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#11 in Web programming

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Have you ever been attacked by a goose?

crates.io Documentation Apache-2.0 licensed CI Docker Repository on Quay


Goose is a Rust load testing tool inspired by Locust. User behavior is defined with standard Rust code. Load tests are applications that have a dependency on the Goose library. Web requests are made with the Reqwest HTTP Client.



Getting Started

The in-line documentation offers much more detail about Goose specifics. For a general background to help you get started with Rust and Goose, read on.

Cargo is the Rust package manager. To create a new load test, use Cargo to create a new application (you can name your application anything, we've generically selected loadtest):

$ cargo new loadtest
     Created binary (application) `loadtest` package
$ cd loadtest/

This creates a new directory named loadtest/ containing loadtest/Cargo.toml and loadtest/src/main.rs. Start by editing Cargo.toml adding Goose under the dependencies heading:

goose = "^0.11"

At this point it's possible to compile all dependencies, though the resulting binary only displays "Hello, world!":

$ cargo run
    Updating crates.io index
  Downloaded goose v0.11.2
   Compiling goose v0.11.2
   Compiling loadtest v0.1.0 (/home/jandrews/devel/rust/loadtest)
    Finished dev [unoptimized + debuginfo] target(s) in 52.97s
     Running `target/debug/loadtest`
Hello, world!

To create an actual load test, you first have to add the following boilerplate to the top of src/main.rs to make Goose's functionality available to your code:

use goose::prelude::*;

Then create a new load testing function. For our example we're simply going to load the front page of the website we're load-testing. Goose passes all load testing functions a pointer to a GooseUser object, which is used to track metrics and make web requests. Thanks to the Reqwest library, the Goose client manages things like cookies, headers, and sessions for you. Load testing functions must be declared async, which helps ensure that your simulated users don't become CPU-locked.

In load test functions you typically do not set the host, and instead configure the host at run time, so you can easily run your load test against different environments without recompiling. The following loadtest_index function simply loads the front page of our web page:

async fn loadtest_index(user: &GooseUser) -> GooseTaskResult {
    let _goose_metrics = user.get("/").await?;


The function is declared async so that we don't block a CPU-core while loading web pages. All Goose load test functions are passed in a reference to a GooseUser object, and return a GooseTaskResult which is either an empty Ok(()) on success, or a GooseTaskError on failure. We use the GooseUser object to make requests, in this case we make a GET request for the front page, /. The .await frees up the CPU-core while we wait for the web page to respond, and the tailing ? passes up any unexpected errors that may be returned from this request. When the request completes, Goose returns metrics which we store in the _goose_metrics variable. The variable is prefixed with an underscore (_) to tell the compiler we are intentionally not using the results. Finally, after making a single successful request, we return Ok(()) to let Goose know this task function completed successfully.

We have to tell Goose about our new task function. Edit the main() function, setting a return type and replacing the hello world text as follows:

fn main() -> Result<(), GooseError> {

If you're new to Rust, main()'s return type of Result<(), GooseError> may look strange. It essentially says that main will return nothing (()) on success, and will return a GooseError on failure. This is helpful as several of GooseAttack's methods can fail, returning an error. In our example, initialize() and execute() each may fail. The ? that follows the method's name tells our program to exit and return an error on failure, otherwise continue on. The print() method consumes the GooseMetrics object returned by GooseAttack.execute() and prints a summary if metrics are enabled. The final line, Ok(()) returns the empty result expected on success.

And that's it, you've created your first load test! Let's run it and see what happens.

$ cargo run
   Compiling loadtest v0.1.0 (/home/jandrews/devel/rust/loadtest)
    Finished dev [unoptimized + debuginfo] target(s) in 3.56s
     Running `target/debug/loadtest`
Error: InvalidOption { option: "--host", value: "", detail: "A host must be defined via the --host option, the GooseAttack.set_default() function, or the GooseTaskSet.set_host() function (no host defined for LoadtestTasks)." }

Goose is unable to run, as it hasn't been told the host you want to load test. So, let's try again, this time passing in the --host flag. After running for a few seconds, we then press ctrl-c to stop the load test:

$ cargo run -- --host http://local.dev/
    Finished dev [unoptimized + debuginfo] target(s) in 0.07s
     Running `target/debug/loadtest --host 'http://local.dev/'`

 Name                    | # times run    | # fails        | task/s | fail/s
 1: LoadtestTasks        |
   1:                    | 2,240          | 0 (0%)         | 280.0  | 0.000
 Name                    | Avg (ms)   | Min        | Max        | Median    
 1: LoadtestTasks        |
   1:                    | 15.54      | 6          | 136        | 14        

 Name                    | # reqs         | # fails        | req/s  | fail/s
 GET /                   | 2,240          | 0 (0%)         | 280.0  | 0.000
 Name                    | Avg (ms)   | Min        | Max        | Median    
 GET /                   | 15.30      | 6          | 135        | 14        

All 8 users hatched, resetting metrics (disable with --no-reset-metrics).

