HTTP Protocol

Learn about connection, redirect, caching, resource infering and dns resolution

HTTP is the main protocol Gatling targets, so that’s where we place most of our effort.

Gatling HTTP allows you to load test web applications, web services or websites. It supports HTTP and HTTPS with almost every existing feature of common browsers such as caching, cookies, redirect, etc.

However, Gatling is not a browser: it won’t run Javascript, won’t apply CSS styles and trigger CSS background-images download, won’t react to UI events, etc. Gatling works at the HTTP protocol level.


Use the http object in order to create an HTTP protocol.

As every protocol in Gatling, the HTTP protocol can be configured for a scenario. This is done thanks to the following statements:

val httpProtocol = http.baseUrl("")

val scn = scenario("myScenario") // etc...


Core parameters

Base URL

As you may have seen in the previous example, you can set a base URL. This base URL will be prepended to all urls that does not start with http, e.g.:

val httpProtocol = http.baseUrl("")

val scn = scenario("My Scenario")
    http("My Request")
  ) // will make a request to ""
    http("My Other Request")
  ) // will make a request to ""


Load testing several servers with client based load balancing

If you want to load test several servers at the same time, to bypass a load-balancer for example, you can use methods named baseUrls which accepts a String* or a List[String]:

val httpProtocol = http.baseUrls("", "", "")

Each virtual user will pick one of the baseUrl from the list once and for all when it starts, based on a round-robin strategy.

Automatic warm up

The Java/NIO engine start up introduces an overhead on the first request to be executed. In order to compensate this effect, Gatling automatically performs a request to

To disable this feature, just add .disableWarmUp to an HTTP Protocol Configuration definition. To change the warm up url, just add .warmUp("newUrl").

// override warm up URL to
val httpProtocol = http.warmUp("")
// disable warm up
val httpProtocolNoWarmUp = http.disableWarmUp

Engine parameters

Max connection per host

In order to mimic real web browser, Gatling can run multiple concurrent connections per virtual user when fetching resources on the same hosts. By default, Gatling caps the number of concurrent connections per remote host per virtual user to 6, but you can change this number with maxConnectionsPerHost(max: Int).

Gatling ships a bunch of built-ins for well-known browsers:

  • maxConnectionsPerHostLikeFirefoxOld
  • maxConnectionsPerHostLikeFirefox
  • maxConnectionsPerHostLikeOperaOld
  • maxConnectionsPerHostLikeOpera
  • maxConnectionsPerHostLikeSafariOld
  • maxConnectionsPerHostLikeSafari
  • maxConnectionsPerHostLikeIE7
  • maxConnectionsPerHostLikeIE8
  • maxConnectionsPerHostLikeIE10
  • maxConnectionsPerHostLikeChrome
// 10 connections per host.
val httpProtocolMax10Connections = http.maxConnectionsPerHost(10)
// Firefox max connections per host preset.
val httpProtocolMaxConnectionsLikeFirefox = http.maxConnectionsPerHostLikeFirefox

Connection Sharing

The default behavior is that every virtual user has its own connection pool and its own SSLContext. This behavior meets your needs when you want to simulate internet traffic where each virtual user simulates a web browser.

Instead, if you want to simulate server to server traffic where the actual client has a long-lived connection pool, you want to have the virtual users share a single global connection pool. You can achieve this behavior with the .shareConnections param.

HTTP/2 Support

HTTP/2 experimental support can be enabled with the .enableHttp2 option.

Note that you’ll either need your injectors to run with Java 9+, or make sure that gatling.http.ahc.useOpenSsl wasn’t turned to false in Gatling configuration.

val httpProtocol = http.enableHttp2

When HTTP/2 is enabled, Gatling will try to connect to your remotes using HTTP/2 through the ALPN protocol. If your remote supports HTTP/2, Gatling will use the protocol, and fall back to HTTP/1 otherwise. There is no specific code to add in the middle of your requests.

Next time you use that remote with the same user, if Gatling knows that your remote doesn’t support HTTP/2, it won’t try again and therefore won’t use ALPN.

One of the main purpose of HTTP/2 is to support multiplexing. This means that on a single connection, you are able to send multiple requests, without waiting for the responses, and receive these responses in whatever order. It means that, using HTTP/2, browsers and Gatling won’t open additional connections to the same remote for a given virtual user (assuming you don’t enable shareConnections) once they know that the remote is using HTTP/2. The first time Gatling encounters a remote, the connections will be opened like in HTTP/1 mode if there are multiple requests (for example in a resources statement). If the remote is using HTTP/1, these connections will be used if needed. If it is using HTTP/2, a single connection will be maintained, and the other ones will reach idle timeout and be closed.

