The Dark-Knight : How to configure your nginx to retrieve static pages of your website from amazon s3 storage during 502 bad gateway error?

Nginx is widely used as a front-end proxy server to php server which means that when a client makes a request, nginx receives them first and then sends them to php(back-end) server to process them. Nginx has got ability to handle as much as 10000 requests at any point of time.

Now, lets talk about the topic.
There can be situations when you may receive server errors(502 bad gateway, 503 service unavailable, or anything like that). They are seriously nightmares if you have ever faced them. That could create bad impression of you to your users. I have faced it so I can tell you that it is really embarrassing. You probably lose out a lot of your users and other disasters might happen.

The cause for such errors could be from bad coding to high load(good thing, but unable to handle high load is not good).

Now, this is one of the solution where you learn how to configure your system to save yourself from embarrassment. I named it Dark Knight because you shouldn’t need this, but still it guards your website.

Solution:

Suppose, the url to backup has the following form, www.example.com/a/b .

Suppose the static page for www.example.com/a/b is stored in s3 storage as bucket/a/b/a_b.html. The url for same would be https://s3.amazonaws.com/bucket/a/b/a_b.html.

Now following changes can be added in your nginx configuration,

location @static{

rewrite ^ $request_uri;

rewrite /(.*)/(.*) /bucket/$1/$2/$1_$2.html;

proxy_pass https://s3.amazonaws.com;

}

location /index.php {

error_page 502 =200 @static;

fastcgi_intercept_errors on;

#  body

}

 

Explanation:

The usual cause for 502 error is when php fail to handle anymore requests.

The statements, fastcgi_intercept_errors keeps listening if php sends any error to some request, changes the response code for client and error_page redirects to some location on some particular error code(502 here) sent by php.

Now in @static location,

The current value of $uri is /index.php and $request_uri is /a/b. So rewrite it to the form of our static page in s3 bucket url.

The first rewrite changes $uri from /index.php -> /a/b.

The second rewrite changes $uri from /a/b -> /bucket/a/b/a_b.html.

Now proxy_pass directive sends data from given url(static page url) without changing the url.
Note that we can’t append uri after url in proxy_pass in any named_location(it won’t run).
Do provide proper permission to s3 bucket for access.

Cheers. You have learnt now how to configure your nginx to handle 502 error. Similar things can also be done to other server errors.

Here are few related questions, here, here, here, here on stackoverflow.

Latest Comments
  1. kishorer747 September 14, 2015

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