^C06:03:25 [ WARN] caught ctrl-c, stopping...

 Name                    | # times run    | # fails        | task/s | fail/s
 1: LoadtestTasks        |
   1:                    | 2,054          | 0 (0%)         | 410.8  | 0.000
 Name                    | Avg (ms)   | Min        | Max        | Median    
 1: LoadtestTasks        |
   1:                    | 20.86      | 7          | 254        | 19        

 Name                    | # reqs         | # fails        | req/s  | fail/s
 GET /                   | 2,054          | 0 (0%)         | 410.8  | 0.000
 Name                    | Avg (ms)   | Min        | Max        | Median    
 GET /                   | 20.68      | 7          | 254        | 19        
 Slowest page load within specified percentile of requests (in ms):
 Name                    | 50%    | 75%    | 98%    | 99%    | 99.9%  | 99.99%
 GET /                   | 19     | 21     | 53     | 69     | 250    | 250   

By default, Goose will hatch 1 GooseUser per second, up to the number of CPU cores available on the server used for load testing. In the above example, the server has 8 CPU cores, so it took 8 seconds to hatch all users. After all users are hatched, Goose flushes all metrics collected during the hatching process so all subsequent metrics are taken with all users running. Before flushing the metrics, they are displayed to the console so the data is not lost.

The same metrics are displayed per-task and per-request. In our simple example, our single task only makes one request, so in this case both metrics show the same results.

The per-task metrics are displayed first, starting with the name of our Task Set, LoadtestTasks. Individual tasks in the Task Set are then listed in the order they are defined in our load test. We did not name our task, so it simply shows up as 1: . All defined tasks will be listed here, even if they did not run, so this can be useful to confirm everything in your load test is running as expected.

Next comes the per-request metrics. Our single task makes a GET request for the / path, so it shows up in the metrics as GET /. Comparing the per-task metrics collected for 1: to the per-request metrics collected for GET /, you can see that they are the same.

There are two common tables found in each type of metrics. The first shows the total number of requests made (2,054), how many of those failed (0), the average number of requests per second (410.8), and the average number of failed requests per second (0).

The second table shows the average time required to load a page (20.68 milliseconds), the minimum time to load a page (7 ms), the maximum time to load a page (254 ms) and the median time to load a page (19 ms).

The per-request metrics include a third table, showing the slowest page load time for a range of percentiles. In our example, in the 50% fastest page loads, the slowest page loaded in 19 ms. In the 75% fastest page loads, the slowest page loaded in 21 ms, etc.

In real load tests, you'll most likely have multiple task sets each with multiple tasks, and Goose will show you metrics for each along with an aggregate of them all together.

Refer to the examples directory for more complicated and useful load test examples.


  • Avoid unwrap() in your task functions -- Goose generates a lot of load, and this tends to trigger errors. Embrace Rust's warnings and properly handle all possible errors, this will save you time debugging later.
  • When running your load test for real, use the cargo --release flag to generate optimized code. This can generate considerably more load test traffic.

Simple Example

The -h flag will show all run-time configuration options available to Goose load tests. For example, you can pass the -h flag to the simple example as follows, cargo run --example simple -- -h:

Usage: target/debug/examples/simple [OPTIONS]

Options available when launching a Goose load test.

