Public probes log http request & response with headers, can lead to truncated logs

[peterschretlen]

Problem:
k6 scripted synthetics tests on public probes log responses and requests including headers. In cases where 1) a script makes many http requests and/or 2) have a lot of header information, the log size can grow quickly. Once the combined logs payload reaches 255KiB, any further logs are truncated. This logging cannot be configured in the synthetic monitor.

Context:
Public probes are configured to use the K6_HTTP_DEBUG option ( docs ), which logs requests & responses (without the body). This is intended to help provide out-of-the-box visibility and troubleshooting without having to manually add logs.

In a recent escalation (internal ref), a customer had k6 scripted synthetic that make ~200 http requests, with sizeable request & response headers. This 255KiB limit was hit and logs were truncated, so they could not get the full set of logs.

Workaround: Private probes don't do this by default, unless you explicitly set the K6_HTTP_DEBUG environment variable.

A potential solution might be a way to opt-out of the debug logging on public probes, for customers who don't want these logs and/or are interested in minimizing log volume & cost. The tradeoff here is additional complexity in the form of options & toggles that need to be documented, maintained, tested, etc.

[peterschretlen]

In the case of the escalation, the request and response log lines were each about 2300 characters long, mostly due to cookie and session headers being logged.