ChangeLog

Version 2.4.0 (2026-04-13)

varnish-otel is now compatible with Varnish Cache >= 9.0.1. Note that tracing will still require vmod-otel, which is a Varnish Enterprise feature, but tracing and logging will work without extra configuration on the Varnish side.

Two new resource attributes are now automatically populated:

• varnish.version: detected using varnishd -V at startup.
• service.instance.id: seethe new OTEL_VARNISH_INSTANCE_ID variable below.

New environment variables:

• OTEL_VARNISH_INSTANCE_ID controls how service.instance.id is set:
  • none: doesn’t set the attribute.
  • uuid: generate a UUIDv4.
  • hostname: reads the hostname.
  • auto (default): , use the hostname if not empty, otherwise, generate a UUIDv4.
• OTEL_VARNISH_LOG_RECORD_FILTER allows to pass -x/-X/-i/-I arguments to varnishlog-json. This notably permits filtering sensitive headrs that shouldn’t be logged.

Other changes:

• Only metrics with a counter (c) or gauge (g) flag are exported; bitfield metrics are now ignored.
• Errors from the logging subprocesses are now logged at Warn level instead of Debug.
• Metrics are now parsed as uint64, preventing overflows on large counters.

Version 2.1.0 (2025-11-25)

This version focuses on finer logging, introducing new environment variables that will impact the internal use of varnishlog-json and varnishncsa.

New variables:

• OTEL_VARNISH_LOG_RATE_LIMIT passes a -R argument to varnishlog-json/varnishncsa to rate-limit the logs read by varnish-otel.
• OTEL_VARNISH_LOG_TOOL can be set to ncsa to use varnishncsa instead of varnishlog-json. This will result in fewer attributes available for each logs, but the TraceID and SpanID will be preserved if present.
• OTEL_VARNISH_NCSA_FORMAT_STRING passes a -f argument to varnishncsa to specify the log format to use.
• OTEL_VARNISH_DURATION_BUCKETS and OTEL_VARNISH_SIZE_BUCKETS define bucke sizes for histograms.
• OTEL_VARNISH_LOG_QUERY allows to filter out logs before they are processed by varnish-otel.

Version 2.0.0 (2025-11-17)

• Major rewrite of the metric exporter. This drastically reduce the memory consumption, notably on long running instances.
• More robust unmarshalling of varnishstat output.
• Unknown metric names get sanitized replacing illegal characters with underscores.
• Metrics RLCOL.(<collection>).accounts are now renamed varnish.rlcol.accounts{collection.name=<collection>}.
• New environment variable OTEL_VARNISH_PPROF_LISTEN will enable go’s pprof for debugging.

New histograms:

• varnish.backend.duration.connection
• varnish.backend.duration.total
• varnish.backend.duration.ttfb
• varnish.backend.request.bytes
• varnish.backend.response.bytes
• varnish.client.duration.total
• varnish.client.duration.ttfb
• varnish.client.duration.waitlist
• varnish.client.request.bytes
• varnish.client.response.bytes

Version 1.2.0 (2025-08-19)

• Fix crash when parsing an invalid req.url

Version 1.1.0 (2025-07-31)

• VCL can opt out of tracing using std.log("otel-tracing: false") to disable tracing for a specific transaction all its dependents.
• environment variables OTEL_TRACES_OPT_IN_ATTRIBUTES now accepts true and false for consistency with the other variable. on/off are still valid but will be deprecated at a later date.

Multiple counter translations have been added or changed:

Version 1.0.0 (2025-06-30)

• Initial Release.