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HTTP plugin

This document will help you learn about NBomber.HTTP plugin in more detail.


NBomber.Http provides a simple API to define HTTP steps, calculate response size, apply assertions.


Add HTTP package into your project.

dotnet add package NBomber.Http 

Create HTTP load test

open System
open System.Net.Http

open FSharp.Control.Tasks.NonAffine

open NBomber.Contracts
open NBomber.FSharp
open NBomber.Plugins.Network.Ping
open NBomber.Plugins.Http.FSharp

let main argv =

// it's optional Ping plugin that brings additional reporting data
let pingConfig = PingPluginConfig.CreateDefault ""
let pingPlugin = new PingPlugin(pingConfig)

let httpFactory = HttpClientFactory.create()

let step = Step.create("simple step", clientFactory = httpFactory, execute = fun context ->
Http.createRequest "GET" ""
|> Http.withHeader "Accept" "text/html"
|> Http.withBody(new StringContent("{ some JSON }"))
|> Http.withCheck(fun response -> task {
return if response.IsSuccessStatusCode then Response.ok()
|> Http.send context

Scenario.create "nbomber-web-site" [step]
|> Scenario.withLoadSimulations [InjectPerSec(rate = 100, during = seconds 30)]
|> NBomberRunner.registerScenario
|> NBomberRunner.withWorkerPlugins [pingPlugin]
|> ignore

0 // return an integer exit code


NBomber.Http provides HTTP API that can be used to create/send request and check response. It supports HTTP protocol specific concepts like HEADERS, BODY, VERSION.

HTTP Request

NBomber.Http provides a convenient way to define HTTP request and then send it.

let httpFactory = HttpClientFactory.create();

let step1 = Step.create("step 1", clientFactory = httpFactory, execute = fun context ->
Http.createRequest "GET" ""
|> Http.send context

let step2 = Step.create("step 2", clientFactory = httpFactory, execute = fun context -> task {
let step1Response = context.GetPreviousStepResponse<HttpResponseMessage>()
let headers = step1Response.Headers
let! body = step1Response.Content.ReadAsStringAsync()

return! Http.createRequest "GET" ""
|> Http.send context

HTTP Version

By default, NBomber.Http sets HTTP Version 1.1 but you can override this.

Http.withVersion "2.0"

HTTP Headers

By default, NBomber.Http sets no headers but you can override this.

Http.withHeader "Accept" "application/json"


// here we set string content
Http.withBody(new StringContent json)

// here we set binary data
Http.withBody(new ByteArrayContent bytes)

HTTP Check Response

By default, NBomber.Http is using this check for every response but you can override it.

Http.withCheck(fun response -> task {
if response.IsSuccessStatusCode then
return Response.ok(response, statusCode = int response.StatusCode)
return = int response.StatusCode)

HTTP ClientFactory

NBomber.Http provides HttpClientFactory abstraction that can be used to init a base HttpClient that will be used within your test.


NBomberHttpClientFactory creates only one instance of HttpClient and uses it for all steps. You can override it if you need it.

let httpFactory = HttpClientFactory.create();

let step1 = Step.create("step 1", clientFactory = httpFactory, execute = fun context ->
Http.createRequest "GET" ""
|> Http.send context

HTTP Client Timeout

By default, NBomber.Http uses HttpClient with default timeout for 100 seconds. A Domain Name System (DNS) query may take up to 15 seconds to return or time out. You can adjust and set a cutom timeout.


Also, pay attention that NBomber Step has a default timeout for 1 second.

let myHttpClient = new HttpClient()
myHttpClient.Timeout <- seconds 5
let httpFactory = HttpClientFactory.create("my_http_factory", myHttpClient)


There may be situations when you need to trace your requests and responses. The NBomber.Http has built-in functionality for tracing every request/response. In order to start tracing you need to set minimum logging level to Verbose.

NBomberRunner.withLoggerConfig(fun () ->

Also, you can enable tracing via the infrastructure config file.

"Serilog": {
"MinimumLevel": "Verbose"

JSON parsing

To work with the JSON format, you can use any library you prefer. Here is a list of popular libraries:

Here is an example with using Newtonsoft.Json, but you can use any other.

Http.createRequest "GET" url
|> Http.withCheck(fun response -> task {
let! jsonBody = response.Content.ReadAsStringAsync()

// parse JSON
let posts =
|> JsonConvert.DeserializeObject<PostResponse[]>
|> Option.ofObj

match posts with
| Some ps when ps.Length > 0 -> return Response.ok()
| -> return

Best practices

  • To test HTTP use LoadSimulation.InjectPerSec since usually web server is an open system. You can read more here.
  • For debugging or tracing you can use LoadSimulation.KeepConstant with copies = 1 since for this simulation NBomber will use a single thread which is easier to debug.
  • Use Ping plugin to get more info about networking.
  • Convert your integration tests to load tests