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I need to write a rewrite rule for Nginx so that if a user tries to go to an old image url:

/images/path/to/image.png

and the file doesnt exist, try to redirect to:

/website_images/path/to/image.png

ONLY if the image exists in the new URL, otherwise continue with the 404. The version of Nginx on our host doesn't have try_files yet.

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3 Answers 3

Reset to default
20 
location /images/ {
    if (-f $request_filename) {
        break;
    }

    rewrite ^/images/(.*) /new_images/$1 permanent;
}

Though, you might want to bug your host to upgrade or find a better host.

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6
  • This will redirect to /new_images on every 404 right? I don't want to do the rewrite unless I know the new_images file exists
    – Jose Fernandez
    Mar 16, 2010 at 13:58
  • This checks to see if the file exists, and if that test fails, it redirects to new_images. What happens after that is not specified here.
    – tylerl
    Jul 31, 2010 at 7:58
  • I'm afraid that your option is considered as common pitfalls by nginx authors nginx.com/resources/wiki/start/topics/tutorials/config_pitfalls/…
    – riverfall
    Jan 22, 2018 at 10:40
  • 2
    @riverfall Heh, I wrote part of that page. My answer was written 8 years ago so yes it's a wee bit outdated, but the original question did specifically state that their host didn't provide a recent version of nginx so they didn't have access to try_files.
    – Martin Fjordvald
    Jan 24, 2018 at 8:29
  • 1
    @Guillaume86 I wouldn't worry about that, an if + rewrite is totally safe and a single STAT check on a file is very light weight. It's much faster than going to a backend application to check for maintenance mode.
    – Martin Fjordvald
    Aug 30, 2019 at 18:37
9

Please don't use if inside a location block. Bad things may happen.

location ~* ^/images/(.+)$ {
    root /www;
    try_files /path/to/$1 /website_images/path_to/$1 /any/dir/$1 @your404;
}

$1 becomes the filename to try in the try_files directive, which is made for what you're trying to accomplish.

This, OR, just rewrite it without checking. If that image isn't there, you'll get a 404 anyway. Honestly if you don't have try_files, the solution should probably be upgrading nginx to the latest stable branch.

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  • 1
    While this answer strictly does not answer the question ("[no] try_files yet"), for future visitors coming here, this answer deserves more up-votes.
    – DerMike
    Apr 18, 2019 at 8:51
6

You could use something like this (untested for your specific case):

location ^/images/(?<imgpath>.*)$ {

    set $no_old  0;
    set $yes_new 0;

    if (!-f $request_filename)
    {
        set $no_old 1;
    }

    if (-f ~* "^/new_path/$imgpath")
    {
        set $yes_new 1$no_old;
    }

    # replacement exists in the new path
    if ($yes_new = 11)
    {
        rewrite ^/images/(.*)$ /new_path/$1 permanent;
    }

    # no image in the new path!
    if ($yes_new = 01)
    {
        return 404;
    }
}

Which is basically an alternative way of writing nested if statements, since you cannot nest in Nginx. See here for official reference on this "hack".

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