select server block based on existence of certain query parameters - nginx

Question

I have a single page application, I want to make it crawlable so I have generated snapshots. My application stack is rails + unicorn + nginx(as reverse proxy).
Now, Aws Opsworks generates a nginx config from this cookbook. I ssh-ed into the system & modified the default config to include the following lines to redirect all requests from search engine bots as follows(they convert the url which contains #! & send a new request with _escaped_fragment_ in query parameters):
if ($args ~ "_escaped_fragment_=(.+)") {
rewrite ^ /snapshots$uri$1?;
}
Everything worked great when I loaded the url in the browser. The issue I am facing is with automating the same thing using chef. Since the code I added was in the config file generated using default cookbook by opsworks, I need a way to define a nginx server block to achieve this. So, I defined the following server block.
server {
listen 80;
server_name example.com;
if ($args ~ "_escaped_fragment_=(.+)") {
set $foo $1;
rewrite ^ /snapshots$uri$foo?;
}
}
But nginx will never select this block given there already exists another server block with the same server_name. So, is there a way that I can define a server block to be selected by nginx based on the existence of _escaped_fragment_ in the $args ?
Something as follows(I know this won't work since regex doesn't match query parameters)
server {
listen 80;
server_name example.com(.+)_escaped_fragment_=(.+);
...
}

Answer 1

In order to do this in chef, you need to create a custom cookbook (if you don't have one already) and a recipe in it which would overwrite the opsworks generated file with your preferred file. In the cookbook you'd need 2 files, nginx template and a recipe to overwrite the default template with the custom one:
mycookbook -> templates -> default -> custom_nginx.erb
mycookbook -> recipes -> customise_nginx.rb
Content of (1):
whatever you want your nginx config file to be, so:
server {
listen 80;
server_name example.com;
if ($args ~ "_escaped_fragment_=(.+)") {
set $foo $1;
rewrite ^ /snapshots$uri$foo?;
}
}
Content of (2):
template "/etc/nginx/sites-enabled/<nginx file name>" do
source "custom_nginx.erb"
user "root"
group "root"
mode "644"
end
service "nginx" do
action :reload
end
Then add mycookbook::customise_nginx to the custom setup recipe section in your layer settings.
If you don't have a custom cookbook already, a bit more set up will be needed:
https://www.digitalocean.com/community/tutorials/how-to-create-simple-chef-cookbooks-to-manage-infrastructure-on-ubuntu
http://docs.aws.amazon.com/opsworks/latest/userguide/workingcookbook-installingcustom-enable.html
Edit:
If you want to keep opsworks config file, you have two options: to take the template that opsworks is using, I'm guessing this one? https://github.com/aws/opsworks-cookbooks/blob/release-chef-11.10/nginx/templat‌​es/default/site.erb, create a copy and put your changes there in file 1 as above. Or use chef to modify the existing file content - for example using FileEdit library (check the second answer to this question)