Optional arguments:
  -h, --help                 Displays this help
  -V, --version              Prints version information
  -l, --list                 Lists all tasks and exits

  -H, --host HOST            Defines host to load test (ie
  -u, --users USERS          Sets concurrent users (default: number of CPUs)
  -r, --hatch-rate RATE      Sets per-second user hatch rate (default: 1)
  -t, --run-time TIME        Stops after (30s, 20m, 3h, 1h30m, etc)
  -g, --log-level            Sets log level (-g, -gg, etc)
  -L, --log-file NAME        Enables log file and sets name
  -v, --verbose              Sets debug level (-v, -vv, etc)

  --running-metrics TIME     How often to optionally print running metrics
  --no-reset-metrics         Doesn't reset metrics after all users have started
  --no-metrics               Doesn't track metrics
  --no-task-metrics          Doesn't track task metrics
  --no-error-summary         Doesn't display an error summary
  -R, --report-file NAME     Create an html-formatted report
  -m, --requests-file NAME   Sets requests log file name
  --requests-format FORMAT   Sets requests log format (csv, json, raw)
  -d, --debug-file NAME      Sets debug log file name
  --debug-format FORMAT      Sets debug log format (json, raw)
  --no-debug-body            Do not include the response body in the debug log
  --status-codes             Tracks additional status code metrics

  --no-telnet                Doesn't enable telnet Controller
  --telnet-host HOST         Sets telnet Controller host (default:
  --telnet-port PORT         Sets telnet Controller TCP port (default: 5116)
  --no-websocket             Doesn't enable WebSocket Controller
  --websocket-host HOST      Sets WebSocket Controller host (default:
  --websocket-port PORT      Sets WebSocket Controller TCP port (default: 5117)
  --no-autostart             Doesn't automatically start load test
  --throttle-requests VALUE  Sets maximum requests per second
  --sticky-follow            Follows base_url redirect with subsequent requests

  --manager                  Enables distributed load test Manager mode
  --expect-workers VALUE     Sets number of Workers to expect
  --no-hash-check            Tells Manager to ignore load test checksum
  --manager-bind-host HOST   Sets host Manager listens on (default:
  --manager-bind-port PORT   Sets port Manager listens on (default: 5115)
  --worker                   Enables distributed load test Worker mode
  --manager-host HOST        Sets host Worker connects to (default:
  --manager-port PORT        Sets port Worker connects to (default: 5115)

The examples/simple.rs example copies the simple load test documented on the locust.io web page, rewritten in Rust for Goose. It uses minimal advanced functionality, but demonstrates how to GET and POST pages. It defines a single Task Set which has the user log in and then load a couple of pages.

Goose can make use of all available CPU cores. By default, it will launch 1 user per core, and it can be configured to launch many more. The following was configured instead to launch 1,024 users. Each user randomly pauses 5 to 15 seconds after each task is loaded, so it's possible to spin up a large number of users. Here is a snapshot of top when running this example on a 1-core VM with 10G of available RAM -- there were ample resources to launch considerably more "users", though ulimit had to be resized:

top - 06:56:06 up 15 days,  3:13,  2 users,  load average: 0.22, 0.10, 0.04
Tasks: 116 total,   3 running, 113 sleeping,   0 stopped,   0 zombie
%Cpu(s):  1.7 us,  0.7 sy,  0.0 ni, 96.7 id,  0.0 wa,  0.0 hi,  1.0 si,  0.0 st
MiB Mem :   9994.9 total,   7836.8 free,   1101.2 used,   1056.9 buff/cache
MiB Swap:  10237.0 total,  10237.0 free,      0.0 used.   8606.9 avail Mem 

  PID USER      PR  NI    VIRT    RES    SHR S  %CPU  %MEM     TIME+ COMMAND    
 1339 goose     20   0 1235480 758292   8984 R   3.0   7.4   0:06.56 simple     

Here's the output of running the loadtest. The -v flag sends INFO and more critical messages to stdout (in addition to the log file). The -u1024 tells Goose to spin up 1,024 users. The -r32 option tells Goose to hatch 32 users per second. The -t10m option tells Goose to run the load test for 10 minutes, or 600 seconds. The --status-codes flag tells Goose to track metrics about HTTP status codes returned by the server, in addition to the default per-task and per-request metrics. The --no-reset-metrics flag tells Goose to start tracking the 10m run-time from when the first user starts, instead of the default which is to flush all metrics and start timing after all users have started. And finally, the --only-summary flag tells Goose to only display the final metrics after the load test finishes, otherwise it would display running metrics every 15 seconds for the duration of the test.

