Hey all, I wanted to enforce an SLA on certain http requests to apache. Essentially provide a the external client users an guarantee that a valid response will be given within XXms and all errors are suppressed. This is for an ReST API that returns JSON or XML data.
Ronald Park attempted to do something similar for Apache 2.0 in Feb 2008 here: http://bit.ly/HglyS The issues with making apache do this are as follows: * ProxyTimeout is global or scoped to the particular vhost * ErrorDocuments still return the error code (503, 404, etc) * No way to tie ErrorDocuments and ProxyTimeouts to particular requests. I followed Ronald's lead and reimplemented in apache 2.2 with a few new additions. The below example is a rewrite rule that makes no changes to the URL itself for a JS API presumably returning data in JSON. RewriteRule ^/api/(.*).js\?*(.*)$ http://backendproxy/api/$1.js?$2 [P,QSA,E=proxy-timeout:900ms,E=error-suppress:true,E=error-headers:/errorapi.js.HTTP,E=error-document:/errorapi.js] With the SLA enforcement modifications enabled, the URL will return data from the backend system within 900ms or a timeout occurs. At this point apache will stop waiting for the backend response and serve back the static files /errorapi.js.HTTP as HTTP headers and /errorapi.js as contents. $cat /var/www/html/errorapi.js.HTTP Status: 204 Content-type: application/javascript $cat /var/www/html/errorapi.js var xxx_api_data={data:[]}; /* ERR */ There are four environment variables the SLA hack looks for: * proxy-timeout: - time in seconds or milliseconds to wait until timing out * error-suppress: - true/false switch on suppressing all non 2xx errors from the backend. * error-headers: - file of syntax correct HTTP headers to return to the client * error-document: - file of content body to be returned to the client Leaving off the proxy-timeout will only suppress errors from the backend after the global timeout occurs. Leaving off error-suppress:true will ensure that the 5xx timeout error from mod_proxy_http is returned intact to the client. Code here: http://github.com/nealrichter/mod_proxy_http_sla/tree Diff here: http://bit.ly/UdAHB Blog Post: http://aicoder.blogspot.com/2009/07/hacking-apaches-modproxyhttp-to-enforce.html Please examine and comment.. it's on production servers handling approx of 50Million API hits per day.. no issues thus far. I'd like some feedback if I'm resetting the timeout back to the previous one on the socket correctly and if there is a better way to do this in the code. I essentially used Ronald's code plus some stuff from mod_asis. Thanks - Neal Richter
