xk6-loki

A k6 extension for pushing logs to Loki.

Getting started

1. Install xk6

   go install go.k6.io/xk6/cmd/xk6@latest

2. Checkout grafana/xk6-loki

   git clone https://github.com/grafana/xk6-loki
   cd xk6-loki

3. Build the extension

   make k6

Javascript API

Module k6/x/loki

The k6/x/loki module contains the Loki extension to interact with the Loki API. To import the module add

import loki from 'k6/x/loki';

on top of your test file.

Class Config(url, [timeout, ratio, cardinality, labels])

The class Config holds configuration for the Loki client. The constructor takes the following arguments:

argument	type	description	default
url	string	The full URL to Loki in format [${scheme}://][${tenant}[:${token}]]@${host}[:${port}]	-
timeout	integer	Request timeout in milliseconds, e.g. 10000 for 10s	10000
ratio	float	The ratio between JSON and Protobuf encoded batch requests for pushing logs Must be a number between (including) 0 (100% JSON) and 1 (100% Protobuf) This is only relevant for write scenarios.	0.9
cardinality	object	The cardinality (unique values) for labels, where the object key is the name of the label and the value is the maximum amount of different values it may have.	null
labels	Labels	A Labels object that contains custom label definitions.	null

Example:

import loki from 'k6/x/loki';
let conf = loki.Config("localhost:3100");

Class Labels(labels)

The class Labels allows the definition of custom labels that can be used instead of the built-in labels. An instance of this class can be passed as fifth argument to the loki.Config constructor.

argument	type	description	default
labels	object	An object of type string (label name) to list of strings (possibel label values).	-

Example:

import loki from 'k6/x/loki';
let labels = loki.Labels({
  "format": ["json", "logfmt"], // must contain at least one of the supported log formats
  "cluster": ["prod-us-east-0", "prod-eu-west-1"],
  "namespace": ["dev", "staging", "prod"],
  "container": ["nginx", "app-1", "app-2", "app-3"]
});

Class Client(config)

The class Client is a Loki client that can read from and write to a Loki instance. The constructor takes the following arguments:

argument	type	description	default
config	object	An instance of Config which holds the configuration for the client.	-

Example:

import loki from 'k6/x/loki';
let conf = loki.Config("localhost:3100");
let client = loki.Client(conf);

Method client.push()

This function is a shortcut for client.pushParameterized(5, 800*1024, 1024*1024).

Method client.pushParameterized(streams, minSize, maxSize)

Execute a push request (POST /loki/api/v1/push).

The function pushParameterized generates batch of logs and pushes it to the Loki instance. A batch consists of one or more streams which hold multiple log lines. A stream is a set of log lines with a unique set of labels.

argument	type	description	default
streams	integer	The amount of streams the pushed batch should contain.	-
minSize	integer	Minimum size in bytes of the raw log lines of the batch.	-
maxSize	integer	Maximum size in bytes of the raw log lines of the batch.	-

minSize and maxSize define the boundaries for a random value of the actual batch size.

Method client.instantQuery(query, limit)

This function is a shortcut for client.instantQueryAt(query, limit, time.Now()) where time.Now() is the current nanosecond.

Method client.instantQueryAt(query, limit, instant)

Execute an instant query (GET /loki/api/v1/query).

argument	type	description	default
query	string	The LogQL query to perform.	-
limit	integer	Maxiumum number of entries to return.	-
instant	integer	Nanosecond at which to execute query.	-

Method client.rangeQuery(query, duration, limit)

This function is a shortcut for client.rangeQueryAt(query, duration, limit, time.Now()) where time.Now() is the current nanosecond.

Method client.rangeQueryAt(query, duration, limit, instant)

Execute a range query (GET /loki/api/v1/query_range).

argument	type	description	default
query	string	The LogQL query to perform.	-
duration	string	The time span of the range, e.g. 15m, 1h, or 7d.	-
limit	integer	Maxiumum number of entries to return.	-
instant	integer	Nanosecond at which to execute query.	-

duration defines the range for the query and uses the current timestamp as end and current timestamp - duration as start.

Method client.labelsQuery(duration)

This function is a shortcut for client.labelsQueryAt(duration, time.Now()) where time.Now() is the current nanosecond.