$ cargo run --release --example simple -- --host http://local.dev -v -u1024 -r32 -t10m --status-codes --no-reset-metrics --only-summary
    Finished release [optimized] target(s) in 0.09s
     Running `target/release/examples/simple --host 'http://local.dev' -v -u1024 -r32 -t10m --status-codes --no-reset-metrics --only-summary`
10:55:04 [ INFO] Output verbosity level: INFO
10:55:04 [ INFO] Logfile verbosity level: INFO
10:55:04 [ INFO] Writing to log file: goose.log
10:55:04 [ INFO] run_time = 600
10:55:04 [ INFO] global host configured: http://local.dev
10:55:04 [ INFO] initializing user states...
10:55:09 [ INFO] launching user 1 from WebsiteUser...
10:55:09 [ INFO] launching user 2 from WebsiteUser...
10:55:09 [ INFO] launching user 3 from WebsiteUser...


10:55:42 [ INFO] launching user 1022 from WebsiteUser...
10:55:42 [ INFO] launching user 1023 from WebsiteUser...
10:55:42 [ INFO] launching user 1024 from WebsiteUser...
10:55:42 [ INFO] launched 1024 users...
All 1024 users hatched.

11:05:09 [ INFO] stopping after 600 seconds...
11:05:09 [ INFO] waiting for users to exit
11:05:09 [ INFO] exiting user 879 from WebsiteUser...
11:05:09 [ INFO] exiting user 41 from WebsiteUser...
11:05:09 [ INFO] exiting user 438 from WebsiteUser...


11:05:10 [ INFO] exiting user 268 from WebsiteUser...
11:05:10 [ INFO] exiting user 864 from WebsiteUser...
11:05:10 [ INFO] exiting user 55 from WebsiteUser...
11:05:11 [ INFO] printing metrics after 601 seconds...

 Name                    | # times run    | # fails        | task/s | fail/s
 1: WebsiteUser          |
   1:                    | 1,024          | 0 (0%)         | 1.707  | 0.000
   2:                    | 28,746         | 0 (0%)         | 47.91  | 0.000
   3:                    | 28,748         | 0 (0%)         | 47.91  | 0.000
 Aggregated              | 58,518         | 0 (0%)         | 97.53  | 0.000
 Name                    | Avg (ms)   | Min        | Max        | Median    
 1: WebsiteUser          |
   1:                    | 5.995      | 5          | 37         | 6         
   2:                    | 0.428      | 0          | 17         | 0         
   3:                    | 0.360      | 0          | 37         | 0         
 Aggregated              | 0.492      | 5          | 37         | 5         

 Name                    | # reqs         | # fails        | req/s  | fail/s
 GET /                   | 28,746         | 0 (0%)         | 47.91  | 0.000
 GET /about/             | 28,748         | 0 (0%)         | 47.91  | 0.000
 POST /login             | 1,024          | 0 (0%)         | 1.707  | 0.000
 Aggregated              | 58,518         | 29,772 (50.9%) | 97.53  | 49.62
 Name                    | Avg (ms)   | Min        | Max        | Median    
 GET /                   | 0.412      | 0          | 17         | 0         
 GET /about/             | 0.348      | 0          | 37         | 0         
 POST /login             | 5.979      | 5          | 37         | 6         
 Aggregated              | 0.478      | 5          | 37         | 5         
 Slowest page load within specified percentile of requests (in ms):
 Name                    | 50%    | 75%    | 98%    | 99%    | 99.9%  | 99.99%
 GET /                   | 0      | 1      | 3      | 4      | 5      | 5     
 GET /about/             | 0      | 0      | 3      | 3      | 5      | 5     
 POST /login             | 6      | 6      | 7      | 7      | 28     | 28    
 Aggregated              | 5      | 5      | 5      | 6      | 7      | 17    
 Name                    | Status codes              
 GET /                   | 28,746 [200]             
 GET /about/             | 28,748 [200]             
 POST /login             | 1,024 [200]              
 Aggregated              | 58,518 [200]

Scheduling GooseTaskSets

When starting a load test, Goose assigns one GooseTaskSet to each GooseUser thread. By default, it assigns GooseTaskSets (and then GooseTasks within the task set) in a round robin order. As new GooseUser threads are launched, the first will be assigned the first defined GooseTaskSet, the next will be assigned the next defined GooseTaskSet, and so on, looping through all available GooseTaskSets. Weighting is respected during this process, so if one GooseTaskSet is weighted heavier than others, that GooseTaskSet will get assigned to GooseUsers more at the end of the launching process.

The GooseScheduler can be configured to instead launch GooseTaskSets and GooseTasks in a Serial or a Random order. When configured to allocate in a Serial order, GooseTaskSets and GooseTasks are launched in the extact order they are defined in the load test (see below for more detail on how this works). When configured to allocate in a Random order, running the same load test multiple times can lead to different amounts of load being generated.

