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xk6-output-timestream

Output k6 results to AWS Timestream so that you can run a performant, low-cost load test.

Why?

If you're here you've probably chosen to use k6 already and you're probably interested in using an AWS serverless service. These give you the benefits of:

For more information see the alternatives.

Using this extension lets you hook up K6 to AWS Timestream - plus you get a nice looking Grafana dashboard 😉 based off the K6 Load Testing Results dashboard.

Example Grafana dashboard

Usage

This output is written as an extension to K6 using xk6 extensions.

You can use this extension by either:

Configuration

Include the argument --out timestream when using the k6 run command - see the K6 docs

For all configuration specific to this extension see the Config struct in config.go.

The key bits of config you'll need to setup are the following environment variables

K6_TIMESTREAM_DATABASE_NAME
K6_TIMESTREAM_TABLE_NAME

You'll also need to setup your AWS credentials - see the guide on how to do this.

Tags Usage and Requirement

The timestream record dimensions (see timestream concepts) for each metric emmitted by k6 are taken from any k6 tags that have non-empty values.

Every timestream record requires at least one dimension when written, and k6 applies some default tags to metrics emmitted by many core k6 JavaScript API objects such as http requests, groups and checks. However, since some metrics emitted in the global/test scope may not have any k6 default tags, you will likely see the error At least one dimension is required for a record. logged from timestream if you do not define at least one custom tag at the topmost scope of your script to cover metrics with no default tags, as in an options object export. More information can be found in the K6 documentation or an example of setting up tags can be found in the integration test script.

Grafana Dashboard

An example dashboard is provided. You can use this dashboard by running make grafana-build grafana-run. If you are using this with your own test scripts, ensure that you include the instance_id and vu tags in your test script - see the integration test script as an example.

Troubleshooting

Building with other extensions

Between versions of K6 there can be breaking changes for extensions. So, if you're seeing issues using this extension with another extension then first ensure that the two extensions are using the same version of the K6 module. You can usually find the version of the K6 module in the go.mod in the extension's repo - the version will be next to the text go.k6.io/k6.

You may need to switch to an older version of this (or other) extensions to find a common k6 version. To find out the versions of this extension that correspond to particular K6 versions you can use the commit history. To do this, clone the repo (e.g. git clone https://github.com/leonyork/xk6-output-timestream.git) and run git log --grep=go.k6.io/k6. This will give you something that looks like:

commit 0516c682077778489b9f50c22c7d617eb6f69dd5 (HEAD -> docs/faq, tag: v0.9.62, origin/main, origin/HEAD, main)
Author: renovate[bot] <29139614+renovate[bot]@users.noreply.github.com>
Date:   Mon Nov 11 18:36:44 2024 +0000

    fix(deps): update module go.k6.io/k6 to v0.55.0

commit 2a769222eb717e028f2c4b01beec20b54d3c6ead (tag: v0.9.53)
Author: renovate[bot] <29139614+renovate[bot]@users.noreply.github.com>
Date:   Mon Sep 30 16:20:32 2024 +0000

    fix(deps): update module go.k6.io/k6 to v0.54.0

Here you can see which commit, and which version (see tag) of this extension, included a particular version of the K6 module. For example, if you needed to use k6 module v0.54.0, then you could choose v0.9.53 of this extension.

However, you'd be better off using version just before the k6 module was upgraded so that you have as many updates and fixes included as possible. If you'd like to do this, you'll want to use the version of this extension that's one below the commit that upgraded away from the version you need. For example, if you needed to use k6 module v0.54.0 again, but you wanted to use the latest version of this extension supporting that version of the k6 module, then you can see the upgrade away from v0.54.0 (to v0.55.0) happens in v0.9.62, so taking one version back, you'd want to use v0.9.61 of this extension.

For more information on the versioning system this extension uses, see semantic versioning.

If you find that this extension isn't using the latest version of the K6 module, you can submit a PR (although version updates are handled fully automatically by renovate). Without a very strong reason - such as a security vulnerability - PRs won't be accepted to roll back to a previous version of the K6 module.

Development

I use VSCode for development so this will be the best supported editor. However, you should be able to use other IDEs. If you are using another IDE:

  1. The devcontainer Dockerfile ci target shows all the tools you need for a dev environment (e.g. For linting).
  2. There are suggested tools you can also use.

VSCode

The preferred way to develop using VSCode is to use the dev container feature. This will mean you have all the tools required and suggested for development.

If you do want to use different tools (e.g. you don't like the shell setup), create .devcontainer/tools.override.sh and base it off .devcontainer/tools.default.sh.

If you don't want to use dev containers, you'll need to make sure you install the tools from the devcontainer Dockerfile and the packages in suggested tools that are needed for the VSCode extensions.

Where to start for development

output.go contains the logic for converting from K6 metric samples to AWS Timestream records and then saving those records.

There are targets for different development tasks in the Makefile.

Architecture

Metric samples are passed from each of the K6 VUs to metricSamplesHandler. This converts them to the format that the Timestream SDK expects and holds on to them until it has 100 records to save (the max batch size for Timestream). It will then save these asyncronously by kicking off a new go-routine to perform the save.

The channel for receiving metric samples is closed at the end of the test and the left-over records are saved.

  graph TD;

    K6-VU1.AddMetricSamples--metric samples-->metricSamplesHandler
    K6-VU2.AddMetricSamples--metric samples-->metricSamplesHandler
    K6-VUN.AddMetricSamples--metric samples-->metricSamplesHandler

    metricSamplesHandler--have 100 samples?-->writeRecordsAsync
    metricSamplesHandler--shutting down?-->writeRecordsAsync

    writeRecordsAsync--new go routine-->writeRecords

Testing

Integration

The integration tests work by creating a Timestream database and table, running a load test (with a built in test script) and then checking the results.

  graph LR;
    Client--deploy-->Timestream;
    Client--build-->k6;
    Client--run-->k6;
    k6-->nginx-fake-api
    k6--write-->Timestream;
    Client--build-->Tests;
    Client--run-->Tests;
    Tests--query-->Timestream;
    Client--destroy-->Timestream;

To run the integration tests you'll need to setup AWS credentials - see the guide on how to do this.

To deploy the Timestream database run make deploy-infra.

To run the tests (build, run and query steps above) run make test-integration. Note that you will need to build the k6 image first with make build-image.

To destroy the Timestream database run make destroy-infra.

Grafana

Testing of the Grafana dashboard is manual:

  1. export K6_ITERATIONS=40000 - to get a reasonable number of results, set the number of iterations to a large number.
  2. make deploy-infra - to deploy the infrastructure.
  3. make test-integration - to run the tests. These will likely fail as the number of iterations is not what the tests expect.
  4. make grafana-build grafana-run and browse to http://localhost:3000. From the dashboard you'll see the results come in. It should look like the dashboard near the top.
  5. make destroy-infra - to destroy the infrastructure once you're done testing.