varnishotel: Export OpenTelemetry data from Varnish

varnishotel operates as a sidecar along a Varnish instance and exports OpenTelemetry telemetry data.

Its notable features encompass:

• Traces: Provides insights in request processing.
• Logs: Not implemented.
• Metrics: Not implemented.

Why OpenTelemetry?

OpenTelemetry emerges as the standard for exporting operational telemetry data and is a CNCF top-level project.

Why OpenTelemetry in Varnish?

Inspired by the blog post Tech Preview: varnish-otel by Varnish Software, this project aims to combine the power of varnishstat and varnishlog (or similar tools) with the standard of OpenTelemetry to serve as a single place of observability in Varnish deployments.

Challenges for Observability in Varnish

Varnish provides powerful monitoring tools like varnishstat and varnishlog out of the box. However, they are not capable of exposing the data to external monitoring systems and require wrappers around them such as:

• jonnenauha/prometheus_varnish_exporter for exposing varnishstat metrics to Prometheus
• varnish/varnishlog-json to convert Varnish internal logs to JSON. This approach requires an external collector like fluent-bit, Logstash or vector to execute the program and export the logs for long-term storage.