This document will help you learn about logging in NBomber tests, options to configure, and also it gives you an introduction to Serilog logger and data sinks.

Logging in NBomber tests


NBomber is using Serilog library for logging. You don't need to install it, it's included already.

In order to start logging you need to take Step.Context or Scenario.Context (depending on your execution phase) and access Logger interface. Here is an example:

let step = Step.create("step_name", fun context -> task {
context.Logger.Information("hello from step!")
return Response.Ok()
Scenario.create "scenario_name" [step]
|> Scenario.withInit(fun context -> task {
context.Logger.Information("test started!")
|> Scenario.withClean(fun context -> task {
context.Logger.Information("test stopped!")

If you want to use logger out of NBomber context you can get access via static property.

Log.Logger.Information("hello world!")

Configuring logging

By default NBomber logger writes logs only to console and file sinks with the following configuration.


What is sink?

Structured log events (messages) are written to sinks and each sink is responsible for writing it to its own backend, database, store etc.

  • Console sink is a mandatory sink which NBomber use to print out text on console. This sink can't be customized or overridden. Console sink prints only Info and Warning logs.
  • File sink is a mandatory sink which NBomber use to write logs into file. This sink can't be customized or overridden. Also, File sink writes all types of logs (Verbose, Debug, Info, Warning, Error, Fatal), therefore if you decide to trace some request/response payload this sink is way to go.
// by default NBomber sets MinimumLevel to Debug (you can override it)
// Console sink settings: writes to console only Info and Warning logs
.Filter.ByIncludingOnly(fun event ->
event.Level = LogEventLevel.Information
|| event.Level = LogEventLevel.Warning
// File sink settings: writes to file all types of logs
path = "./logs/nbomber-log-" + testInfo.SessionId + ".txt",
outputTemplate = "{Timestamp:yyyy-MM-dd HH:mm:ss.fff zzz} [{Level:u3}] [{ThreadId}] {Message:lj}{NewLine}{Exception}",
rollingInterval = RollingInterval.Day

You can enrich or customize default logger configuration using some other sinks.


Make sure that you always return a new instance (not from a variable) of LoggerConfiguration. This limitation is mandatory since Serilog logger does not allow to create multiple instances from the same instance of LoggerConfiguration.

// here we set MinimumLevel to Verbose (it could be useful for tracing)
NBomberRunner.withLoggerConfig(fun () ->

Another way that is more appropriate for production use cases is configuring logger via infrastructure config file.

/// Loads infrastructure configuration.
/// The following formats are supported:
/// - json (.json),
/// - yaml (.yml, .yaml).
NBomberRunner.loadInfraConfig "infra-config.json"

You can also use NBomber CLI to dynamically specify file path to the infrastructure config.

Here is an example of infrastructure config file.

"Serilog": {
"Using": ["Serilog.Sinks.File"],
"MinimumLevel": "Debug",
"WriteTo": [{
"Name": "File",
"Args": {
"path": "./logs/nbomber-log.txt",
"outputTemplate": "{Timestamp:yyyy-MM-dd HH:mm:ss.fff zzz} [{Level:u3}] {Message:lj}{NewLine}{Exception}",
"rollingInterval": "Day"

Elasticsearch integration

Serilog supports many data storages to save your logs. You can check this list. But the most used is Elasticsearch. Let's try to integrate our NBomber with Elasticsearch to ship our logs there and be able to analyze them using full-text search or aggregation queries.


Installation prerequisites

You should have installed Elasticsearch database. If you don't have you can use Docker setup.

Add Elasticsearch sink

dotnet add package Serilog.Sinks.Elasticsearch

Configure Elasticsearch sink

|> NBomberRunner.withLoggerConfig(fun () ->
.WriteTo.Elasticsearch(nodeUris = "http://localhost:9200",
indexFormat = "custom-index-{0:yyyy.MM}",
batchPostingLimit = 0)

For more information about Elasticsearch sink configuration, please use this link.