k6 v0.41.0 is here! :tada: It has relatively few user-facing changes, but includes massive internal improvements that pave the way for some awesome features for the near future. Unfortunately, this work also required us to make a few minor breaking changes.

Breaking changes

Changes in the url, iter and vu system metric tags

As we warned in the release notes for k6 v0.39.0 and v0.40.0, we've been fundamentally refactoring the metrics sub-systems of k6. We now have efficient support for time series, which required a few minor user-facing breaking changes:

• If URL grouping is used for HTTP requests (that is, if the http.url helper is used or the name metric tag is specified), then the url tag in the resulting http_req_* metric samples will also have the same value as the name tag. Previously, k6 did this only for the cloud output, but now it does this universally (#2703).
• The vu and iter system tags, which are disabled by default, have been transformed into high-cardinality metrics metadata instead. It means that they will no longer be usable in thresholds, and various outputs may emit them differently or ignore them completely (#2726).

Changes in the Go metrics APIs

While the user-facing changes from our metrics refactoring are few and relatively minor, and there are no changes to JavaScript APIs yet, we have extensively refactored our internal Go APIs (#2594, #2726, #2727). The metrics.Sample and metrics.TagSet types are now entirely different. We also have high-cardinality metadata attributes in each Sample and at the VU level (see the combined TagsAndMeta code and how it is used in the per-VU State object).

k6 convert is officially deprecated (#2714)

k6 convert has been a sub-command to convert a HAR file recording of HTTP traffic into a preliminary k6 script that makes roughly the same requests. It has been long neglected and softly deprecated in favor of the newer and more feature-rich har-to-k6 standalone converter.

We have now officially deprecated k6 convert. The command still works and will continue to do so for a few more k6 versions. However, it's not visible from k6 --help and will emit a warning when used. Please see the documentation for the standalone har-to-k6 converter and open an issue (or comment on an existing one) if you have any problems with it.

New Features, enhancements, and UX improvements

• #2679 added support for maxReceiveSize and maxSendSize parameters in the gRPC's Client.connect() method. Thanks, @ariasmn!
• #2605 introduced a new --exclude-env-vars CLI flag to k6 archive that causes it to not include the provided environment variables in the resulting archive bundle's metadata.json file.
• #2700 added support for loading gRPC protoset files. Thanks, @jklipp!

Bug fixes

• #2678 fixed the Docker image labels. Thanks, @knittl, for reporting the problem (#2677)!
• #2689 fixed the REST API's Content-Type response header. Thanks, @wingyplus!
• #2691 fixed the detailed k6 version information embedded in the k6 releases.
• #2693 fixed a bug that made the k6 event loop unusable when a Promise rejection was left unhandled.
• #2696 fixed a problem with HTTP redirects with empty Location headers (#2474) by updating the Go version we use to compile k6 to 1.19.x. Thanks, @agilob!
• #2705 fixed a panic in the k6/net/grpc module (#2661). Thanks, @c47gao and @robpickerill!
• #2738 fixed a panic when a Promise was rejected with an undefined reason.
• #2739 fixed hidden stack traces in certain types of errors originating from k6's Go code.

Maintenance and internal improvements

We had a few minor changes in this release:

• #2687 improved our logging tests. Thanks, @nsmith5!
• #2696 updated the used Go version to 1.19.x and the Alpine version in our Docker image to 3.16. Thanks, @agilob!
• #2707, #2708, #2709, #2710 updated most of the Go dependencies k6 has.
• #2716 refactored how custom JS tags are applied to metrics and cleaned up validation for invalid tag values.

We also have a couple of significant improvements that will help us develop exciting new features soon:

Metric time series (#2594)

Previous to #2594, k6 didn't have an efficient way to group metric samples with the same tags. It meant that a whole class of applications for processing and aggregating metrics were nearly impossible to do or, at best, very inefficient.

At the cost of some minor breaking changes, we now have a performant internal representation to group metric samples with the same tags at the time of the action that generated them, i.e. the time of metric measurement. With this, k6 can efficiently group samples for the same action (e.g. an HTTP request to a specific URL) over time and construct time series with them.

Internal support for high-cardinality metrics metadata (#2726, #2727)

As described in the previous section, the efficient grouping of metric samples into time series works well for relatively low-cardinality data. However, k6 needed some way to attach high-cardinality metadata as well. This is necessary for data that's unique or random, such as Trace and Span IDs in distributed tracing or user IDs in tests with huge data sets.

k6 v0.41.0 has added support for attaching high-cardinality metadata to metric samples, and the vu and iter system tags have been transformed into such metadata (see the breaking changes section above), but it is not yet accessible from user scripts. There is no JavaScript API to modify this metadata, only built-in k6 Go modules and xk6 Go extensions can make use of it, for now.