Prior to Goose 0.10.6 GooseTaskSets were allocated in a serial order. Prior to Goose 0.11.1 GooseTasks were allocated in a serial order. To restore the old behavior, you can use the GooseAttack::set_scheduler() method as follows:


To instead randomize the order that GooseTaskSets and GooseTasks are allocated, you can instead configure as follows:


The following configuration is possible but superfluous because it is the scheduling default, and is therefor how Goose behaves even if the .set_scheduler() method is not called at all:


Scheduling Example

The following simple example helps illustrate how the different schedulers work.


Round Robin

This first example assumes the default of .set_scheduler(GooseScheduler::RoundRobin).

If Goose is told to launch only two users, the first GooseUser will run TaskSet1 and the second user will run TaskSet2. Even though TaskSet1 has a weight of 2 GooseUsers are allocated round-robin so with only two users the second instance of TaskSet1 is never launched.

The GooseUser running TaskSet1 will then launch tasks repeatedly in the following order: task1, task2, task1. If it runs through twice, then it runs all of the following tasks in the following order: task1, task2, task1, task1, task2, task1.


This second example assumes the manual configuration of .set_scheduler(GooseScheduler::Serial).

If Goose is told to launch only two users, then both GooseUsers will launch TaskSet1 as it has a weight of 2. TaskSet2 will not get assigned to either of the users.

Both GooseUsers running TaskSet1 will then launch tasks repeatedly in the following order: task1, task1, task2. If it runs through twice, then it runs all of the following tasks in the following order: task1, task1, task2, task1, task1, task2.


This third example assumes the manual configuration of .set_scheduler(GooseScheduler::Random).

If Goose is told to launch only two users, the first will be randomly assigned either TaskSet1 or TaskSet2. Regardless of which is assigned to the first user, the second will again be randomly assigned either TaskSet1 or TaskSet2. If the load test is stopped and run again, there users are randomly re-assigned, there is no consistency between load test runs.

Each GooseUser will run tasks in a random order. The random order will be determined at start time and then will run repeatedly in this random order as long as the user runs.


All run-time options can be configured with custom defaults. For example, you may want to default to the the host name of your local development environment, only requiring that --host be set when running against a production environment. Assuming your local development environment is at "http://local.dev/" you can do this as follows:

        .set_default(GooseDefault::Host, "http://local.dev/")?

The following defaults can be configured with a &str:

  • host: GooseDefault::Host
  • log file name: GooseDefault::LogFile
  • html-formatted report file name: GooseDefault::ReportFile
  • requests log file name: GooseDefault::RequestsFile
  • requests log file format: GooseDefault::RequestsFormat
  • debug log file name: GooseDefault::DebugFile
  • debug log file format: GooseDefault::DebugFormat
  • host to bind telnet Controller to: GooseDefault::TelnetHost
  • host to bind WebSocket Controller to: GooseDefault::WebSocketHost
  • host to bind Manager to: GooseDefault::ManagerBindHost
  • host for Worker to connect to: GooseDefault::ManagerHost

The following defaults can be configured with a usize integer:

  • total users to start: GooseDefault::Users
  • users to start per second: GooseDefault::HatchRate
  • how often to print running statistics: GooseDefault::RunningStatistics
  • number of seconds for test to run: GooseDefault::RunTime
  • log level: GooseDefault::LogLevel
  • verbosity: GooseDefault::Verbose
  • maximum requests per second: GooseDefault::ThrottleRequests
  • number of Workers to expect: GooseDefault::ExpectWorkers
  • port to bind telnet Controller to: GooseDefault::TelnetPort
  • port to bind WebSocket Controller to: GooseDefault::WebSocketPort
  • port to bind Manager to: GooseDefault::ManagerBindPort
  • port for Worker to connect to: GooseDefault::ManagerPort

The following defaults can be configured with a bool:

  • do not reset metrics after all users start: GooseDefault::NoResetMetrics
  • do not track metrics: GooseDefault::NoMetrics
  • do not track task metrics: GooseDefault::NoTaskMetrics
  • do not start telnet Controller thread: GooseDefault::NoTelnet
  • do not start WebSocket Controller thread: GooseDefault::NoWebSocket
  • do not autostart load test, wait instead for a Controller to start: GooseDefault::NoAutoStart
  • track status codes: GooseDefault::StatusCodes
  • follow redirect of base_url: GooseDefault::StickyFollow
  • enable Manager mode: GooseDefault::Manager
  • ignore load test checksum: GooseDefault::NoHashCheck
  • enable Worker mode: GooseDefault::Worker

For example, without any run-time options the following load test would automatically run against local.dev, logging metrics to goose-metrics.log and debug to goose-debug.log. It will automatically launch 20 users in 4 seconds, and run the load test for 15 minutes. Metrics will be displayed every minute during the test and will include additional status code metrics. The order the defaults are set is not important.

