Custom WRK (https://github.com/wg/wrk) script to count a response header useful for A/B load testing

README.md

Example

wrk -t 5 -c 10 -d 10s -s wrk-hostname-counter.lua https://example.com/

 ------------------------------------------------
 server-b-pxchg: 50.3333% (151 total)
 server-a-n82cc: 3.33333% (10 total)
 server-a-lr665: 3.33333% (10 total)
 server-a-7cnws: 3.33333% (10 total)
 server-a-m8lgc: 3.33333% (10 total)
 server-a-z58k9: 3.33333% (10 total)
 server-a-sqp99: 3.33333% (10 total)
 server-a-rwmx7: 3.33333% (10 total)
 server-a-d6f9r: 3.33333% (10 total)
 server-a-vncjc: 3.33333% (10 total)
 server-a-727vt: 3.33333% (10 total)
 server-a-j5m59: 3.33333% (10 total)
 server-a-lz55z: 3.33333% (10 total)
 server-a-pqt5x: 3.33333% (10 total)
 server-a-n8c6d: 3.33333% (10 total)
 server-a-b5ltb: 3% (9 total)

wrk-hostname-counter.lua

local threads = {}

function setup(thread)
    table.insert(threads, thread)
end

function init(args)
    hostnames = {}
end

function response(status, headers, body)
    local hostname = headers["X-Hostname"]

    if not hostnames[hostname] then hostnames[hostname] = 0 end
    hostnames[hostname] = hostnames[hostname] + 1
end

function done(summary, latency, requests)
    mergedHostnames = {}

    for _, thread in ipairs(threads) do
        local hostnames = thread:get("hostnames")

        for h, c in pairs(hostnames) do
            if not mergedHostnames[h] then mergedHostnames[h] = 0 end
            mergedHostnames[h] = mergedHostnames[h] + c
        end
    end

    print("---------------------------------\n")
    for h, c in pairs(mergedHostnames) do
        print((" %s: %g%% (%d total)"):format(h, (c / summary.requests) * 100, c))
    end
end