upstream-zulip/puppet/zulip/templates/nginx/s3-cache.template.erb

# nginx does its own DNS resolution, which is necessary here to
# resolve the IP of the S3 server.  Point it at whatever is configured
# first in /etc/resolv.conf.  The validity duration is set to match
# S3's DNS validity.
resolver <%= @nginx_resolver_ip %> valid=300s;
resolver_timeout 10s;

# This cache is only used if S3 file storage is configured.
proxy_cache_path /srv/zulip-uploaded-files-cache
    levels=1:2
    keys_zone=uploads:<%= @s3_memory_cache_size %>
    inactive=<%= @s3_cache_inactive_time %>
    max_size=<%= @s3_disk_cache_size %>;

# This is used when proxying requests to S3; we wish to know if the
# proxied request is asking to override the Content-Disposition in its
# response, so we can adjust our cache key.  Unfortunately, $arg_foo
# style variables pre-parsed from query parameters don't work with
# query parameters with dashes, so we parse it out by hand.  Despite
# needing to be declared at the 'http' level,. nginx applies maps like
# this lazily, so this only affects internal S3 proxied requests.

map $args $s3_disposition_cache_key {
    default "";
    "~(^|&)(?<param>response-content-disposition=[^&]+)" "?$param";
}