It is possible to populate the Gatling cache concerning protocol and remotes before the run, using the http2PriorKnowledgeMap(Map[String, Boolean]) method on the protocol.

val httpProtocol = http.enableHttp2
  .http2PriorKnowledge(Map("" -> true, "" -> false))

With this method, you are able to tell Gatling that remotes support HTTP/2 or not. It means that if you are setting a remote to true (it supports HTTP/2), additional connections won’t be created the first time the remote is encountered in the simulation. If you are setting a remote to false (it doesn’t support HTTP/2), ALPN won’t be used, and additional connections will be created.

This option is useful to simulate users that already went to your website, and whose browsers already cached the fact that your website is using HTTP/2 or HTTP/1.

DNS Name Resolution

By default, Gatling uses Java’s DNS name resolution. This cache has a TTL of 30s by default on OpenJDK and doesn’t honor the DNS records’ own TTL. You can control the TTL with where N is a number of seconds. Please note the [ System property is deprecated and one should use the networkaddress.cache.ttl Security property instead, see doc.

If you’re using the Java DNS name resolution and have multiple IP (multiple DNS records) for a given hostname, Gatling will automatically shuffle them to emulate DNS round-robin.

You can use a Netty based DNS resolution instead, with .asyncNameResolution(). This method can take a sequence of DNS server adresses, eg .asyncNameResolution(""). If you don’t pass DNS servers, Gatling will use the ones from your OS configuration on Linux and MacOS only, and to Google’s ones on Windows(don’t run with heavy load as Google will block you).

You can also make it so that every virtual user performs its own DNS name resolution with .perUserNameResolution. This parameter is only effective when using asyncNameResolution.

Hostname Aliasing

You can of course define hostname aliases at the OS level in the /etc/hosts file.

But you can use .hostNameAliases to pass aliases programmatically:

val httpProtocol = http
  .hostNameAliases(Map("" -> List("", "")))

Virtual Host

One can set a different Host than the url one:

virtualHost(virtualHost: Expression[String])

Local address

You can bind the sockets from specific local addresses instead of the default one:

localAddress(localAddress: String)
localAddresses(localAddress1: String, localAddress2: String)
useAllLocalAddresses // automatically discover all bindable local addresses
useAllLocalAddressesMatching(regex1, regex2) // automatically discover all bindable local addresses matching one of the pattern parameters (String)

When setting multiple addresses, each virtual user is assigned to one single local address once and for all.


By default, Gatling uses the KeyManagerFactory configuration defined in gatling.conf, or if undefined, falls back to the JVM’s default one.

Then, it’s possible to have per virtual user KeyManagerFactories, typically if you want them to use different sets of keys:

perUserKeyManagerFactory(f: Long => KeyManagerFactory)

This function’s input is the virtual user’s id (if you need it to generate some file name) and returns a

Request building parameters

Automatic Referer

The Referer HTTP header can be automatically computed. This feature is enabled by default.

To disable this feature, just add .disableAutoReferer to an HTTP Protocol Configuration definition.


Gatling caches responses using:

  • Expires header
  • Cache-Control header
  • Last-Modified header
  • ETag

To disable this feature, just add .disableCaching to an HTTP Protocol Configuration definition.

Url Encoding

Url components are supposed to be urlencoded. Gatling will encode them for you, there might be some corner cases where already encoded components might be encoded twice.

If you know that your urls are already properly encoded, you can disable this feature with .disableUrlEncoding. Note that this feature can also be disabled per request.


Request stats are logged and then used to produce reports. Sometimes, some requests may be important for you for generating load, but you don’t actually want to report them. Typically, reporting all static resources might generate a lot of noise, and yet failed static resources might not be blocking from a user experience perspective.

Gatling provides several means to turn requests silent. Silent requests won’t be reported and won’t influence error triggers such as tryMax and exitHereIfFailed. Yet, response times will be accounted for in group times.

Some parameters are available here at protocol level, some others are available at request level.

Rules are:

  • explicitly turning a given request silent or notSilent has precedence over everything else
  • otherwise, a request is silent if it matches protocol’s silentUri filter
  • otherwise, a request is silent if it’s a resource (not a top level request) and protocol’s silentResources flag has been turned on
  • otherwise, a request is not silent

silentUri lets you pass a regular expression that would disable logging for ALL matching requests:


silentResources silences all resource requests, except the ones that were explicitly turned notSilent.

HTTP Headers

Gatling lets you set some generic headers at the http protocol definition level with:

  • header(name: String, value: Expression[String]): set a single header.
  • headers(headers: Map[String, String]): set a bunch of headers.


