Throttling a Rest API in Java

Question

I wanted to add a way to throttle the number of requests coming on each API from a certain client. So, I wanted to basically limit the number of requests per API per client.

I am using DropWizard as framework. Can somebody recommend the ways to achieve this? I need something that will work for Distributed system.

Answer 1

A simplistic approach would be to use a Filter and wrap it around all your API calls in web.xml. Assuming your clients send an API keys identifying them in a HTTP header, you could implement a filter like this:

public class MyThrottlingFilter extends Filter {

    public void doFilter(ServletRequest req, ServletResponse res, FilterChain chain) throws IOException, ServletException {

        HttpServletRequest httpreq = (HttpServletRequest) req;
        String apiKey = httpreq.getHeader("API_KEY")

        if (invocationLimitNotReached(apiKey))
            chain.doFilter(req, res);
        else
            throw ...
    }
}

and then register it like this:

<filter>
    <filter-name>MyThrottlingFilter</filter-name>
    <filter-class>com.my.throttler.MyThrottlingFilter</filter-class>
</filter>
<filter-mapping>
    <filter-name>MyThrottlingFilter</filter-name>
    <url-pattern>/*</url-pattern>
</filter-mapping>

Of course, identifying your clients may be more difficult than this, if you use some other authentication methods, but the general idea should be the same.