebeat.inputs, output.elasticsearch

When validating this file, we need to remove any top-level Beats-specific configuration to ensure that only the OpenTelemetry-specific components are validated.

[elasticmachine]

Pinging @elastic/elastic-agent-data-plane (Team:Elastic-Agent-Data-Plane)

[mauri870]

@kaanyalti I updated the description with more details.

Thinking more about this, I think it is a bit more complicated than I initially thought. Looking at the otel configuration docs there are multiple protocols supported for the config (env, file, http). For our use case, I don't think we need to support all of these, I'd be happy with just validating file paths and the file protocol for now (--config=./hybrid-agent-config.yml and file:hybrid-agent-config.yml).

If we expect the agent collector to support loading agent config from different protocols like otel does, then we should probably have a follow up ticket for it.

[kaanyalti]

@mauri870 looking at the otel collector code, I don't think we can enforce our clients to only use local files. The config provider interface allows users to provide config in any supported format

// Provider is an interface that helps to retrieve a config map and watch for any
// changes to the config map. Implementations may load the config from a file,
// a database or any other source.
//
// The typical usage is the following:
//
//	r, err := provider.Retrieve("file:/path/to/config")
//	// Use r.Map; wait for watcher to be called.
//	r.Close()
//	r, err = provider.Retrieve("file:/path/to/config")
//	// Use r.Map; wait for watcher to be called.
//	r.Close()
//	// repeat retrieve/wait/close cycle until it is time to shut down the Collector process.
//	// ...
//	provider.Shutdown()
type Provider interface {
	// Retrieve goes to the configuration source and retrieves the selected data which
	// contains the value to be injected in the configuration and the corresponding watcher that
	// will be used to monitor for updates of the retrieved value.
	//
	// `uri` must follow the "<scheme>:<opaque_data>" format. This format is compatible
	// with the URI definition (see https://datatracker.ietf.org/doc/html/rfc3986). The "<scheme>"
	// must be always included in the `uri`. The "<scheme>" supported by any provider:
	//   - MUST consist of a sequence of characters beginning with a letter and followed by any
	//     combination of letters, digits, plus ("+"), period ("."), or hyphen ("-").
	//     See https://datatracker.ietf.org/doc/html/rfc3986#section-3.1.
	//   - MUST be at least 2 characters long to avoid conflicting with a driver-letter identifier as specified
	//     in https://tools.ietf.org/id/draft-kerwin-file-scheme-07.html#syntax.
	//   - For testing, all implementation MUST check that confmaptest.ValidateProviderScheme returns no error.
	//
	// `watcher` callback is called when the config changes. watcher may be called from
	// a different go routine. After watcher is called Retrieved.Get should be called
	// to get the new config. See description of Retrieved for more details.
	// watcher may be nil, which indicates that the caller is not interested in
	// knowing about the changes.
	//
	// If ctx is cancelled should return immediately with an error.
	// Should never be called concurrently with itself or with Shutdown.
	Retrieve(ctx context.Context, uri string, watcher WatcherFunc) (*Retrieved, error)

	// Scheme returns the location scheme used by Retrieve.
	Scheme() string

	// Shutdown signals that the configuration for which this Provider was used to
	// retrieve values is no longer in use and the Provider should close and release
	// any resources that it may have created.
	//
	// This method must be called when the Collector service ends, either in case of
	// success or error. Retrieve cannot be called after Shutdown.
	//
	// Should never be called concurrently with itself or with Retrieve.
	// If ctx is cancelled should return immediately with an error.
	Shutdown(ctx context.Context) error
}

I may be missing some config option that may make implementation of this issue simpler. I have a meeting with @michalpristas tomorrow to discuss the implementation details here. Hopefully we can figure something out.

[kaanyalti]

Looking at the otel cli flags we have, I think we are relaying whatever config path is provided directly to otel, so we are not putting any restrictions here either. I am guessing this is the intended behaviour as we want the otel collector to behave the same as it does outside of the agent

func getConfigFiles(cmd *cobra.Command, useDefault bool) ([]string, error) {
	configFiles, err := cmd.Flags().GetStringArray(otelConfigFlagName)
	if err != nil {
		return nil, fmt.Errorf("failed to retrieve config flags: %w", err)
	}

[kaanyalti]

After discussing with @michalpristas, here's what I will implement

• Use otel resolver to et all the config
• Strip away non-otel components from the config files
• Save the configs to a new dir
• Pass this new dir and the config files into the otel command

[kaanyalti]

ok, another quick update. I spoke too soon, what I mentioned above seems to be not possible without reimplementing what otel has as the functions that may make this implementation possible are not exported. I am going to prepare a document explaining why this implementation is not possible at the moment, and will possibly propose a change in otel.

[kaanyalti]

Ok found a way to implement this, will post a PR as soon as I have a draft that demonstrates what I'm doing