> ## Documentation Index
> Fetch the complete documentation index at: https://docs.odigos.io/llms.txt
> Use this file to discover all available pages before exploring further.

# Custom Instrumentation

> The "Custom Instrumentation" rule can be used to instrument specific functions in Go, Java, or PHP applications.

## Considerations

If you wish to create custom instrumentations for Go, Java, or PHP applications, you can define a "Custom Instrumentation" rule via the Odigos InstrumentationRule CRD or the Odigos UI.

This feature is a great way to extend Odigos's auto-instrumentation capabilities to cover your specific use cases and application logic.

For Go and Java, custom instrumentation is applied dynamically via eBPF. For PHP, probes are delivered as environment variables and require a pod restart to take effect.

## Configuration Options

<AccordionGroup>
  <Accordion title="Golang">
    <Warning>
      When `functionName` is specified, `receiverName` and `receiverMethodName` must NOT be specified, and vice versa, if `receiverName` and `receiverMethodName` are specified, `functionName` must NOT be specified.

      `packageName` is required in all cases.
    </Warning>

    <AccordionGroup>
      <Accordion title="packageName">
        **packageName** `string` - The name of the package containing the function to instrument.

        * This field is *required*
      </Accordion>

      <Accordion title="functionName">
        **functionName** `string` - The name of the function to instrument.

        * This field is *optional*
      </Accordion>

      <Accordion title="receiverName">
        **receiverName** `string` - The name of the receiver type if the function is a method.

        * This field is *optional*
      </Accordion>

      <Accordion title="receiverMethodName">
        **receiverMethodName** `string` - The name of the method receiver if the function is a method.

        * This field is *optional*
      </Accordion>
    </AccordionGroup>
  </Accordion>

  <Accordion title="Java">
    <AccordionGroup>
      <Accordion title="className">
        **className** `string` - The fully qualified name of the class containing the method to instrument.

        * This field is *required*
      </Accordion>

      <Accordion title="methodName">
        **methodName** `string` - The name of the method to instrument.

        * This field is *required*
      </Accordion>
    </AccordionGroup>
  </Accordion>

  <Accordion title="PHP">
    <AccordionGroup>
      <Accordion title="className">
        **className** `string` - The fully qualified class name to instrument. Leave empty for a global function.

        * This field is *optional*
      </Accordion>

      <Accordion title="functionName">
        **functionName** `string` - The name of the function or method to instrument.

        * This field is *required*
      </Accordion>
    </AccordionGroup>
  </Accordion>
</AccordionGroup>

## Basic Example

The following example shows how to create a "Custom Instrumentation" rule that instruments a function named `ProcessOrder` in the `github.com/example/ecommerce` package.

<Steps>
  <Step>
    Create a YAML file named `custom-instrumentation.yaml` with the following content:

    <Accordion title="Package and function (Golang)">
      ```yaml theme={null}
      apiVersion: odigos.io/v1alpha1
      kind: InstrumentationRule
      metadata:
          name: custom-instrumentation-rule
          namespace: odigos-system
      spec:
          ruleName: "Custom Instrumentation for ProcessOrder"
          customInstrumentations:
              golang:
                - packageName: "github.com/example/ecommerce"
                  functionName: "ProcessOrder"
      ```
    </Accordion>

    <Accordion title="Receiver method (Golang)">
      ```yaml theme={null}
      apiVersion: odigos.io/v1alpha1
      kind: InstrumentationRule
      metadata:
          name: custom-instrumentation-rule
          namespace: odigos-system
      spec:
          ruleName: "Custom Instrumentation for ProcessOrder Method"
          customInstrumentations:
              golang:
                - packageName: "github.com/example/ecommerce"
                  receiverName: "OrderProcessor"
                  receiverMethodName: "ProcessOrder"
      ```
    </Accordion>

    <Accordion title="Class and method (Java)">
      ```yaml theme={null}
      apiVersion: odigos.io/v1alpha1
      kind: InstrumentationRule
      metadata:
          name: custom-instrumentation-rule
          namespace: odigos-system
      spec:
          ruleName: "Custom Instrumentation for getCurrencyInfo"
          customInstrumentations:
              java:
                - className: "com.example.CurrencyService"
                  methodName: "getCurrencyInfo"
      ```
    </Accordion>

    <Accordion title="Class and function (PHP)">
      ```yaml theme={null}
      apiVersion: odigos.io/v1alpha1
      kind: InstrumentationRule
      metadata:
          name: custom-instrumentation-rule
          namespace: odigos-system
      spec:
          ruleName: "Custom Instrumentation for processOrder"
          customInstrumentations:
              php:
                - className: "App\\Service\\OrderService"
                  functionName: "processOrder"
      ```
    </Accordion>
  </Step>

  <Step>
    Apply the action to the cluster:

    ```shell theme={null}
    kubectl apply -f custom-instrumentation.yaml
    ```
  </Step>
</Steps>