• 201509.05

    Nginx returns error on file upload

    I love Nginx and have never had a problem with it. Until now.

    Turtl, the private Evernote alternative, allows uploading files securely. However, after switching to a new server on Linode, uploads broke for files over 10K. The server was returning a 404.

    I finally managed to reproduce the problem in cURL, and to my surprise, the requests were getting stopped by Nginx. All other requests were going through fine, and the error only happened when uploading a file of 10240 bytes or more.

    First thing I though was that Nginx v1.8.0 had a bug. Nobody on the internet seemed to have this problem. So I installed v1.9.4. Now the server returned a 500 error instead of a 404. Still no answer to why.

    I finally found it: playing with client_body_buffer_size seemed to change the threshold for which files would trigger the error and which wouldn’t, but ultimately the error was still there. Then I read about how Nginx uses temporary files to store body data. I checked that folder (in my case /var/lib/nginx/client_body) and the folder was writeable by the nginx user, however the parent folder /var/lib/nginx was owned by root:root and was set to 0700. I set /var/lib/nginx to be readable/writable by user nginx, and it all started working.

    Check your permissions

    So, check your folder permissions. Nginx wasn’t returning any useful errors (first a 404, which I’m assuming was a bug fixed in a later version) then a 500 error. It’s important to note that after switching to v1.9.4, the Permission Denied error did show up in the error log, but at that point I had already decided the logs were useless (v1.8.0 silently ignored the problem).

    Another problem

    This is an edit! Shortly after I applied the above fix, I started getting another error. My backend was getting the requests, but the entire request was being buffered by Nginx before being proxied. This is annoying to me because the backend is async and is made to stream large uploads.

    After some research, I found the fix (I put this in the backend proxy’s location block:

    proxy_request_buffering off;

    This tells Nginx to just stream the request to the backend (exactly what I want).

  • 201005.03

    Using gzip_static in nginx to cache gzip files

    Recently I've been working on speeding up the homepage of beeets.com. Most speed tests say it takes between 4-6 seconds. Obviously, all of them are somehow fatally flawed. I digress, though.

    Everyone (who's anyone) knows that gzipping your content is a great way to reduce download time for your users. It can cut the size of html, css, and javascript by about 60-90%. Everyone also knows that gzipping can be very cpu intensive. Not anymore.

    I just installed nginx's Gzip Static Module (compile nginx with --with-http_gzip_static_module) on beeets.com. It allows you to pre-cache your gzip files. What?

    Let's say you have the file /css/beeets.css. When a request for beeets.css comes through. the static gzip module will look for /css/beeets.css.gz. If it finds it, it will serve that file as gzipped content. This allows you to gzip your static files using the highest compression ratio (gzip -9) when deploying your site. Nginx then has absolutely no work to do besides serving the static gzip file (it's very good at serving static content).

    Wherever you have a gzip section in your nginx config, you can do:

    gzip_static on;

    That's it. Note that you will have to create the .gz versions of the files yourself, and it's mentioned in the docs that it's better if the original and the .gz files have the same timestamp; so it may be a good idea to "touch" the files after both are created. It's also a good idea to turn the gzip compression down (gzip_comp_level 1..3). This will minimally compress dynamic content without putting too much strain on the server.

    This is a great way to get the best of both worlds: gzipping (faster downloads) without the extra load on the server. Once again, nginx pulls through as the best thing since multi-cellular life. Keep in mind that this only works on static content (css, javascript, etc etc). Dynamic pages can and should be gzipped, but with a lower compression ratio to keep load off the server.

  • 201002.04

    NginX as a caching reverse proxy for PHP

    So I got to thinking. There are some good caching reverse proxies out there, maybe it's time to check one out for beeets. Not that we get a ton of traffic or we really need one, but hey what if we get digged or something? Anyway, the setup now is not really what I call simple. HAproxy sits in front of NginX, which serves static content and sends PHP requests back to PHP-FPM. That's three steps to load a fucking page. Most sites use apache + mod_php (one step)! But I like to tinker, and I like to see requests/second double when I'm running ab on beeets.

    So, I'd like to try something like Varnish (sorry, Squid) but that's adding one more step in between my requests and my content. Sure it would add a great speed boost, but it's another layer of complexity. Plus it's a whole nother service to ramp up on, which is fun but these days my time is limited. I did some research and found what I was looking for.

    NginX has made me cream my pants every time I log onto the server since the day I installed it. It's fast, stable, fast, and amazing. Wow, I love it. Now I read that NginX can cache FastCGI requests based on response caching headers. So I set it up, modified the beeets api to send back some Cache-Control junk, and voilà...a %2800 speed boost on some of the more complicated functions in the API.

    Here's the config I used:

    # in http {}
    fastcgi_cache_path /srv/tmp/cache/fastcgi_cache levels=1:2
                               inactive=5m max_size=500m;
    # after our normal fastcgi_* stuff in server {}
    fastcgi_cache php;
    fastcgi_cache_key $request_uri$request_body;
    fastcgi_cache_valid any 1s;
    fastcgi_pass_header Set-Cookie;
    fastcgi_buffers 64 4k;

    So we're giving it a 500mb cache. It says that any valid cache is saved for 1 second, but this gets overriden with the Cache-Control headers sent by PHP. I'm using $request_body in the cache key because in our API, the actual request is sent through like:

    GET /events/tags/1 HTTP/1.1
    Host: ...

    The params are sent through the HTTP body even in a GET. Why? I spent a good amount of time trying to get the API to accept the params through the query string, but decided that adding $request_body to one line in an NginX config was easier that re-working the structure of the API. So far so good.

    That's FastCGI acting as a reverse proxy cache. Ideally in our setup, HAproxy would be replaced by a reverse proxy cache like Varnish, and NginX would just stupidly forward requests to PHP like it was earlier today...but I like HAproxy. Having a health-checking load-balancer on every web server affords some interesting failover opportunities.

    Anyway, hope this helps someone. NginX can be a caching reverse proxy. Maybe not the best, but sometimes, just sometimes,  simple > faster.