Method client.labelsQueryAt(duration, instant)

Execute a labels query (GET /loki/api/v1/labels).

argument	type	description	default
duration	string	The time span for which labels should be returned, e.g. 15m, 1h, or 7d.	-
instant	integer	Nanosecond at which to execute query.	-

duration defines the range for the query and uses the current timestamp as end and current timestamp - duration as start.

Method client.labelValuesQuery(label, duration)

This function is a shortcut for client.labelValuesQueryAt(label, duration, time.Now()) where time.Now() is the current nanosecond.

Method client.labelValuesQueryAt(label, duration, instant)

Execute a label values query (GET /loki/api/v1/label//values).

argument	type	description	default
label	string	The label name for which to query the values.	-
duration	string	The time span for which label values should be returned, e.g. 15m, 1h, or 7d.	-
instant	integer	Nanosecond at which to execute query.	-

duration defines the range for the query and uses the current timestamp as end and current timestamp - duration as start.

Method client.seriesQuery(matchers, duration)

This function is a shortcut for client.seriesQueryAt(matchers, duration, time.Now()) where time.Now() is the current nanosecond.

Method client.seriesQueryAt(matchers, duration, instant)

Execute a series query (GET /loki/api/v1/series).

argument	type	description	default
matchers	list	A list of label matchers used for the query.	-
duration	string	The time span for which the matching series should be returned, e.g. 15m, 1h, or 7d.	-
instant	integer	Nanosecond at which to execute query.	-

duration defines the range for the query and uses the current timestamp as end and current timestamp - duration as start.

Labels

xk6-loki uses the following built-in label names for generating streams:

name	values	notes
instance	fixed: 1 per k6 worker
format	fixed: apache_common, apache_combined, apache_error, rfc3164, rfc5424, json, logfmt	This label defines how the log lines of a stream are formatted.
os	fixed: darwin, linux, windows	-
namespace	variable	1
app	variable	1
pod	variable	1
language	variable	1
word	variable	1

The total amount of different streams is defined by the carthesian product of all label values. Keep in mind that high cardinality impacts the performance of the Loki instance.

Custom labels

Additionally, xk6-loki also supports custom labels that can be used instead of the built-in labels.

See examples/custom-labels.js for a full example with custom labels.

Metrics

The extension collects metrics that are printed in the end-of-test summary in addition to the built-in metrics.

Query metrics

These metrics are collected only for instant and range queries.

name	description
loki_bytes_processed_per_second	amount of bytes processed by Loki per second
loki_bytes_processed_total	total amount of bytes processed by Loki
loki_lines_processed_per_second	amount of lines processed by Loki per second
loki_lines_processed_total	total amount of lines processed by Loki

Write metrics

name	description
loki_client_uncompressed_bytes	the quantity of uncompressed log data pushed to Loki, in bytes
loki_client_lines	the number of log lines pushed to Loki

Example

import sleep from 'k6';
import loki from 'k6/x/loki';

/**
 * URL used for push and query requests
 * Path is automatically appended by the client
 * @constant {string}
 */
const BASE_URL = `http://localhost:3100`;

/**
 * Client timeout for read and write in milliseconds
 * @constant {number}
 */
const timeout = 5000;

/**
 * Ratio between Protobuf and JSON encoded payloads when pushing logs to Loki
 * @constant {number}
 */
const ratio = 0.5;

/**
 * Cardinality for labels
 * @constant {object}
 */
const cardinality = {
  "app": 5,
  "namespace": 5
};

/**
 * Execution options
 */
export const options = {
  vus: 10,
  iterations: 10,
};

/**
 * Create configuration object
 */
const conf = new loki.Config(BASE_URL, timeout, ratio, cardinality);

/**
 * Create Loki client
 */
const client = new loki.Client(conf);

export default () => {
  // Push a batch of 2 streams with a payload size between 500KB and 1MB
  let res = client.pushParameterized(2, 512 * 1024, 1024 * 1024);
  // A successful push request returns HTTP status 204
  check(res, { 'successful write': (res) => res.status == 204 });
  sleep(1);
}

./k6 run examples/simple.js

You can find more examples in the examples/ folder.

Footnotes

1. The amount of values can be defined in cardinality argument of the client configuration. ↩ ↩² ↩³ ↩⁴ ↩⁵