#async #testing #tcp #traffic #host #load #turn #tool #throw

bin+lib clobber

TCP load testing tool, written in async Rust

6 releases

0.3.0 Nov 5, 2019
0.2.2 Sep 9, 2019
0.2.1 Aug 21, 2019
0.1.1 Jul 3, 2019

24 downloads per month

MIT license

588 lines


clobber is a simple TCP load testing tool written in Rust. It can be a lot of work configuring a load test. clobber aims to simply throw a lot of traffic at a host, and much of the time that's all you need. clobber tries to deliver sensible defaults, and easy knobs to turn if you do need more advanced configuration.

clobber uses the async/await syntax, which currently requires the nightly branch, but is targeted to stabilize some time around the 1.39 release. This project was created as a way to kick the tires of the new syntax, since a network I/O heavy tool is a great use case for an async concurrency model.

My goal for this project is for the code to be performant, easy to read, and idiotmatic. If you see an area that is inefficient or confusing, I would happily welcome the feedback in an issue or PR.


# Only --target/-t is mandatory
echo "GET / HTTP/1.1\r\nHost: localhost:8000\r\n\r\n" | clobber --target=
# Other options can be provided via their own option flags. See Usage for full details.


# An easy pattern is to save a request to a file, and send it to clobber via the stdin pipe
cat my_request | clobber \
    --target=$TARGET \
    --connections=$CONNECTIONS \
    --duration=$DURATION \


clobber 0.1
tcp load testing tool

    clobber [FLAGS] [OPTIONS] --target <target>

    -h, --help       Prints help information
    -v               Sets the log level, from -v to -vvv
    -V, --version    Prints version information

        --connect-timeout <connect-timeout>    Timeout for initial TCP syn timeout
    -c, --connections <connections>            Max number of open connections at any given time
    -d, --duration <duration>                  Length of the run (e.g. 5s, 10m, 2h, etc...)
    -l, --limit <limit>                        Total number of requests
        --rate <rate>                          Limit to a particular rate per-second.
        --read-timeout <read-timeout>          Timeout for reading response from target
    -t, --target <target>                      Host to clobber
        --threads <threads>                    Number of threads

Troubleshooting TCP Performance

Open file limits

A common cause of TCP throughput issues is number of open files. You can check this with ulimit -n. If you're seeing issues with number of open files you can raise this limit with ulimit. If that doesn't work, you may need to edit /etc/security/limits.conf to raise the limit for your account.

Connection timeouts

The initial syn phase in the TCP handshake has a long timeout; often in the hundreds of seconds. This is controlled in /proc/sys/net/ipv4/tcp_syn_retries, but even if you set this to a low number a single timeout can take a long time. This mostly isn't an issue with the intended use case of testing locally running servers with clobber, but if your handshake is unreliable you can try configuring the connect-timeout option.

Read timeouts

Knowing when to stop reading from a TCP stream is tricky if you don't know how much data you should read. This is protocol dependent, and clobber has no idea. If the server doesn't send an EOF you can get stuck waiting for more data for a long time, and this can block connections. With some protocols (such as HTTP) you can send a header like Connection: close that signals to the host that you won't be sending any more requests, and that they should send an EOF after they've responded. This can fix throughput issues against some HTTP servers. If this isn't possible you should configure the read-timeout, but this does have a bit of an impact on top-end performance (especially with a high number of connections.)


~133K SLoC