        .set_default(GooseDefault::Host, "local.dev")?
        .set_default(GooseDefault::RequestsFile, "goose-requests.log")?
        .set_default(GooseDefault::DebugFile, "goose-debug.log")?
        .set_default(GooseDefault::Users, 20)?
        .set_default(GooseDefault::HatchRate, 4)?
        .set_default(GooseDefault::RunTime, 900)?
        .set_default(GooseDefault::RunningStatistics, 60)?
        .set_default(GooseDefault::StatusCodes, true)?

Controlling Running Goose Load Test

By default, Goose will launch a telnet Controller thread that listens on, and a WebSocket Controller thread that listens on The running Goose load test can be controlled through these Controllers. Goose can optionally be started with the --no-autostart run time option to prevent the load test from automatically starting, requiring instead that it be started with a Controller command. When Goose is started this way, a host is not required and can instead be configured via the Controller.

NOTE: The controller currently is not Gaggle-aware, and only functions correctly when running Goose as a single process in standalone mode.

Telnet Controller

The host and port that the telnet Controller listens on can be configured at start time with --telnet-host and --telnet-port. The telnet Controller can be completely disabled with the --no-telnet command line option. The defaults can be changed with GooseDefault::TelnetHost,GooseDefault::TelnetPort, and GooseDefault::NoTelnet.

To learn about all available commands, telnet into the Controller thread and enter help (or ?), for example:

% telnet localhost 5116
Connected to localhost.
Escape character is '^]'.
goose> ?  
goose 0.11.2 controller commands:
 help (?)           this help
 exit (quit)        exit controller
 start              start an idle load test
 stop               stop a running load test and return to idle state
 shutdown           shutdown running load test (and exit controller)
 host HOST          set host to load test, ie http://localhost/
 users INT          set number of simulated users
 hatchrate FLOAT    set per-second rate users hatch
 runtime TIME       set how long to run test, ie 1h30m5s
 config             display load test configuration
 config-json        display load test configuration in json format
 metrics            display metrics for current load test
 metrics-json       display metrics for current load test in json format

WebSocket Controller

The host and port that the WebSocket Controller listens on can be configured at start time with --websocket-host and --websocket-port. The WebSocket Controller can be completely disabled with the --no-websocket command line option. The defaults can be changed with GooseDefault::WebSocketHost,GooseDefault::WebSocketPort, and GooseDefault::NoWebSocket.

The WebSocket Controller supports the same commands listed above. Requests and Response are in JSON format.

Requests must be made in the following format:

  "request": String, 

For example, a client should send the follow json to request the current load test metrics:

  "request": "metrics", 

Responses will always be in the following format:

  "response": String,
  "success": Boolean,

For example:

% websocat ws://
{"response":"unable to parse json, see Goose README.md","success":false}
{"request": "foo"}
{"response":"unrecognized command, see Goose README.md","success":false}
{"request": "config"}
{"request": "stop"}
{"response":"load test not running, failed to stop","success":false}
{"request": "exit"}

Throttling Requests

By default, Goose will generate as much load as it can. If this is not desirable, the throttle allows optionally limiting the maximum number of requests per second made during a load test. This can be helpful to ensure consistency when running a load test from multiple different servers with different available resources.

The throttle is specified as an integer. For example:

$ cargo run --example simple -- --host http://local.dev/ -u100 -r20 -v --throttle-requests 5

In this example, Goose will launch 100 GooseUser threads, but the throttle will prevent them from generating a combined total of more than 5 requests per second. The --throttle-requests command line option imposes a maximum number of requests, not a minimum number of requests.

Logging Load Test Requests

Goose can optionally log details about all load test requests to a file. To enable, add the --requests-file=foo command line option, where foo is either a relative or absolute path of the log file to create. Any existing file that may already exist will be overwritten.

When operating in Gaggle-mode, the --requests--file option can only be enabled on the Worker processes, configuring Goose to spread out the overhead of writing logs.

