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Invocation Context

Invocation Context

Golem associates an invocation context with each worker invocation. This invocation context consists of a stack of spans, each having a collection of attributes. Currently only string attributes are supported.

The invocation context can be queried and manipulated (by adding custom spans with custom attributes) using Golem specific host functions.

By default the invocation context's spans are not used by Golem for anything - it is just information propagated among workers to be used by either the workers, or oplog processor plugins installed to them. It is possible to reconstruct all information about invocation context from the oplog, so oplog processor plugins can be used for example to provide live traces of workers through OpenTelemetry.

Automatic invocation context spans

Incoming HTTP requests

The root spans of an invocation are containing information depending on how that invocation was started. When invoking through the invocation REST API, W3C Trace Context (opens in a new tab) headers are automatically processed to set the root trace-id and parent span-id.

When using custom APIs, the same headers are also taken into account by default, but it is also possible to write a custom Rib script per endpoint to extract more information from the HTTP requests and define custom span attributes with them.

In both cases, when the invocation's trigger is a HTTP request, a spans is added with the following attributes:

  • request.method
  • request.uri
  • request.remote_addr

Invocations

When an invocation reaches a worker, a new span is created containing the following attributes:

  • name: span's name (invoke-exported-function)
  • idempotency_key: unique identifier of the invocation
  • function_name: the fully qualified function name
  • worker_id: worker's id (consists of component ID and worker name)

Outgoing HTTP requests

Outgoing HTTP requests are also represented by their own automatic spans with the following attributes:

  • name: span's name (outgoing-http-request)
  • request.method: the outgoing request's HTTP method
  • request.uri: the outgoing request's URI

RPC calls

RPC calls on the caller side are also represented by a custom spans. First a span is created when the underlying RPC resource is initialized, with the following attributes:

  • name: span's name (rpc-connection)
  • target_worker_id: the target worker's ID

Within this span, a new span is created for each remote invocation, with the following attributes:

  • name: span's name (rpc-invocation)
  • function_name: the invoked function's fully qualified name
  • idempotency_key: the unique identifier of the invocation
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