  .header("foo", "bar")
  .headers(Map("foo" -> "bar", "baz" -> "qix"))

You have also the following built-ins for the more commons headers:

  • acceptHeader(value: Expression[String]): set Accept header.
  • acceptCharsetHeader(value: Expression[String]): set Accept-Charset header.
  • acceptEncodingHeader(value: Expression[String]): set Accept-Encoding header.
  • acceptLanguageHeader(value: Expression[String]): set Accept-Language header.
  • authorizationHeader(value: Expression[String]): set Authorization header.
  • connectionHeader(value: Expression[String]): set Connection header.
  • contentTypeHeader(value: Expression[String]): set Content-Type header.
  • doNotTrackHeader(value: Expression[String]): set DNT header.
  • originHeader(value: Expression[String]): set Origin header.
  • userAgentHeader(value: Expression[String]): set User-Agent header.

Signature Calculator

You can set a function to sign a request once Gatling has built it, just before it’s being sent over the wire:

sign(calculator: Expression[SignatureCalculator])

We also provide a built-in for OAuth1:

signWithOAuth1(consumerKey: Expression[String], clientSharedSecret: Expression[String], token: Expression[String], tokenSecret: Expression[String])


You can set the authentication methods at protocol level with these methods:

  • basicAuth(username: Expression[String], password: Expression[String])
  • digestAuth(username: Expression[String], password: Expression[String])

Response handling parameters

Follow redirects

By default Gatling automatically follow redirects in case of 301, 302, 303, 307 or 308 response status code, you can disable this behavior with .disableFollowRedirect.

To avoid infinite redirection loops, Gatling sets a limit on the number of redirects. The default value is 20. You can tune this limit with: .maxRedirects(max: Int)

By default, Gatling will change the method to “GET” on 302 to conform to most user agents’ behavior. You can disable this behavior with .strict302Handling.

Response Transformers

Some people might want to process manually the response. Gatling protocol provides a hook for that need: transformResponse(responseTransformer: ResponseTransformer)


You can define checks at the http protocol definition level with: check(checks: HttpCheck*). They will be apply on all the requests, however you can disable them for given request thanks to the ignoreProtocolChecks method.

Resource inferring

Gatling can fetch resources in parallel in order to emulate the behavior of a real web browser.

At the protocol level, you can use inferHtmlResources methods, so Gatling will automatically parse HTML to find embedded resources and load them asynchronously.

The supported resources are:

  • <script>
  • <base>
  • <link>
  • <bgsound>
  • <frame>
  • <iframe>
  • <img>
  • <input>
  • <body>
  • <applet>
  • <embed>
  • <object>
  • import directives in HTML and @import CSS rule.

Other resources are not supported: css images, javascript triggered resources, conditional comments, etc.

You can also specify black/white list or custom filters to have a more fine grain control on resource fetching. WhiteList and BlackList take a sequence of pattern, eg Seq("*", "*"), to include and exclude respectively.

  • inferHtmlResources(white: WhiteList): fetch all resources matching a pattern in the white list.
  • inferHtmlResources(white: WhiteList, black: BlackList): fetch all resources matching a pattern in the white list excepting those in the black list.
  • inferHtmlResources(black: BlackList): fetch all resources excepting those matching a pattern in the black list.
  • inferHtmlResources(black: BlackList, white: WhiteList): fetch all resources excepting those matching a pattern in the black list and not in the white list.
  • inferHtmlResources(filters: Option[Filters])

Finally, you can specify the strategy for naming those requests in the reports:

  • nameInferredHtmlResourcesAfterUrlTail(default): name requests after the resource’s url tail (after last /)
  • nameInferredHtmlResourcesAfterPath: name requests after the resource’s path
  • nameInferredHtmlResourcesAfterAbsoluteUrl: name requests after the resource’s absolute url
  • nameInferredHtmlResourcesAfterRelativeUrl: name requests after the resource’s relative url
  • nameInferredHtmlResourcesAfterLastPathElement: name requests after the resource’s last path element
  • nameInferredHtmlResources(f: Uri => String): name requests with a custom strategy

Proxy parameters

You can tell Gatling to use a proxy to send the HTTP requests. You can optionally set a different port for HTTPS and credentials:

val httpProtocol = http
    Proxy("myHttpProxyHost", 8080)
      .credentials("myUsername", "myPassword")
    Proxy("mySocks4ProxyHost", 8080).socks4
    Proxy("mySocks5ProxyHost", 8080)

You can also disable the use of proxy for a given list of hosts with noProxyFor(hosts: String*):

val httpProtocol = http
  .proxy(Proxy("myProxyHost", 8080))
  .noProxyFor("", "")

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