Retry http requests in k6 - request

Question

I have a python requests-based suite of API tests that automatically retry every request with a 408 or 5xx response. I'm looking at re-implementing some of them in k6 for load testing. Does k6 have support for retrying http requests?

Answer 1

There is no such functionality in k6, but you can add it fairly simply by wrapping the k6/http functions like:
function httpGet(url, params) {
var res;
for (var retries = 3; retries > 0; retries--) {
res = http.get(url, params)
if (res.status != 408 && res.status < 500) {
return res;
}
}
return res;
}
And then just use httpGet instead of http.get ;)

Answer 2

You can create a reusable retry function and put it in a module to be imported by your test scripts.
The function can be general purpose:
Expect a function to retry
Expect a predicate to discern successful from failed calls
An upper retry limit
function retry(limit, fn, pred) {
while (limit--) {
let result = fn();
if (pred(result)) return result;
}
return undefined;
}
then provide the correct arguments when invoking:
retry(
3,
() => http.get('http://example.com'),
r => !(r.status == 408 || r.status >= 500));
Of course, feel free to wrap it in one or more, more specific, functions:
function get3(url) {
return request3(() => http.get(url));
}
function request3(req) {
return retry(
3,
req,
r => !(r.status == 408 || r.status >= 500));
}
let getResponse = get3('http://example.com');
let postResponse = request3(() => http.post(
'https://httpbin.org/post',
'body',
{ headers: { 'content-type': 'text/plain' } });
Bonus: you can make the calling code more expressive by implementing a cleverly named function, which inverts its result, instead of using the negation operator:
function when(pred) {
return x => !pred(x);
}
then
retry(
3,
() => http.get('http://example.com'),
when(r => r.status == 408 || r.status >= 500));
or turn around the behavior of the predicate altogether and test for failed requests instead for successful ones:
function retry(fn, pred, limit) {
while (limit--) {
let result = fn();
if (!pred(result)) return result;
}
return undefined;
}
function unless(pred) {
return x => !pred(x);
}
retry(
3,
() => http.get('http://example.com'),
r => r.status == 408 || r.status >= 500);
retry(
3,
() => http.get('http://example.com'),
unless(r => r.status != 408 && r.status < 500));