LANcache

Automatically cache game files and updates at LAN parties using Nginx as a reverse proxy.

Forked with thanks from Lochnair/lancache

Requirements

• Ubuntu 16.04
• Nginx compiled with slice and pcre modules
• A DNS server to redirect clients to the cache
• sniproxy to serve HTTPS requests

Installation

1. sudo -i

2. git clone https://github.com/zeropingheroes/lancache.git /etc/nginx

3. cd /etc/nginx

4. cp .env.example .env

5. nano .env

6. ./prepare-configs.sh

7. systemctl restart nginx

Enabling & Disabling Caches

Simply create and remove symlinks from caches-available/ to caches-enabled

• ln -s /etc/nginx/caches-available/cache-name.conf /etc/nginx/caches-enabled/cache-name.conf

• rm /etc/nginx/caches-enabled/cache-name.conf

Clearing Cache

To clear the cache, run:

/etc/nginx/scripts/clear-cache.sh

Removing Specific Items From The Cache

It is desirable to remove items from the cache, in case of corruption, or items being cached that shouldn't have been.

Currently there is no straightforward or reliable way to do this, without paying for Nginx Plus.

The closest we can get is to update the cached item from upstream by using the proxy_cache_bypass config option to tell Nginx to re-fetch the item from upstream when it receives the custom request header "X-Cache-Bypass", forcing it to update the item in cache, and serve the updated item to the client. This can be done using the following CURL snippet:

$ export ITEM_TO_RE_REQUEST="http://valve123.steamcontent.com/depot/282440/chunk/d6556e1b9f7?l=14&e=1446464&sid=103124340&h=2da3a7ad94cab11ff1e6aac28"
$ curl --verbose --header "X-Cache-Bypass: 1" "$ITEM_TO_RE_REQUEST" > /dev/null

$ITEM_TO_RE_REQUEST must be set to the full URL, including the original query string, so that Nginx can pass the request on and get a valid response. If Nginx does not get a valid response, the item will not be updated in the cache.

Problems with this approach

• The item must be re-downloaded from upstream, rather than just being invalidated locally
• The upstream server must respond with a 2xx response code
• If the original request that was cached had a query string with some authentication from the download client, the authentication may have expired, causing the re-request to fail
• Using this method for many items will require getting a big list of URLs, and take a significant amount of time to run
• If the original request was made with a range request, the re-request must use a range request too

Known Issues

Cache Corruption

In the very unlikely event that the cache stores and serves up a corrupted file, only some download clients handle this helpfully for us:

• Blizzard - OK - Re-requests the file with headers Pragma: no-cache and Cache-control: no-cache which causes Nginx to bypass the cache and request a fresh copy of the file from upstream
• Steam - Not OK - Steam will re-request a corrupt file from the cache over and over, but will never send Pragma: no-cache and Cache-control: no-cache headers. This causes the game download to never complete
• Origin - Not OK - All requests are sent with Pragma: no-cache and Cache-control: no-cache and we ignore these or nothing would be cached. If a file is corrupt in the cache there is no mechanism for the Origin client to request Nginx fetches a fresh copy of the file from upstream
• Windows Update - Untested
• Riot - Untested

Contributing

Please submit pull requests to useful changes and enhancements.

Recommended reading: Nginx's Caching blog post