By default, logs are written in JSON Lines format. For example:


Logs include the entire GooseRawRequest object as defined in src/goose.rs, which are created on all requests. This object includes the following fields:

  • elapsed: total milliseconds between when the GooseUser thread started and this request was made;
  • method: the type of HTTP request made;
  • name: the name of the request;
  • url: the URL that was requested;
  • final_url: the URL that was returned (may be different if the request was redirected);
  • redirected: true or false if the request was redirected;
  • response_time: how many milliseconds the request took;
  • status_code: the HTTP response code returned for this request;
  • success: true or false if this was a successful request;
  • update: true or false if this is a recurrence of a previous log entry, but with success toggling between true and false. This happens when a load test calls set_success() on a request that Goose previously interpreted as a failure, or set_failure() on a request previously interpreted as a success;
  • user: an integer value indicating which GooseUser thread made this request.

In the first line of the above example, GooseUser thread 0 made a POST request to /login and was successfully redirected to /user/42 in 220 milliseconds. The second line is the same GooseUser thread which then made a GET request to / in 3 milliseconds. The third and fourth lines are a second GooseUser thread doing the same thing, first logging in and then loading the front page.

By default Goose logs requests in JSON Lines format. The --metrics-log-format option can be used to log in csv, json or raw format. The raw format is Rust's debug output of the entire GooseRawRequest object.

For example, csv output of the same requests logged above would look like:


Load Test Debug Logging

Goose can optionally and efficiently log arbitrary details, and specifics about requests and responses for debug purposes. A central logging thread maintains a buffer to minimize the IO overhead, and controls the writing to ensure that multiple threads don't corrupt each other's messages.

To write to the debug log, you must invoke client.log_debug(tag, Option<request>, Option<headers>, Option<body>) from your load test task functions. The tag field is required and can be any arbitrary string: it can identify where in the load test the log was generated, and/or why debug is being written, and/or other details such as the contents of a form the load test posts. The request field is an optional reference to the GooseRawRequest object and provides details such as what URL was requested and if it redirected, how long into the load test the request was made, which GooseUser thread made the request, and what status code the server responded with. The headers field is an optional reference to all the HTTP headers returned by the remote server for this request. The body field is an optional reference to the entire web page body returned by the server for this request.

See examples/drupal_loadtest for an example of how you might invoke log_debug from a load test.

Calls to client.set_failure(tag, Option<request>, Option<headers>, Option<body>) can be used to tell Goose that a request failed even though the server returned a successful status code, and will automatically invoke log_debug() for you. See examples/drupal_loadtest and examples/umami to see how you might use set_failure to generate useful debug logs.

When the load test is run with the --debug-file=foo command line option, where foo is either a relative or an absolute path, Goose will log all debug generated by calls to client.log_debug() (or to client.set_failure()) to this file. If the file already exists it will be overwritten. The following is an example debug log file entry:

{"body":"<!DOCTYPE html>\n<html>\n  <head>\n    <title>503 Backend fetch failed</title>\n  </head>\n  <body>\n    <h1>Error 503 Backend fetch failed</h1>\n    <p>Backend fetch failed</p>\n    <h3>Guru Meditation:</h3>\n    <p>XID: 923425</p>\n    <hr>\n    <p>Varnish cache server</p>\n  </body>\n</html>\n","header":"{\"date\": \"Wed, 01 Jul 2020 10:27:31 GMT\", \"server\": \"Varnish\", \"content-type\": \"text/html; charset=utf-8\", \"retry-after\": \"5\", \"x-varnish\": \"923424\", \"age\": \"0\", \"via\": \"1.1 varnish (Varnish/6.1)\", \"x-varnish-cache\": \"MISS\", \"x-varnish-cookie\": \"SESSd7e04cba6a8ba148c966860632ef3636=hejsW1mQnnsHlua0AicCjEpUjnCRTkOLubwL33UJXRU\", \"content-length\": \"283\", \"connection\": \"keep-alive\"}","request":{"elapsed":4192,"final_url":"http://local.dev/node/3247","method":"GET","name":"(Auth) comment form","redirected":false,"response_time":8,"status_code":503,"success":false,"update":false,"url":"http://local.dev/node/3247","user":4},"tag":"post_comment: no form_build_id found on node/3247"}

If --debug-file=foo is not specified at run time, nothing will be logged and there is no measurable overhead in your load test.

