modifying-builtin-plugins

Modifying Built-in Plugins

Built-in plugins are WASM components that ship with Golem and are automatically provisioned at registry service startup. Currently the only built-in plugin is the OTLP exporter oplog processor.

Plugin Location

plugins/
  otlp-exporter/                    # Golem application project (standalone workspace)
    components-rust/otlp-exporter/
      src/lib.rs                    # Plugin entry point
      src/config.rs                 # Configuration parsing
      src/export.rs                 # OTLP HTTP export logic
      src/processing.rs            # Oplog entry processing
      src/state.rs                 # Worker state management
      src/otlp_json.rs             # OTLP JSON types
      src/helpers.rs               # Utility functions
      golem.yaml                   # Component manifest (includes copy command)
    Cargo.toml                      # Workspace Cargo.toml (NOT part of main workspace)
    golem.yaml                      # Application manifest
  otlp-exporter.wasm                # Compiled WASM — COMMITTED TO GIT

Important: The plugins/otlp-exporter/ directory is a standalone Golem application with its own workspace. It is NOT part of the main Golem Cargo workspace. It depends on the Rust SDK at sdks/rust/golem-rust via a relative path.

Building Plugins

Important: Plugin builds require the golem CLI binary built from the current source tree. Always build it first and use the binary from target/debug/.

Step 1: Build the golem CLI

cargo make build

This compiles the golem binary to target/debug/golem.

Step 2: Build the plugin using the local golem binary

Using cargo-make (preferred for CI / full builds)

cargo make build-plugins

This runs:

1. target/debug/golem build -P release --force-build in plugins/otlp-exporter/
2. target/debug/golem exec -P release copy to copy the output WASM to plugins/otlp-exporter.wasm

Manual build (for iterating on plugin code)

Use the locally built binary (GOLEM below refers to the absolute path to target/debug/golem):

cd plugins/otlp-exporter
../../target/debug/golem build -P release --force-build
../../target/debug/golem exec -P release copy

The copy custom command (defined in components-rust/otlp-exporter/golem.yaml) copies the release WASM from golem-temp/agents/otlp_exporter_release.wasm to plugins/otlp-exporter.wasm.

After rebuilding

The compiled plugins/otlp-exporter.wasm must be committed to git. It is consumed at compile time by the golem CLI binary via include_bytes! and at runtime by the test framework.

How Plugins Are Loaded

In the golem CLI (local mode)

The WASM is embedded at compile time:

// cli/golem/src/launch.rs
static OTLP_EXPORTER_WASM: &[u8] = include_bytes!("../../../plugins/otlp-exporter.wasm");

In the test framework

The WASM is loaded from the filesystem at runtime:

// golem-test-framework/src/components/registry_service/spawned.rs
let otlp_wasm = working_directory.join("../plugins/otlp-exporter.wasm");

The path is passed to the registry service via the GOLEM__BUILTIN_PLUGINS__OTLP_EXPORTER_WASM_PATH environment variable.

In the registry service

The bootstrap code in golem-registry-service/src/bootstrap/mod.rs loads the WASM from the configured path, then calls provision_builtin_plugins() which:

1. Creates or finds the golem-system application
2. Creates or finds the builtin-plugins environment
3. Uploads the WASM as the otlp-exporter component
4. Deploys the builtin-plugins environment
5. Registers the golem-otlp-exporter plugin (version defined in builtin_plugin_provisioner.rs)
6. Grants the plugin to all existing environments

Configuration

The BuiltinPluginsConfig struct in golem-registry-service/src/config.rs:

pub struct BuiltinPluginsConfig {
    pub enabled: bool,
    pub otlp_exporter_wasm: Option<Arc<[u8]>>,       // Set programmatically
    pub otlp_exporter_wasm_path: Option<PathBuf>,     // From config/env var
}

Environment variables:

• GOLEM__BUILTIN_PLUGINS__ENABLED — enable/disable plugin provisioning
• GOLEM__BUILTIN_PLUGINS__OTLP_EXPORTER_WASM_PATH — filesystem path to the WASM file

Plugin Versioning

The plugin name and version are constants in golem-registry-service/src/services/builtin_plugin_provisioner.rs:

const OTLP_PLUGIN_NAME: &str = "golem-otlp-exporter";
const OTLP_PLUGIN_VERSION: &str = "1.5.0";

When updating the plugin, bump OTLP_PLUGIN_VERSION if the plugin spec changes.

Common Workflows

Modifying plugin logic

1. Edit source files in plugins/otlp-exporter/components-rust/otlp-exporter/src/
2. Build the golem CLI first: cargo make build
3. Build the plugin: cd plugins/otlp-exporter && ../../target/debug/golem build -P release --force-build && ../../target/debug/golem exec -P release copy
4. Verify plugins/otlp-exporter.wasm was updated
5. Commit the updated WASM file
6. Rebuild the main project (cargo make build) if testing with the embedded CLI

Changing the plugin SDK dependency

The plugin uses golem-rust from sdks/rust/golem-rust with the export_oplog_processor feature. If the SDK changes:

1. Rebuild the SDK if needed (see sdk-development skill)
2. Build the golem CLI: cargo make build
3. Rebuild the plugin: cd plugins/otlp-exporter && ../../target/debug/golem build -P release --force-build && ../../target/debug/golem exec -P release copy
4. Commit the updated WASM

Modifying provisioning logic

The provisioning code is in golem-registry-service/src/services/builtin_plugin_provisioner.rs. Changes there only require rebuilding golem-registry-service, not the plugin WASM.

Testing

The OTLP plugin integration test is at integration-tests/tests/otlp_plugin.rs. Run it with:

cargo test -p integration-tests -- otlp_plugin --report-time