vegeta-sine

For those times when you want to hit a service hard, and then you don't, and then you do. Et cetera. Useful for seeing if autoscaling is working as it should.

Here's a picture of the requests per second as two instances of vegeta-sine hit a service with mean and amplitude of 15±5/s and 10±5/s respectively.

Building

go build

Or if you want to be sure it'll work on Linux or indeed inside a Docker container, you might use:

CGO_ENABLED=0 GOOS=linux go build -a -ldflags '-s'

Running

Vegeta-sine expects the list of targets in JSON format, via stdin. The documentation for this format can be found at the Vegeta repository: https://github.com/tsenart/vegeta#json-format. Note that it's JSON lines, not an array or whatever.

You'll want to decide the parameters of the sine wave you want to hit the targets with. The best description appears to be here: https://github.com/tsenart/vegeta/blob/d73edf2bc2663d83848da2a97a8401a7ed1440bc/lib/pacer.go#L101-L132

The short version is that vegeta-sine will vary the number of requests per second in the shape of a sine wave, in the range mean ± amplitude. Therefore, remember to make amplitude positive, and smaller than the mean (because a negative number of requests a second, well, that'd be weird). The period parameter defines the "width" of the sine wave, or how frequently it oscillates. Finally, the startAt parameter is useful if you know exactly the phase offset you want to start the oscillator at.

$ ./vegeta-sine --help
Usage of ./vegeta-sine:
  -amplitude int
    	The Amplitude in req/1s of the sine wave (default 1)
  -duration duration
    	Duration of the test in seconds
  -keepalive
    	Use persistent connections (default true)
  -mean int
    	The Mean req/1s of the sine wave (default 2)
  -period duration
    	Period of the sine wave (default 10m0s)
  -startAt float
    	The phase at which to start the sine wave, in radians
  -timeout duration
    	Requests timeout (default 30s)

Note that duration is a thing Golang will handle for you, so you can say things like 1m or 1h.

By default vegeta-sine will attack indefinitely, to avoid that you can pass -duration.

A real-life example

Over in haproxy-experiment you can see an example of how we used vegeta-sine. The important bits, to give you an idea of how to configure it:

vegeta-sine \
  -period="20m" \
  -mean="100" \
  -amplitude="50" \
  -startAt="${startAt}" \
  -keepalive=true \
  -timeout="12s" \
  < "${TARGETS_FILE}" \
  | vegeta encode \
  | jq ...

This will make vegeta-sine call the targets defined in ${TARGETS_FILE} (containing JSON lines) between 50 and 150 times per second. To understand how to work with the output, head to the official documentation.

A note on keeping many vegeta-sine workers in sync

You may want to keep separate vegeta-sine clients in sync. Here's a thing we used elsewhere:

minutesAfterHour=$(date +"%M")
startAt=$(echo "scale=5; pi=4*a(1); (${minutesAfterHour}/60)*2*pi" | bc -l)

This makes startAt, the phase offset of the sine wave, be the same for any worker started at that time. Handy!

Who? Why?

This is an SRE@Redbubble tool used to work out whether we were able to autoscale based on saturation metrics.