Context processor

The purpose of this code is quickly integrate a new component "Context processor" in OpenTelemetry collector. This is a temporary solution while this functionality is not available in upstream.

You can read about what Context Processor does in otelcol-dev/contextprocessor/README.md. And you can see an example configuration in otelcol-dev/otelcol.yaml

About

This is a quick hands-on guide, describing a basic and minimum setup of a custom metrics processor. There are no tests, information about styles, best practices ... You can see this repo as a short version of https://opentelemetry.io/docs/collector/custom-collector/

Also, to get starting contributing in OpenTelemetry, please have a look at these resources:

• OpenTelemetry Collector: https://github.com/open-telemetry/opentelemetry-collector/blob/main/CONTRIBUTING.md
• OpenTelemetry Collector-Contrib: https://github.com/open-telemetry/opentelemetry-collector-contrib/blob/main/CONTRIBUTING.md

Starting ...

1. Get golang installed: https://go.dev/doc/install
2. Install the ocb tool: https://github.com/open-telemetry/opentelemetry-collector/releases

... from zero

If you want to get to your own custom collector:

1. Generate a builder-config.yaml. Adjust name, output_path, otelcol_version and the gomod versions, if needed.

   cat <<EOF > builder-config.yaml
   dist:
       name: otelcol-dev
       description: Basic OTel Collector distribution for Developers
       output_path: ./otelcol-dev
       otelcol_version: 0.88.0
   
   extensions:
   - gomod: go.opentelemetry.io/collector/extension/zpagesextension v0.88.0
   - gomod: go.opentelemetry.io/collector/extension/ballastextension v0.88.0
   - gomod: github.com/open-telemetry/opentelemetry-collector-contrib/extension/pprofextension v0.88.0
   
   exporters:
   - gomod: go.opentelemetry.io/collector/exporter/debugexporter v0.88.0
   - gomod: go.opentelemetry.io/collector/exporter/otlpexporter v0.88.0
   - gomod: go.opentelemetry.io/collector/exporter/otlphttpexporter v0.88.0
   - gomod: github.com/open-telemetry/opentelemetry-collector-contrib/exporter/prometheusremotewriteexporter v0.88.0
   
   processors:
   - gomod: go.opentelemetry.io/collector/processor/batchprocessor v0.88.0
   - gomod: go.opentelemetry.io/collector/processor/memorylimiterprocessor v0.88.0
   - gomod: github.com/open-telemetry/opentelemetry-collector-contrib/processor/attributesprocessor v0.88.0
   - gomod: github.com/open-telemetry/opentelemetry-collector-contrib/processor/filterprocessor v0.88.0
   - gomod: github.com/open-telemetry/opentelemetry-collector-contrib/processor/groupbyattrsprocessor v0.88.0
   - gomod: github.com/open-telemetry/opentelemetry-collector-contrib/processor/resourceprocessor v0.88.0
   - gomod: github.com/open-telemetry/opentelemetry-collector-contrib/processor/routingprocessor v0.88.0
   - gomod: github.com/open-telemetry/opentelemetry-collector-contrib/processor/transformprocessor v0.88.0
   
   receivers:
   - gomod: go.opentelemetry.io/collector/receiver/otlpreceiver v0.88.0
   - gomod: github.com/open-telemetry/opentelemetry-collector-contrib/receiver/prometheusreceiver v0.88.0
   
   connectors:
   - gomod: go.opentelemetry.io/collector/connector/forwardconnector v0.88.0
   EOF
   

2. Run ocb --config builder-config.yaml. A new directory otelcol-dev (or what you have defined in output_path) is created. The code generated should not be touched, all changes should be done via the builder-config.yaml file. You can see the builder configuration of the OpenTelemetry contrib here: https://github.com/open-telemetry/opentelemetry-collector-contrib/blob/main/cmd/otelcontribcol/builder-config.yaml
3. Go to new otelcold-dev and you will see a new executable otelcol-dev (or the value defined in name). You can execute it by providing a basic configuration file otelcold-dev --config otelcol.yaml:

   cat <<EOF > otelcol.yaml
   extensions:
   health_check:
   pprof:
       endpoint: 0.0.0.0:1777
   zpages:
       endpoint: 0.0.0.0:55679
   
   receivers:
   prometheus:
       config:
       scrape_configs:
           - job_name: 'otel-collector'
           scrape_interval: 30s
           static_configs:
               - targets: ['0.0.0.0:8888']
   
   exporters:
   debug:
       verbosity: detailed
   
   service:
   telemetry:
       logs:
       level: "debug"
   pipelines:
       metrics:
       receivers: [prometheus]
       processors: []
       exporters: [debug]
   extensions: 
   - health_check
   - pprof
   - zpages
   

   With this configuration the collector will scrape its own metrics.

... from the current repo

You can have a look to the folder otelcol-dev/helloworldmetricsprocessor and start modifying the code. Or

1. Create a new directory like helloworldmetricsprocessor.
2. Create a new golang module go mod init github.com/jriguera/otel-helloworldprocessor/otelcol-dev/helloworldmetricsprocessor (change according to your choice)
3. Create new golang files. Use same package with same name as the directory helloworldmetricsprocessor:
   1. config.go to define the component parameters and the function to validate them.
   2. factory.go to define the facture which create instances of the new component. Use the name NewFactory and the factory provided by the component package (eg processor.NewFactory)
   3. Other files to run the task (eg processor.go).
4. Add the component to the section of builder-config.yaml with the same reference you used in the go mod init .... Create another section to replace this module name with the local directory created in point 1.

   processors:
   - gomod: github.com/jriguera/otel-helloworldprocessor/otelcol-dev/helloworldmetricsprocessor v0.88.0
   
   replaces:
   - github.com/jriguera/otel-helloworldprocessor/otelcol-dev/helloworldmetricsprocessor => ./helloworldmetricsprocessor
   

5. Finally run ocb --config builder-config.yaml to generate the binary with the new component