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Version: 1.0

Logs

In addition to host-level logging, wasmCloud supports log exports using the OpenTelemetry (OTEL) specification.

For more information on wasmCloud's implementation of OpenTelemetry, including advanced configuration options, see Observability with OpenTelemetry.

Configuration​

By default, wasmCloud hosts write info level logs to stderr in plaintext.

To enable all OTEL signals, including logs, use the WASMCLOUD_OBSERVABILITY_ENABLED environment variable:

bash
WASMCLOUD_OBSERVABILITY_ENABLED="true"

To enable only logs, use the WASMCLOUD_LOGS_ENABLED environment variable:

bash
WASMCLOUD_LOGS_ENABLED="true"

Enabling OTEL signals automatically structures logs for OTEL export. (In this case, local stderr logs remain plaintext.)

wasmCloud hosts export structured logs via HTTP/OpenTelemetry Protocol (otlp) on port 4318.

The endpoint for exports may be overwritten with the OTEL_EXPORTER_OTLP_ENDPOINT environment variable:

bash
OTEL_EXPORTER_OTLP_ENDPOINT=http://my-custom-host:4318

See the host config options for equivalent host configuration CLI flags.

Log levels​

The wasmCloud host supports the following log levels:

  • error
  • warn
  • info (default)
  • debug
  • trace

To override the log level, use the --log-level host config argument.

warning

Take care when enabling trace or debug level logs in a production environment. These log levels may contain sensitive information.

Structured logs​

In a production environment, it's more common to emit logs in a structured format and aggregate logs from all hosts in a centralized location. Enabling OTEL signals automatically structures JSON logs for OTEL export, while local stderr logs remain plaintext.

To enable structured log output without enabling OTEL signals, use the --enable-structured-logging host config argument. This will cause the host to emit logs as JSON, which are suitable for forwarding to a log aggregator.

json
{
  "timestamp": "2024-01-09T17:54:59.113161Z",
  "level": "INFO",
  "fields": {
    "message": "wasmCloud host started",
    "host_id": "NDBYMWNPI3GSXBNM6H4WG6JTVB7K42KQWPOPICMIBVUXQL36ISJZHK4D"
  },
  "target": "wasmcloud_host::wasmbus"
}

Viewing logs with Grafana and Loki​

A set of sample configurations and Docker Compose files are available to help launch a local observability environment. After following the instructions to launch a wasmCloud observability ecosystem, you can navigate to http://localhost:5050/explore, click the dropdown in the upper left, and select "Loki" to view logs.

Refer to the environment variables in the Docker Compose file for a complete example configuration. The example uses Grafana and Loki, but wasmCloud works with any OTEL-compatible backend.