Rate-limiting Guzzle Requests in Symfony - php

Question

This actually follows on from a previous question I had that, unfortunately, did not receive any answers so I'm not exactly holding my breath for a response but I understand this can be a bit of a tricky issue to solve.
I am currently trying to implement rate limiting on outgoing requests to an external API to match the limit on their end. I have tried to implement a token bucket library (https://github.com/bandwidth-throttle/token-bucket) into the class we are using to manage Guzzle requests for this particular API.
Initially, this seemed to be working as intended but we have now started seeing 429 responses from the API as it no longer seems to be correctly rate limiting the requests.
I have a feeling what is happening is that the number of tokens in the bucket is now being reset every time the API is called due to how Symfony handles services.
I am setting currently setting up the bucket location, rate and starting amount in the service's constructor:
public function __construct()
{
$storage = new FileStorage(__DIR__ . "/api.bucket");
$rate = new Rate(50, Rate::MINUTE);
$bucket = new TokenBucket(50, $rate, $storage);
$this->consumer = new BlockingConsumer($bucket);
$bucket->bootstrap(50);
}
I'm then attempting to consume a token before each request:
public function fetch(): array
{
try {
$this->consumer->consume(1);
$response = $this->client->request(
'GET', $this->buildQuery(), [
'query' => array_merge($this->params, ['api_key' => $this->apiKey]),
'headers' => [ 'Content-type' => 'application/json' ]
]
);
} catch (ServerException $e) {
// Process Server Exception
} catch (ClientException $e) {
// Process Client Exception
}
return $this->checkResponse($response);
}
I can't see anything obvious in that, that would allow it to request more than 50 times per minute unless the amount of available tokens was being reset on each request.
This is being supplied to a set of repository services that handle converting the data from each endpoint into objects used within the system. Consumers use the appropriate repository to request the data needed to complete their process.
If the amount of tokens is being reset by the bootstrap function being in service constructor, where should it be moved to within the Symfony framework that would still work with consumers?

Answer 1

I assume that it should work, but maybe try to move the ->bootstrap(50) call from every request? Not sure, but it can be the reason.
Anyway it's better to do that only once, as a part of your deployment (every time you deploy a new version). It doesn't have anything with Symfony, really, because the framework doesn't have any restrictions on deployment procedure. So it depends on how you do the deployment.
P.S. Have you considered to just handle 429 errors from the server? IMO you can wait (that's what BlockingConsumer does inside) when you receive 429 error. It's simpler and doesn't require an additional layer in your system.

Answer 2

BTW, have you considered nginx's ngx_http_limit_req_module as an alternative solution? It usually comes with nginx by default, so no additional actions to install, only a small configuration is required.
You can place an nginx proxy behind your code and the target web service and enable limits on it. Then in your code you will handle 429 as usual, but the requests will be throttled by your local nginx proxy, not by the external web service. So the final destination will get only limited amount of requests.

Answer 3

I have found a trick using Guzzle bundle for symfony.
I had to improve a sequential program sending GET requests to a Google API. In code example, it a pagespeed URL.
To have a rate limit, there an option to delay the requests before they are sent asynchronously.
Pagespeed rate limit is 200 requests per minute.
A quick calculation gives 200/60 = 0.3s per request.
Here is the code I tested on 300 urls, getting a fantastic result of no error, except if the url passed as a parameter in the GET request gives a 400 HTTP Error (Bad request).
I put a delay of 0.4s and the average result time is less then 0.2s, whereas it took more than a minute with a sequential program.
use GuzzleHttp;
use GuzzleHttp\Client;
use GuzzleHttp\Promise\EachPromise;
use GuzzleHttp\Exception\ClientException;
// ... Now inside class code ... //
$client = new GuzzleHttp\Client();
$promises = [];
foreach ($requetes as $i=>$google_request) {
$promises[] = $client->requestAsync('GET', $google_request ,['delay'=>0.4*$i*1000]); // delay is the trick not to exceed rate limit (in ms)
}
GuzzleHttp\Promise\each_limit($promises, function(){ // function returning the number of concurrent requests
return 100; // 1 or 100 concurrent request(s) don't really change execution time
}, // Fulfilled function
function ($response,$index)use($urls,$fp) { // $urls is used to get the url passed as a parameter in GET request and $fp a csv file pointer
$feed = json_decode($response->getBody(), true); // Get array of results
$this->write_to_csv($feed,$fp,$urls[$index]); // Write to csv
}, // Rejected function
function ($reason,$index) {
if ($reason instanceof GuzzleHttp\Exception\ClientException) {
$message = $reason->getMessage();
var_dump(array("error"=>"error","id"=>$index,"message"=>$message)); // You could write the errors to a file or database too
}
})->wait();