By default Goose writes debug logs in JSON Lines format. The --debug-format option can be used to log in json or raw format. The raw format is Rust's debug output of the GooseDebug object.

Gaggle: Distributed Load Test

Goose also supports distributed load testing. A Gaggle is one Goose process running in Manager mode, and 1 or more Goose processes running in Worker mode. The Manager coordinates starting and stopping the Workers, and collects aggregated metrics. Gaggle support is a cargo feature that must be enabled at compile-time as documented below. To launch a Gaggle, you must copy your load test application to all servers from which you wish to generate load.

It is strongly recommended that the same load test application be copied to all servers involved in a Gaggle. By default, Goose will verify that the load test is identical by comparing a hash of all load test rules. Telling it to skip this check can cause the load test to panic (for example, if a Worker defines a different number of tasks or task sets than the Manager).

Gaggle Compile-time Feature

Gaggle support is a compile-time Cargo feature that must be enabled. Goose uses the nng library to manage network connections, and compiling nng requires that cmake be available.

The gaggle feature can be enabled from the command line by adding --features gaggle to your cargo command.

When writing load test applications, you can default to compiling in the Gaggle feature in the dependencies section of your Cargo.toml, for example:

goose = { version = "^0.11", features = ["gaggle"] }

Gaggle Manager

To launch a Gaggle, you first must start a Goose application in Manager mode. All configuration happens in the Manager. To start, add the --manager flag and the --expect-workers flag, the latter necessary to tell the Manager process how many Worker processes it will be coordinating. For example:

cargo run --features gaggle --example simple -- --manager --expect-workers 2 --host http://local.dev/ -v

This configures a Goose Manager to listen on all interfaces on the default port ( for 2 Goose Worker processes.

Gaggle Worker

At this time, a Goose process can be either a Manager or a Worker, not both. Therefor, it usually makes sense to launch your first Worker on the same server that the Manager is running on. If not otherwise configured, a Goose Worker will try to connect to the Manager on the localhost. This can be done as follows:

cargo run --features gaggle --example simple -- --worker -v

In our above example, we expected 2 Workers. The second Goose process should be started on a different server. This will require telling it the host where the Goose Manager process is running. For example:

cargo run --example simple -- --worker --manager-host -v

Once all expected Workers are running, the distributed load test will automatically start. We set the -v flag so Goose provides verbose output indicating what is happening. In our example, the load test will run until it is canceled. You can cancel the Manager or either of the Worker processes, and the test will stop on all servers.

Gaggle Run-time Flags

  • --manager: starts a Goose process in Manager mode. There currently can only be one Manager per Gaggle.
  • --worker: starts a Goose process in Worker mode. How many Workers are in a given Gaggle is defined by the --expect-workers option, documented below.
  • --no-hash-check: tells Goose to ignore if the load test application doesn't match between Worker(s) and the Manager. This is not recommended, and can cause the application to panic.

The --no-metrics, --only-summary, --no-reset-metrics, --status-codes, and --no-hash-check flags must be set on the Manager. Workers inherit these flags from the Manager

Gaggle Run-time Options

  • --manager-bind-host <manager-bind-host>: configures the host that the Manager listens on. By default Goose will listen on all interfaces, or
  • --manager-bind-port <manager-bind-port>: configures the port that the Manager listens on. By default Goose will listen on port 5115.
  • --manager-host <manager-host>: configures the host that the Worker will talk to the Manager on. By default, a Goose Worker will connect to the localhost, or In a distributed load test, this must be set to the IP of the Goose Manager.
  • --manager-port <manager-port>: configures the port that a Worker will talk to the Manager on. By default, a Goose Worker will connect to port 5115.

The --users, --hatch-rate, --host, and --run-time options must be set on the Manager. Workers inherit these options from the Manager.

The --throttle-requests option must be configured on each Worker, and can be set to a different value on each Worker if desired.

Technical Details

Goose uses nng to send network messages between the Manager and all Workers. Serde and Serde CBOR are used to serialize messages into Concise Binary Object Representation.

Workers initiate all network connections, and push metrics to the Manager process.


By default Reqwest (and therefore Goose) uses the system-native transport layer security to make HTTPS requests. This means schannel on Windows, Security-Framework on macOS, and OpenSSL on Linux. If you'd prefer to use a pure Rust TLS implementation, disable default features and enable rustls in Cargo.toml as follows:

goose = { version = "^0.11", default-features = false, features = ["rustls"] }


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